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Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Classification of Animal Kingdom
Professor Paras Nath
College of Agriculture, Fisheries & Forestry
Fiji National University, Koronivia
It is believed that at some point in time two distinct lines evolved from the very
earliest cell forms. They were a group without a nuclear envelope enclosing the nuclear
material, the prokaryotes, and a group with a nuclear envelope enclosing a true nucleus, the
eukaryotes. All animal phyla are multicellular, eukaryotic, heterotrophic organisms. Being
extremely vast and diverse, this kingdom is classified below using flow chart:
Kingdom: Animalia
Subkingdom: Metazoa
Sub-kingdom: Protozoa
Branch: Eumetazoa
Phylum - Protozoa
Branch: Parazoa
Phylum - Porifera
Grade: Radiata
Grade: Bilateria
Phyla
Divisions
Coelenterata
Ctenophora
Deuterostomia
Protostomia
Subdivision
Subdivisions
Enterocelous
Coelomata
Phyla
Lophophorate
Coelomata
Phyla
Chaetognatha
Phoronida
Echinodermata Bryozoa
Pogonophora
(Ectoprocta)
Hemichordata Brachiopoda
Chordata
Schizocoelous
Coelomata
Phyla
Priapulida
Sipunculida
Mollusca
Echiurida
Annelida
Tardigrada
Onychophora
Arthropoda
Pentastomida
Fig. 2. Major groups in animal
Pseudocoelomata
Phyla
Acoelomata
Phyla
Acanthocephala Platyhelminthes
Entoprocta
Mesozoa
Supper– phylum Rhynchocoela
Aschelminthes (Nemeertines)
Phyla
Rotifera
Gastrotricha
Kinorhyncha
Nematoda
Nematomorpha
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
There is variation in the classification of animals proposed by various authors. The
classification proposed by Hymen (1940) with little modification is briefly described
hereunder:
Kingdom: Animalia
This is the largest group of the animal classification which includes entire fauna
(animal population) of the world. It is divided into two sub-kingdoms.
(1) Protozoa and
(2) Metazoa
The contrasting features of the subkingdoms are given hereunder:
1.
Kingdom: Animalia
Subkingdom: Protozoa
Subkingdom: Metazoa
Microscopic, unicellular animals.
Usually large multi-cellular animals.
2.
Structure simple
organelles.
with
sub-cellular Structure complex with strongly marked
cellular differentiation.
3.
Grade of organization protoplasmic.
Grade of organization cellular, cell-tissue,
tissue=organ-system.
4.
Little physiological division of labour.
Physiological
marked.
5.
Life cycle including more than one Life cycle comprising more than one
generation is universal.
generation is rare.
6.
Asexual reproduction universal and Asexual reproduction occurs only in lower
sexual reproduction rare.
metazoan. All reproduce sexually.
7.
Conjugation occurs between adults Conjugation occurs between uni-nucleate
(hologamy).
sperm and ovum (syngamy).
8.
When a cell divides, the daughter cells The fertilized egg repeatedly divides and the
become separate as independent resulting daughter cells remain cohered and
animals.
differentiated to form a distinct body.
9.
The form of individuals may vary even The form of a body is definite for all the
in the same species.
members of a species.
10.
Natural death does not take place due Natural death takes place; hence termed
to lack of a body: hence often termed mortal.
immortal.
division
of
labour
well
Sub-kingdom: I. Protozoa
Protozoa are a diverse group of unicellular eukaryotic organisms, many of which are
motile.About 50,000 species are reported. Originally, protozoa had been defined as
unicellular protists with animal-like behaviour, e.g., movement. Protozoa were regarded as
the partner group of protists to protophyta, which have plant-like behaviour, e.g.
photosynthesis.
Following the Greek root of the name, the singular form is
protozoon/proʊtəˈzoʊ.ɒn/(protos=first, zoon = animal). Its use has, however, partially been
replaced by the word protozoan, which was originally only used as an adjective. In the same
manner the plural form protozoans is sometimes being used instead of protozoa.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
In general, protozoa are referred to as animal-like protists because of movement
(motility). However, both protozoa and protists are paraphyletic groups (not including all
genetic relatives of the group). For example, Entamoeba is more closely related to humans
than to Euglena. "Protozoa" is considered an outdated classification in more formal contexts.
However, the term is still used in children's education.
While there is no exact definition for the term protozoa, it is often referred to as a
unicellular heterotrophicprotist, such as the amoeba and ciliates. The term algae are used for
microorganisms that photosynthesize. However, distinction between protozoa and algae is
often vague. For example, the alga Dinobryon has chloroplasts for photosynthesis, but it can
also feed on organic matter and is motile.
Protozoa is sometimes considered a subkingdom. It was traditionally considered a
phylum under Animalia referring to unicellular animals, with Metazoa referring to
multicellular animals.
Characteristics
Protozoa commonly range from 10 to 52 micrometers, but can grow as large as 1 mm,
and are seen easily by microscope. The largest protozoa known are the deep-sea dwelling
xenophyophores, which can grow up to 20 cm in diameter. They were considered formerly to
be part of the protista family. Protozoa exist throughout aqueous environments and soil,
occupying a range of trophic levels.Protozoa are single-celled animals that feed primarily on
bacteria, but also eat other protozoa, soluble organic matter, and sometimes fungi. They are
several times larger than bacteria – ranging from 1/5000 to 1/50 of an inch (5 to 500 µm) in
diameter. As they eat bacteria, protozoa release excess nitrogen that can then be used by
plants and other members of the food web.
Motility and digestion
Tulodens are 2 of the slow-moving form of protozoa. They move around with whiplike tails called flagella, hair-like structures called cilia, or foot-like structures called
pseudopodia. Others do not move at all. Protozoa may absorb food via their cell membranes,
some, e.g., amoebas, surround food and engulf it, and yet others have openings or "mouth
pores" into which they sweep food, and that engulfing of food is said to be phagocytosis. All
protozoa digest their food in stomach-like compartments called vacuoles.
Pellicle
The pellicle is a thin layer supporting the cell membrane in various protozoa,
protecting them and allowing them to retain their shape, especially during locomotion,
allowing the organism to be more hydrodynamic. They vary from flexible and elastic to rigid.
Although somewhat stiff, the pellicle is also flexible and allows the protist to fit into tighter
spaces. In ciliates and Apicomplexa, it is formed from closely packed vesicles called alveoli.
In euglenids, it is formed from protein strips arranged spirally along the length of the body.
Examples of protists with a pellicle are the euglenoids and the paramecium, a ciliate. The
pellicle consists of many bacteria that adhere to the surface by their attachment pili. Thus,
attachment pili allow the organisms to remain in the broth, from which they take nutrients,
while they congregate near air, where the oxygen concentration is greatest.
Ecological role
As components of the micro- and meiofauna, protozoa are an important food source
for microinvertebrates. Thus, the ecological role of protozoa in the transfer of bacterial and
algal production to successive trophic levels is important. As predators, they prey upon
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
unicellular or filamentous algae, bacteria, and microfungi. Protozoa are both herbivores and
consumers in the decomposer link of the food chain. They also control bacteria populations
and biomass to some extent. Protozoa such as the malaria parasites (Plasmodium spp.),
trypanosomes and leishmania, are also important disease causing agents in humans.
Life cycle
Some protozoa have life stages alternating between proliferative stages (e.g.,
trophozoites) and dormant cysts. As cysts, protozoa can survive harsh conditions, such as
exposure to extreme temperatures or harmful chemicals, or long periods without access to
nutrients, water, or oxygen for a period of time. Being a cyst enables parasitic species to
survive outside of a host, and allows their transmission from one host to another. When
protozoa are in the form of trophozoites (Greek, tropho = to nourish), they actively feed. The
conversion of a trophozoite to cyst form is known as encystation, while the process of
transforming back into a trophozoite is known as excystation. Protozoa can reproduce by
binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, while
some use a combination, (e.g., Coccidia). An individual protozoan is hermaphroditic.
What do protozoa do?
Protozoa play an important role in mineralizing nutrients, making them available for
use by plants and other soil organisms. Protozoa (and nematodes) have a lower concentration
of nitrogen in their cells than the bacteria they eat. (The ratio of carbon to nitrogen for
protozoa is 10:1 or much more and 3:1 to 10:1 for bacteria.) Bacteria eaten by protozoa
contain too much nitrogen for the amount of carbon protozoa need. They release the excess
nitrogen in the form of ammonium (NH4+). This usually occurs near the root system of a
plant. Bacteria and other organisms rapidly take up most of the ammonium, but some is used
by the plant. The explanation of mineralization and immobilization is given in Fig.1a.below:
Fig.2a. Path ways showing mineralization and immobilization of nutrients in soil.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Another role that protozoa play is in regulating bacteria populations. When they graze
on bacteria, protozoa stimulate growth of the bacterial population (and, in turn,
decomposition rates and soil aggregation.) Exactly why this happens is under some debate,
but grazing can be thought of like pruning a tree – a small amount enhances growth, too
much reduces growth or will modify the mix of species in the bacterial community.
Protozoa are also an important food source for other soil organisms and help to
suppress disease by competing with or feeding on pathogens.
Where are protozoa?
Protozoa need bacteria to eat and water in which to move, so moisture plays a big role
in determining which types of protozoa will be present and active. Like bacteria, protozoa are
particularly active in the rhizosphere next to roots.
Typical numbers of protozoa in soil vary widely – from a thousand per teaspoon in
low fertility soils to a million per teaspoon in some highly fertile soils. Fungal-dominated
soils (e.g. forests) tend to have more testate amoebae and ciliates than other types. In
bacterial-dominated soils, flagellates and naked amoebae predominate. In general, high claycontent soils contain a higher number of smaller protozoa (flagellates and naked amoebae),
while coarser textured soils contain more large flagellates, amoebae of both varieties, and
ciliates.Protozoa play an important role in nutrient cycling by feeding intensively on bacteria
(Fig.7b.,1c.,1d. and1e.). Flagellates have one or two flagella which they use to propel or pull
their way through soil. Ciliates are the largest of the protozoa and the least numerous. They
consume up to ten thousand bacteria per day, and release plant available nitrogen. Ciliates use
the fine cilia along their bodies like oars to move rapidly through soil.
Fig.3b.The speck-like bacteria next to the oval
protozoa and large, angular sand particle.
Fig.4c.Bacteria ingested by an amoeba.
Fig.6d.A flagellum extending from the
protozoan on the left and the tiny specks are
bacteria.
Fig.5e.Ciliates showing the fine cilia along their
bodies like oars to move rapidly through soil.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Nematodes and Protozoa
Protozoa and bacterial-feeding nematodes compete for their common food resource: bacteria.
Some soils have high numbers of either nematodes or protozoa, but not both. The
significance of this difference to plants is not known. Both groups consume bacteria and
release NH4+.
Soil Dwelling Vampires
Most protozoa eat bacteria, but one group of amoebae, the vampyrellids, eat fungi.
The perfectly round holes drilled through the fungal cell wall, much like the purported
puncture marks on the neck of a vampire’s victim, are evidence of the presence of
vampyrellid amoebae. The amoebae attach to the surface of fungal hyphae and generate
enzymes that eat through the fungal cell wall. The amoeba then sucks dry or engulfs the
cytoplasm inside the fungal cell before moving on to its next victim.
Vampyrellids attack many fungi including root pathogens, such as Gaeumannomyces
graminis, shown in the following Fig.1f. This fungus attacks wheat roots and causes take-all
disease.
Fig.1f.Vampyrellids attacking fungal root pathogen (Gaeumannomyces graminis).
Classification
All protozoal species are assigned to the kingdom Protista in the Whittaker
classification. The protozoa are then placed into various groups primarily on the basis of how
they move. The groups are called phyla (singular, phylum) by some microbiologists and
classes by others. Members of the four major groups are illustrated in Fig. 1.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Fig.1.An array of protozoa showing representatives of the four major groups.
Protozoa were previously often grouped in the kingdom of Protista, together with the
plant-like algae and fungus-like slime molds. As a result of 21st-century systematics,
protozoa, along with ciliates, mastigophorans, and apicomplexans, are arranged as animallike protists. Protozoa are unicellular organisms and are often called the animal-like protists
because they subsist entirely on other organisms for food. Most protozoa can move about on
their own. Amoebas, trypanosomesandparameciaare all examples of animal-like protists
(Figs. 2 to 5).
Protozoa are classified into three groups based on their shape: Ciliates are the largest
and move by means of hair-like cilia. They eat the other two types of protozoa, as well as
bacteria. Amoebae also can be quite large and move by means of a temporary foot or
“pseudopod.” Amoebae are further divided into testate amoebae (which make a shell-like
covering) and naked amoebae (without a covering). Flagellates are the smallest of the
protozoa and use a few whip-like flagella to move.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Fig. 4. Paramecium aurelia, the best
known of all ciliates
Fig.5. Structure of a Paramecium aurelia showing various
body features.
The kingdom Protista or Protoctista now includes about 80,000 species of singlecelled organisms that have the genetic material enclosed in a nucleus and have membrane
bound organelles, namely, golgi body, mitochondria, lysosomes, centrosome etc. The
kingdom includes both plant Protista (=Protophyta) and animal Protista (=Protozoa).
In
modern classifications Protozoa is considered as a convenient name for unicellular animals
and is not given any rank or status.
Modified Sleigh’s Systemof Classification(by A. Pechenik, 2002)
Kingdom: Protozoa (14 phyla)
1. Phylum: Ciliophora(ciliates).
2. Phylum:Amoebozoa(Amoebas).
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
3. Phylum:Radiozoa(radiolarians).
4. Phylum:Heliozoa (sun animalcules).
Flagellated Protozoa
5.
6.
7.
8.
9.
Phylum:Trichozoa (Trichomonas).
Phylum:Euglenozoa (Euglena).
Phylum:Dinozoa (Dinoflagellates).
Phylum:Choanozoa (Choanoflagellates).
Phylum:Metamonada (Giardia).
Spore-Forming Protozoa
10. Phylum:Apicomplexa (=Sporoza), includes three subphyla.
Honorary Protozoa
11.
12.
13.
14.
Phylum:Labyrinthomorpha (Slime-nets).
Phylum:Opalozoa (Opalina).
Phylum:Microsporidea (now transferred to fungi).
Phylum:Myxozoa (now shifted to kingdom Animalia)
Kingdom:Chromista, Slime-nets (Labyrinthomorpha) and Opalina (Opalinata) have been
brought under this new kingdom.
Subkingdom: II. Metazoa
The subkingdom Metazoa comprises multicellular animals as per the old
classification. According to Whittaker Animals are multicellular, eukaryoticorganisms of the
kingdomAnimalia or Metazoa. Their body plan eventually becomes fixed as they develop,
although some undergo a process of metamorphosis later on in their lives. Most animals are
motile, meaning they can move spontaneously and independently. All animals must ingest
other organisms or their products for sustenance (Heterotrophic).
Most known animal phyla appeared in the fossil record as marine species during the
Cambrian explosion, about 542 million years ago. Animals are divided into various subgroups, including birds, mammals, amphibians, reptiles, fish and insects.It is divided into two
branches.
1. Branch: Parazoa
2. Branch: Eumetazoa
The contrasting features of the two branches are given in the following tables:
Subkingdom: Metazoa
Branch: Parazoa
Branch: Eumetazoa
1. Animals sessile.
Animals mostly mobile.
2. Tissues absent or poorly defined.
Tissues well defined.
3. No organs.
Organs well marked.
4
No mouth and digestive tract.
Mostly with mouth and digestive tract.
5. Body surface porous.
Body surface not porous.
6. One to many internal cavities lined by
Body cavities not lined by
choanocytes.
choanocytes.
7. Physiological division of labour not well
Physiological division of labour well
marked.
marked.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Branch: I. Parazoa
The Parazoa are an ancestral subkingdom of animals, literally translated as "beside
the animals". Parazoans differ from their choanoflagellate ancestors in that they are not
microscopic and have differentiated cells. However, they are an outgroup of the animal
phylogenetic tree being that they are multicellular and do not have tissues or organs. The only
surviving parazoans are the sponges (Fig.6 and 7), which belong to the phylum Porifera, and
the Trichoplax in the phylum Placozoa.
Fig.6. Underwater photograph of a marine sponge.
Fig.7. Different species of sponges.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Phylum: Porifera
The animals of the phylumPorifera (/pɒˈrɪfərə/; meaning "pore bearer" are sponges
(Fig.8). They are multicellular organisms that have bodies full of pores and channels allowing
water to circulate through them, consisting of jelly-like mesohyl (formerly known as
mesenchyme)sandwiched between two thin layers of cells. Sponges have unspecialized cells
that can transform into other types and which often migrate between the main cell layers and
the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems.
Instead, most rely on maintaining a constant water flow through their bodies to obtain food
and oxygen and to remove wastes. They are mostly irregular with a system of water canals
and pores. Internal surface lined with choanocytes. They are sessile, marine, a few in freshwater and are solitary or colonial. They display no body symmetry (are asymmetrical); all
other animal groups display some sort of symmetry. There are currently 5000 species of
sponges, 150 of which are freshwater. Larvae are planktonic and adults are sessile.
Fig. 9.Leucosolenia: A. An individual, and B. Its L. S.
Fig.8. Stove-pipe sponge (Aplysina
archeri) showing pink variation.
Branch: II Eumetazoa
Eumetazoa (Greek: εὖ [eu], well + μετά [metá], after + ζῷον [zóon], animal) is a
clade comprising all major animal groups except sponges, placozoa, and several other
obscure or extinct life forms, such as Dickinsonia. This includes radially, biradially or
bilaterally symmetrical animals. The clade is usually held to contain at least Ctenophora,
Cnidaria, and Bilateria. Whether mesozoans and placozoans belong is in dispute.
Characteristics of eumetazoans include true tissues organized into germ layers, and an
embryo that goes through a gastrula stage. A Lancelet (or Amphioxus) specimen of
Branchiostoma lanceolatum (Pallas, 1774) collected in coarse sand sediments (600
µm) on
the Belgian continental shelf is shown in Fig.10.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Fig.10.A Lancelet (or Amphioxus) specimen of Branchiostoma lanceolatum (Pallas, 1774)
The eumetazoans are a major group of animals in the Five Kingdoms classification
comprising all animals except the sponges, placozoans and mesozoans and are divided in the
following two grades:
1. Radiata
2. Bilateria
Their contrasting features are given in the following table:
Branch: Eumetazoa
Grade: Radiata
Grade: Bilateria
1. Body
radially
or
biradially Body bilaterally symmetrical. Some time radials.
symmetrical. Some time bilateral.
2. Bilateral symmetry is a secondary Radial symmetry is a secondary adaptation.
adaptation.
3. Organ-systems are incipient, i.e. not Organ-systems well marked.
well marked.
4. Mesoderm is not developed.
Mesoderm is well developed.
5. Coelomic cavity invariably absent.
Either no coelomic cavtty or pseudocoelom or well
developed true coelom.
6. Tentacles with nematocysts, comb Tentacles, if present, without nematocysts. No comb
rows in some.
rows.
7. Principal external opening of Principal external openings of digestive cavity are
digestive cavity is mouth.
mouth and anus.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Grade: I. Radiata
In the early 19th century, Georges Cuvier united ctenophores and cnidarians in the
Radiata. Thomas Cavalier-Smith, in 1983, redefined Radiata as a subkingdom consisting of
Porifera, Myxozoa, Placozoa, Cnidaria and Ctenophora. Lynn Margulis and K. V. Schwartz
later redefined Radiata in their Five Kingdom classification, this time including only Cnidaria
and Ctenophora.The animals of this group are diploblastic with radial symmetry (radiate) and
bear tentacles (tentaculate). Their digestive cavity opens externally through mouth.
Phylum: Coelenterata (With hollow
intestine) or Cnidaria (Nrettle- bearing).
About 10,000 species. Mouth encircled by
tentacles bearing nematocysts. Body cavity as
coelenteron. Sessile or free swimming.
Solitry or colonial. Marine or freshwater.
Example: Aurelia, Hydra, Obelia, Corals, etc.
Phylum-Ctenophora (Comb-jellies). About
90 species. Symmetry biradial. Two tentacles
and eight longitudinal rows of ciliated
combs, free swimming and marine.
Examples:
Coeloplana,
Pleurobrachia,
Ctenoplana, etc.
Fig.11. Aurelia sp.
Fig.12. Coeloplana sp.
Grade: II. Bilateria
The bilateria/ˌbaɪləˈtɪəriə/are all animals having a bilateral symmetry, i.e. they have a
front and a back end, as well as an upside and downside. In contrast, radially symmetrical
animals like jellyfish have a topside and downside, but no front and back. The bilateria are a
major group of animals, including the majority of phyla but not sponges, cnidarians,
placozoans and ctenophores. For the most part, Bilateria embryos display three different germ
layers, called the endoderm, mesoderm, and ectoderm. From this they are called triploblastic.
Nearly all are bilaterally symmetrical, or approximately so; the most notable exception is the
echinoderms, which achieve near-radial symmetry as adults, but are bilaterally symmetrical
as larvae. Except for a few phyla (i.e. flatworms and gnathostomulids), the Bilateria have
complete digestive tracts with separate mouth and anus. Some Bilateria lack body cavities
(acoelomates, i.e. Platyhelminthes, Gastrotricha and Gnathostomulida), while others display
primary body cavities (deriving from the blastocoel, as pseudocoel) and/or secondary cavities
(that appear de novo, for example the coelom). This grade is subdivided into two divisions:
1. Protostomia
2. Deuterostomia
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Their contrasting characters are listed in the following table.
Grade: Bilateria
1.
Divison: Protostomia
Mouth arises from blastopore or from the
anterior margin of blastopore.
Division: Deuterostomia
Mouth arises anteriorly some distance away
from blastopore.
2.
Coelom absent or Pseudocoelom (a Coelom developed as enterocoel.
persistent
blastocoel)
or
coelom
developed as schizocoel.
3.
Cleavage spiral and determinate.
Cleavage radial and indeterminate.
Division I: Protostomia
Protostomia (from Greek meaning "mouth first") is a clade of animals. Most animals
have bilateral symmetry and three germ layers. The major distinctions between
deuterostomes and protostomes are found in embryonic development.The division comprises
animals in which the mouth arises from or near blastopore.The protostomes were so named
because it used to be thought that in their embryos the dent formed the mouth while the anus
was formed later, at the opening made by the other end of the gut.
Fig.13.ACaribbean Reef Squid, an example of a protostome.
It is subdivided into following four subdivisions:
1.
2.
3.
4.
Acoelomata,
Paeuudocoelomata,
Schizocoelous coelomata
Lophophorate coelomata
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Subdivision (i): Acoelomata
No body or coelom. Space between body wall and digestive cavity is occupied by
mesenchyme.An acœlomate animal is characterized by the absence of coelom and thus the
internal organs derived from mesoderm.This is called a blastocoelienne cavity. In these
animals, the digestive system is very simple and has only one hole, food intake is mainly
through the skin.They also have a bilateral symmetry of the body.
These animals are part of triploblastic that is to say that their embryo has three germ
layers.The third sheet, the mesoderm, in this case has allowed the appearance of the muscles,
which results in an autonomous locomotion and concentration of sensory organs at the front
of the body (in other words, cephalization).
These groups of animals have many species parasites and are the cause of many
diseases, often fatal diseases such as tapeworm, the liver fluke, the schistosomiasis, the
schistosomiasis or onchocerciasis (river blindness).
Phylum: Platyhleminthes
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes
(from the Greek πλατύ, platy, meaning "flat" andἕλμινς (root: ἑλμινθ -), helminth-, meaning
worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied
invertebrateanimals. Unlike other bilaterians, they have no body cavity, and no specialized
circulatory and respiratoryorgans, which restrict them to having flattened shapes that allow
oxygen and nutrients to pass through their bodies by diffusion (Fig. 14). The digestive cavity
has only one opening for both the ingestion (intake of nutrients) and egestion (removal of
undigested wastes); as a result, the food cannot be processed continuously.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Fig.14. a. A free-living planarian (Dugesia).
Fig.14. b.A fluke worm (Probolitrema).
Platyhelminthes consists of the unsegmented dorsoventrally flattenedflatworms,
which includes both free-living and parasitic species. They have bilateral symmetry, and can
move by using layers of muscles, or in some species, by gliding along a slime trail using cilia.
Flatworms are slightly less developed than segmented worms due to their lack of a
circulatory system and complete digestive system. Instead, flatworms absorb nutrients
through their skin and excrete wastes using specialized "flame cells." Some flatworms have
primitive light-sensing "eyes" that allow them to move either towards or away from light,
while other species have different types of sensors on their bodies, including chemical,
balance, and water movement receptors. Most species of flatworms reproduce either sexually
or asexually.Examples: Fasciola, Planaria, Taenia, etc.
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L 4 ENT 402: Agricultural Biology
Phylum: Mesozoa (Middle animals).
The Mesozoa are enigmatic, minuscule, worm-like parasites of marine invertebrates.
As of 2012 it was still unclear whether they are degenerate platyhelminthes (flatworms) or
truly-primitive, basalmetazoans. Generally, these tiny, elusive creatures consist of a
somatoderm (outer layer) of ciliated cells surrounding one or more reproductive cells.
Decades ago, Mesozoa were classified as a phylum. Molecularphylogeny studies, however,
have shown that the mysterious mesozoans are polyphyletic. That is, they consist of at least
two unrelated groups.The Mesozoa are a small phylum of small and poorly understood
animals. They have very simple bodies, often consisting of less than 50 cells. All known
species are internal parasites of marine invertebrates.About 50 species described. No organs.
Body with an outer single layer of cells enclosing reproductive cells. Examples: Rhopalura,
Dicyema, etc.
Fig. 15. a.Rhopalura.
Phylum: Rhynchocoela or Nemertinea (Ribbon worms).
About 750 species. Body dorsoventrally flattened with both mouth and anus. Mostly
marine, few terrestrial and freshwater, Examples: Cerebratulus, Lineus, etc.
Subdivision (ii): Pseudocoelomata
Pseudocoelomate (s ´´dōsē´l māt´´) are a group of invertebrates with a three-layered
body that has a fluid-filled body cavity (pseudocoelom) between the endoderm and the
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mesoderm (the innermost and middle tissue layers). Body cavity is a pseudocoelom which is
a persistent blastocoel, not lined by mesoderm. The pseudocoelom is contrasted with the
coelom of mollusks, annelid worms, and the more complex animals (including humans and
other vertebrates). Pseudocoelomates lack a circulatory system, and the pseudocoelom itself
lacks the endothelial lining of a coelom. The hydrostatic pressure of the pseudocoelom gives
the body a supportive framework that acts as a skeleton. Nematodes or roundworms, rotifers,
acanthocephalans (spiny-headed worms), kinorhynchs and nematomorphs or horsehair
worms are pseudocoelomates.
Phylum: Acanthocephala
Acanthocephala (Greek ἄκανθος, akanthos, thorn + κεφαλή, kephale, head) is a
phylum of minute parasitic worms known as acanthocephalans, thorny-headed worms, or
spiny-headed worms, characterized by the presence of a protrusible proboscis with recurved
spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans are highly
adapted to a parasitic mode of life, and have lost many organs and structures through
evolutionary processes. Acanthocephalans lack a mouth or digestive cavity. This is a feature
they share with the cestoda (tapeworms), although the two groups are not closely related.
Adult stages live in the intestines of their host and uptake nutrients which have been digested
by the host, directly, through their body surface. Acanthocephalans have complex life cycles,
involving at least two hosts, which may include invertebrates, fishes, amphibians, birds, and
mammals.
About
1150
species
have
been
described.Example:
Pomphorhynchus,Acanthocephalus, etc.
Fig.16. Adult Pomphorhynchus in abluefish
(Pomatomus saltatrix).
Fig.17. Morphological features of Corynosoma
wegeneri (Phylum Acanthocephala).
The endoparasitic thorny-headed worms (1150 species) require two hosts to complete
the life cycle. The juveniles are parasitic in crustaceans and insects. Adults live in the
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digestive tract of vertebrates, especially fish. The body of the adult is elongate and composed
of a trunk, a short head region and a proboscis covered with recurved spines with which the
worms embed themselves in the host’s gut wall. The proboscis is not used for feeding, only
for attachment, since like tapeworms; acanthocephalans have no gut and absorb nutrients
directly from the host’s gut through the tegument.
Eggs are passed into the environment; they develop further when ingested by the
intermediate host. The juvenile acanthor bears an anterior crown of hooks used to penetrate
the tissues of the intermediate host, where it undergoes developmental changes to form an
infective cystacanth. When the intermediate host is eaten by the definite host, the cystacanth
excysts and attaches to the gut wall and develops into an adult.
Fig.18. Rhadinorhynchussp.
Fig.19. Polymorphus spp.
Fig. 21. The largest acanthocephalan,
Macracanthorhyncus hirudinaceous.
Fig.20.Profillicolus bolulus in the Fig.22. Lateral and face view of proboscis of
intestine of the eider duck.
Hypoechinorhynchus thermaceri Buron.
Rhadinorhynchus sp.(Fig.18) and Polymorphus spp. (Fig.19) are showing the spiny
proboscis that gives acanthocephalans their name. Profillicolus bolulus(Fig.20) in the
intestine of the eider duck shows the ‘orchard effect’: spacing of the parasites so that ‘they do
not tread on each other’s toes’. The lateral and face view of the proboscis of
Hypoechinorhynchus thermaceriare shown through the electron micrographs in the
Fig.22.Acanthocephalans often exist in great numbers in the vertebrate host and can cause
much damage to the gut wall.The largest acanthocephalan, Macracanthorhyncus
hirudinaceous, causes serious disease in its definitive host, the pig(Fig.21). Beetles act as
hosts for the juveniles.
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Phylum: Entoprocta (Moss animals).
"Entoprocta", coined in 1870, means "anus inside". The alternative name
"Kamptozoa", meaning "bent" or "curved" animals, was assigned in 1929. Some authors use
"Entoprocta", while others prefer "Kamptozoa".
Most species are colonial, and their members are known as "zooids", since they are
not fully independent animals. Zooids are typically 1 millimetre (0.039 in) long but ranging
from 0.1 to 7 millimetres (0.0039 to 0.28 in) long.
Entoproctaisa phylum of mostly aquatic animals.While the great majority is marine,
two species live in freshwater, Loxosomatoides sirindhornae reported in 2004 in central
Thailand and Urnatella gracilis found in all the continents except Antarctica. Colonial
species are found in all the oceans, living on rocks, shells, algae and underwater buildings.
These are solitary or colonial and suspension feeders by means of tentacles, however some
species occur commensally on animals that have their own feeding current system (e.g.
poriferans).The solitary species, which are marine, live on other animals that feed by
producing water currents, such as sponges, ectoprocts and sessile annelids.The digestive tube
is U-shaped. Mouth and anus are close together and surrounded by a tentacular crown (Fig.23
and 24).The zooids absorb oxygen and emit carbon dioxide by diffusion, which works well
for small animals.
Mature individuals are goblet-shaped, on relatively long stalks.Some species eject
unfertilized ova into the water, while others keep their ova in brood chambers until they
hatch, and some of these species use placenta-like organs to nourish the developing eggs.
After hatching, the larvae swim for a short time and then settle on a surface. There they
metamorphose, and the larval gut generally rotates by up to 180°, so that the mouth and anus
face upwards. Both colonial and solitary species also reproduce by cloning – solitary species
grow clones in the space between the tentacles and then release them when developed, while
colonial ones produce new members from the stalks or from corridor-like stolons.
Most families of entoprocts are colonial, and all but 2 of the 150 reported species are
marine. A few solitary species can move slowly.Example: Pedicellina, Loxosomaa, etc.
Fig.23. Pedicellina cernua (Pallas, 1774) from Guernsey, a British Crown dependent island
in the English Channel. Entire colony × 27. The colony has three growing ends – a; 1–8 –
individuals of colony; 1 and 8 are quite immature; 7 is still young, tentacles retracted; 2 is
seen in longitudinal section; g – generative organ, and below it the ganglion; m – mouth; r –
rectum; s – stomach; between g and r are three embryos in the brood-pouch; the tentacles are
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retracted; in 5 and 6 the tentacles are expanded; in 6 two embryos are seen within the circle of
the tentacles, to the left of them is the rectum, and to the right the mouth; 3 is in the act of
losing its calyx, and has already developed the beginning of a new polypide-bud; in 4 the
primary calyx has been lost, and the new calyx is clearly marked off from the stalk.
Fig.24. Body plan of Entoprocta.
Super-phylum: Aschelminthes
The members of this Super-phylum are commonly known as sac worms. This group is
an assemblage of pseudocoelomates with an anterior mouth, posterior anus and straight
digestive tube. The Aschelminthes (also known as Aeschelminthes), closely associated with
the Platyhelminthes, are an obsolete phylum of pseudocoelomate and other similar animals
that are no longer considered closely related and have been promoted to phyla in their own
right. The term Aschelminth is now generally only used as an informal name for any
member of the approximately ten different invertebrate phyla formerly included within
Aschelminthes.
It is considered a polyphyletic group.Although invertebrate experts do not necessarily
agree on these categorizations, groups that are generally incorporated into Aschelminthes are
briefly described hereunder:
Phylum: Rotifera
The word "rotifer" is derived from a Latin word meaning "wheel-bearer", due to the
corona around the mouth that in concerted sequential motion resembles a wheel (though the
organ does not actually rotate).The rotifers (Rotifera, commonly called wheelanimals or
wheel animalcules) make up a phylum of microscopic and near-microscopic
pseudocoelomateanimals. They were first described by Rev. John Harris in 1696, and other
forms were described by Anton van Leeuwenhoek in 1703. Most rotifers are around 0.1–
0.5 mm long (although their size can range from 50 μm to over 2 millimeters), and are
common in freshwater environments throughout the world with a few saltwater species; for
example, those of genus Synchaeta. Some rotifers are free swimming and truly planktonic,
others move by inchworming along a substrate, and some are sessile, living inside tubes or
gelatinous holdfasts that are attached to a substrate. About 2200 species of rotifers have been
described. Anterior end with a ciliated crown.Pharynx with internal jaws. Examples:
Philodina, Rotatoria, etc. About 25 species are colonial (e.g., Sinantherina semibullata),
either sessile or planktonic. Rotifers are an important part of the freshwater zooplankton,
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being a major foodsource and with many species also contributing to the decomposition of
soil organic matter. Most species of the rotifers are cosmopolitan, but there are also some
endemic species, like Cephalodella vittata to Lake Baikal. Recent barcoding evidence,
however, suggests that some 'cosmopolitan' species, such as Brachionus plicatilis, B.
calyciflorus, Lecane bulla, among others, are actually species complexes.
Fig.25. Colony of Rotifers (Sinantheria socialis, Family: Flosculariidae)
on Egeria densa (North German Lake).
Fig.26. Scanning electron micrographs showing morphological
variation of bdelloid rotifers and their jaws.
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Phylum: Gastrotricha
The gastrotrichs (from Greek γαστήρ, gaster ["belly"], and θρίξ, thrix ["hair"]), often
called hairy backs or hairy stomach worms, are a phylum of microscopic (0.06-3.0 mm),
pseudocoelomateanimals abundant in fresh water and marine environments. Most fresh water
species are part of the periphyton and benthos. Marine species are found mostly interstitially
in between sediment particles, while terrestrial species live in the water films around grains
of soil. The common name "hairy back" apparently arises from a mistranslation of
"gastrotrich;" the better common name for all gastrotrichs is "hairy belly," which refers to
ventral cilia present in most species. "Hairy back" should be limited to the large Genus
Chaetonotus, whose members usually have backs covered with hair-like spines.
Gastrotrichs are bilaterally symmetric, with a transparent body and a flat underside.
Many species have a pair of short projections at the posterior end (Fig.27, Fig.28 and Fig.29).
The body is covered with cilia, especially about the mouth and on the ventral surface, and has
two terminal projections with cement glands that serve in adhesion. This is a double-gland
system where one gland secretes the glue and another secretes a de-adhesive to sever the
connection. Like many microscopic animals, their locomotion is primarily powered by
hydrostatics. About 150 species described. Ventral surface is flattened andciliated. Cuticle is
with spines, plates or scales. These are found in freshwater and marine water bodies.
Examples: Chaetonotus, Macrodasys, etc.
Fig.27.
Fig.29.
Fig.28.
Fig.27. & 28.Photographs of two species of gastrotrich.Fig.29. A generalized Gastrotrich body parts.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
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Phylum: Kinorhyncha
Kinorhyncha (ki-no-RINK-a) is formed from two Greek roots that mean "moving by
the snout". Kinorhyncha (Gr. κίνηω, kīneō 'move' + ρυνχος, rhynchos 'snout') is a phylum of
small (1 mm or less) marine pseudocoelomateinvertebrates that are widespread in mud or
sand at all depths as part of the meiobenthos. The reference is to the way the animal moves
by everting its mouth cone.They are called spiny-crown worm, jaw-moving worms,mud
dragons.Kinorhynchans are segmented, limbless animals, with a body consisting of a head,
neck, and a trunk of eleven segments. Cuticle segmented and with recurved spines. Unlike
some similar invertebrates, they do not have external cilia, but instead have a number of
spines along the body, plus up to seven circles of spines around the head. These recurved
spines are used for locomotion, withdrawing the head and pushing forward, then gripping the
substrate with the spines while drawing up the body.Anterior end is spiny. About 180 species
are known. Exampels: Echinoders, Pycnophyses, etc.
Fig.30. Body plan ofKinorhyncha and some other images of spiny-crown worm.
Phylum: Nematoda
The nematodes/ˈnɛmətoʊdz/or roundworms comprise the phylumNematoda.This is
a phylum of worms, having a long, round, and generally smooth body; the roundworms. They
are mostly parasites, in plants and animals, but some are free-living in soil or water. This
phylum is also called Nematoidea. They are a diverse animal phylum inhabiting a very broad
range of environments. Nematode species can be difficult to distinguish; and although over
28,000 have been described, of which over 16,000 are parasitic, the total number of nematode
species has been estimated to be about 1 million. Unlike cnidarians and flatworms,
nematodes have tubular digestive systems with openings at both ends.
Nematodes are slenderand cylindrical worms havingradial or biradial arrangement of
structures around the mouth. They are typically less than 2.5 mm (0.098 in) long. The
smallest nematodes are microscopic, while free-living species can reach as much as 5 cm
(2.0 in), and some parasitic species are larger still, reaching over a meter in length. The body
is often ornamented with ridges, rings, bristles, or other distinctive structures.
The head of a nematode is relatively distinct. Whereas the rest of the body is
bilaterally symmetrical, the head is radially symmetrical, with sensory bristles and, in many
cases, solid 'head-shields' radiating outwards around the mouth. The mouth has either three or
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six lips, which often bear a series of teeth on their inner edges. An adhesive 'caudal gland' is
often found at the tip of the tail. The body features of nematode are shown in Fig.31.
Nematodes have successfully adapted to nearly every ecosystem from marine to fresh
water, to soils, and from the Polar Regions to the tropics, as well as the highest to the lowest
of elevations. They are ubiquitous in freshwater, marine, and terrestrial environments, where
they often outnumber other animals in both individual and species counts, and are found in
locations as diverse as mountains, deserts and oceanic trenches. They are free-living or
parasitic in nature. They are found in every part of the earth's lithosphere. They represent, for
example, 90% of all life forms on the ocean floor.Their numerical dominance, often
exceeding a million individuals per square meter and accounting for about 80% of all
individual animals on earth, their diversity of life cycles, and their presence at various trophic
levels point at an important role in many ecosystems. Their many parasitic forms include
pathogens in most plants and animals (including humans). Some nematodes can undergo
cryptobiosis.
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One group of carnivorous fungi, the nematophagous fungi, is predators of soil
nematodes. They set enticements for the nematodes in the form of lassos or adhesive
structures.Nematodes have even been found at great depth (0.9–3.6 km) below the surface of
the Earth in gold mines in South Africa.
The different species of free-living nematodes usually consists of four moults of the
cuticle during growth and feed on materials as varied as algae, fungi, small animals, faecal
matter, dead organisms and living tissues. Free-living marine nematodes are important and
abundant members of the meiobenthos. They play an important role in the decomposition
process, aid in recycling of nutrients in marine environments, and are sensitive to changes in
the environment caused by pollution. One roundworm of note, Caenorhabditis elegans, lives
in the soil and has found much use as a model organism. C. elegans has had its entire genome
sequenced, as well as the developmental fate of every cell determined, and every neuron
mapped.
Nematodes commonly parasitic on humans include ascarids (Ascaris), filarias,
hookworms, pinworms (Enterobius) and whipworms (Trichuris trichiura). The species
Trichinella spiralis, commonly known as the 'trichina worm', occurs in rats, pigs, and
humans, and is responsible for the disease trichinosis. Baylisascaris usually infests wild
animals, but can be deadly to humans, as well. Dirofilaria immitisheartworms are known for
causing heartworm disease by inhabiting the hearts, arteries, and lungs of dogs and some cats.
Haemonchus contortus is one of the most abundant infectious agents in sheep around the
world, causing great economic damage to sheep. In contrast, entomopathogenic nematodes
parasitize insects and are considered by humans to be beneficial.Some common parasitic
nematodes are Ascaris, Trichinella, Wuchereria, Ancylostoma, Enterobius,etc.
Depending on the species, a nematode may be beneficial or detrimental to plant
health. From agricultural and horticulture perspectives, the two categories of nematodes are
the predatory ones, which will kill garden pests like cutworms, and the pest nematodes (Fig.),
like the root-knot nematode, which attack plants, and those that act as vectors spreading plant
viruses between crop plants. Predatory nematodes can be bred by soaking a specific recipe of
leaves and other detritus in water, in a dark, cool place, and can even be purchased as an
organic form of pest control
Fig.31. Low-temperature scanning electron micrograph
ofsoybean cyst nematode and its egg. (Magnified 1,000 times).
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Phylum: Nematomorpha
Nematomorpha (sometimes called Gordiacea, and commonly known as horsehair
worms or Gordian worms) are a phylum of parasitoidanimals superficially morphologically
similar to nematode worms, hence the name. They range in size in most species from 50 to
100 centimetres (20 to 39 in) long,threadlikeand can reach in extreme cases up to 2 metres,
and 1 to 3 millimetres (0.039 to 0.12 in) in diameter (Fig.32 and 33).
Fig.32. Horsehair Worm (Nematomorpha) and Pterostichus tareumiutbeetleparasitized by
horse hairworm (Nematomorpha)parasite.
Fig.33. FemaleGordionussp. emerging from anAmara alpine(Carabidae: Coleoptera)and a
laboratory over infected variable field cricket,Gryllus lineaticeps withParagordius varius.
Horsehair worms can be discovered in damp areas such as watering troughs,
swimming pools, streams, puddles, and cisterns. The adult worms are free living, but the
larvae are parasitic on beetles, cockroaches, orthopterans, and crustaceans. About 351
freshwater species are known and a conservative estimate suggests that there may be about
2000 freshwater species worldwide. The name "Gordian" stems from the legendary Gordian
knot. This relates to the fact that Nematomorpha often tie themselves in knots.
Examples:Paragordius, Gordius, Nectonema etc.
Nematomorphs possess an external cuticle without cilia. Internally, they have only
longitudinal muscle and a non-functional gut, with no excretory, respiratory or circulatory
systems. The nervous system consists of a nerve ring near the anterior end of the animal, and
a ventral nerve cord running along the body (Fig.34).
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Fig.34. Structure of Paragordius, a nematomorph. A, Longitudinal section through the anterior
end. B, Transverse section. C, Posterior end of male and female worms. Nematomorphs, or
“horsehair worms,” are very long and very thin. Their pharynx is usually a solid cord of cells
and is nonfunctional. Paragordius, whose pharynx opens through to the intestine, is unusual in
this respect and also in the possession of a photosensory organ (“eye”).
(iii)Subdivision: Schizocoelous Coelomata
Coelom is a schizocoel which originates as a space by the splitting of the embryonic
mesoderm.
Phylum: Priapulida
Priapulida (priapulid worms or penis worms, from Gr. πριάπος, priāpos 'Priapus' +
Lat. -ul-, diminutive) is a phylum of marine worms (Fig.35). The name of the phylum relates
to the Greek god of fertility, because their general shape, and their extensible spiny introvert
(eversible proboscis) may recall the shape of a penis. Priapulida are found in colder waters at
a variety of depths from tidal to abyssal. They live in the mud, which they eat, in
comparatively shallow waters up to 90 metres (300 ft). Some species show a remarkable
tolerance for hydrogen sulfide and anoxia.
Priapulids are cylindrical worm-like animals, ranging from 0.2 - 0.3 to 39 centimetres
(0.08 - 0.12 to 15.35 in) in length, with a median anterior mouth quite devoid of any armature
or tentacles. The body is divided into a main trunk or abdomen and a somewhat swollen
proboscis region ornamented with longitudinal ridges. The body is ringed and body surface is
covered with spines and tubercles, which are continued into the slightly protrusible pharynx.
Some species may also have a tail or a pair of caudal appendages. The body has a chitinous
cuticle that is moulted as the animal grows.Their body cavity has a mesodermal lining, so
they can be regarded as coelomate; however the lining is unlike that of other coelomates.
Proboscis anterior and peritoneum of coelom greatly reduced. Circular and longitudinal
muscles exert the pressure required to evert the head region (Fig. 37). The larvae move
through the sediment using their head region as an anchor, but adults are rarely good
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burrowers. They are predators feeding on slow-moving animals, especially worms. At present
only about 16 species of Priapulida have been described, though fossil evidence dates back to
the Cambrian period. Example:Pripulus.
Fig.36. Priapulid worm Priapulus caudatus in a Petry dish.Fig.37.Priapulus bicaudatus.
Phylum: Sipunculida
The Sipuncula or Sipunculida (common names sipunculid worms or peanut
worms) is a group containing 144-320 species (estimates vary) of bilaterally symmetrical,
unsegmentedmarine worms. Traditionally considered a phylum, molecular work suggests that
they might be a subgroup of phylum Annelida.
Fig.38. Sipunculid or peanut worm.
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Sipunculids are all marine and are relatively common, and live in shallow waters,
either in burrows or in discarded shells like hermit crabs do. Some bore into solid rocks to
make a shelter for themselves. Although typically less than 10 cm long, some sipunculans
may reach several times that length.
Sipunculans are worm-like animals ranging from 2 to 720 millimetres in length, with
most species being less than 10 centimetres. The sipunculan body is elongated and cylindrical
with retractile anterior end. Lobes or tentacles are around the mouthand anus is on dorsal
side.The body is divided into an unsegmented trunk and a narrower, retractable anterior
section, called the "introvert". Sipunculans have a body wall somewhat similar to that of
annelids (though unsegmented) in that it consists of a non-ciliated epidermis overlain by a
cuticle, an outer layer of circular and an inner layer of longitudinal musculature. The body
wall surrounds the coelom that is filled with fluid on which the body wall musculature acts as
a hydrostatic skeleton to extend or contract the animal. When threatened, Sipunculids can
retract their body into a shape resembling a peanutkernel - a practice that has given rise to the
name "peanut worm". The introvert is retractable into the trunk via two pairs of retractor
muscles that extend as narrow ribbons from the trunk wall to attachment points in the
introvert. The introvert can be protruded from the trunk by contracting the muscles of the
trunk wall, thus forcing the fluid in the body cavity forwards.Examples: Sipunculus,
Aspidosiphon.
Fig.39. A bucket of deliciously-looking purple worms 'Sand worms' from Beihai.
Sipunculids are capable of regenerating lost parts of their tentacles, introvert, trunk,
or internal digestive system. Some species are able to "clone" themselves by breaking into a
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large front portion and a smaller back portion, each capable of regrowing their missing parts,
and resulting in two separate organisms. To reproduce, sipunculids release their sex cells into
the surrounding water to produce free-swimming juveniles.
Fig.10. A dish of Sipunculid worm jelly made with Sipunculus nudus.
Phylum: Mollusca
Mollusca are one of the most diverse groups of animals on the planet, with at least
50,000 living species (and more likely around 200,000). It includes such familiar organisms
as snails, octopuses, squid, clams, scallops, oysters, and chitons. Mollusca also includes some
lesser known groups like the monoplacophorans, a group once thought to be extinct for
millions of years until one was found in 1952 in the deep ocean off the coast of Costa Rica.
Molluscs are a clade of organisms that all have soft bodies which typically have a
"head" and a "foot" region. Often their bodies are covered by a hard exoskeleton, as in the
shells of snails and clams or the plates of chitons.
A part of almost every ecosystem in the world, molluscs are extremely important
members of many ecological communities. They range in distribution from terrestrial
mountain tops to the hot vents and cold seeps of the deep sea, and range in size from 20meter-long giant squid to microscopic aplacophorans, a millimeter or less in length, that live
between sand grains.
These creatures have been important to humans throughout history as a source of
food, jewelry, tools, and even pets. Besides having yummy soft parts, molluscs often have
desirable hard parts. The shells of some molluscs are considered quite beautiful and valuable.
Molluscs can also be nuisances, such as the common garden snail; and molluscs make up a
major component of fouling communities both on docks and on the hulls of ships.
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They also have a very long and rich fossil record going back more than 550 million
years, making them one of the most common types of organism used by paleontologists to
study the history of life.
Morphology
Despite their amazing diversity, all molluscs share some unique characteristics that
define their body plan. The body has a head, a foot and a visceral mass. This is all covered
with a mantle (also known as a pallium) that typically secretes the shell (Fig.40-44). In some
groups, like slugs and octopuses, the mantle is secondarily lost, while in others, it is used for
other activities, such as respiration.
Fig.40. Snail,Pilasp.
Fig.41. Molluscan internal body parts.
The buccal cavity, at the anterior of the mollusc, contains a radula (lost in bivalves)
— a ribbon of teeth supported by an odontophore, a muscular structure (Fig.42). The radula is
generally used for feeding. The ventral foot is used in locomotion. This foot propels the
mollusc by utilizing muscular waves and/or cilia in combination with mucus(Fig. 43).
Fig.42. The freshwater Sinistral Pond Fig. 43. A cuttlefish, a coleoid
Snail (Physella sp.) scrapes algae from cephalopod,
moves
primarily
by
the glass with its radula, the two undulating its body fins.
"toothy" arcs you can see lining the
mouth.
Typically, at least in the more primitive members of each group, there are one or more
pairs of gills (called ctenidia) which lie in a posterior cavity (the pallial cavity) or in a
posterolateral groove surrounding the foot. The pallial cavity typically contains a pair of
sensory osphradia (for smelling) and is the space into which the kidneys, gonads, and anus
open.
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Molluscs are coelomate, although the coelom is reduced and represented by the
kidneys, gonads, and pericardium, the main body cavity which surrounds the heart.
Examples: Chitons, snails (Pila), mussels (Unio), squids (Loligo), etc.
Fig.44. On the left is a marine snail, the California Trivia (Trivia californiana). Here the mantle
covers much of the shell. Note how a portion of the mantle is rolled into a tube shape to form the
siphon just above the head. At the right is a restoration of one of the largest of all molluscs, the
Giant Squid (Architeuthis).
Phylum: Echiurida
The Echiura, or spoon wormsor adder-tailed worms, are a small group of
marineanimals(Fig.45). Once treated as a separate phylum, they are now universally
considered to represent derived annelid worms. The Echiura fossilise poorly and the earliest
known specimen is from the Upper Carboniferous (called the Pennsylvanian in North
America). However, U-shaped fossil burrows that could be Echiuran have been found dating
back to the Cambrian.
Fig.45. (a)Echiurussp. entire animal (ant.set, anterior setae; post.set, posterior setae;prob,
proboscis);(b) Echiurus sp. showing an extensible proboscis and posterior end with a set of small
hooks; (c)Echiuran long and coiled intestines.
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Echiurans have a worm-like body with a large flattened proboscis projecting forward
from the head (Fig.45 and 46). The body is typically drab in colour, but bright red and green
species are known. Its body is cylindrical with anterior retractile proboscis. Its trunk is with
setae. The proboscis is a sheet-like structure, rolled around into a cylindrical tube with an
open gutter at the ventral surface. The length of the proboscis varies greatly between species,
and in some species is many times longer than the rest of the body. It is probably homologous
with the prostomium of other annelids.
Fig.46. Echiura Urechis unicinctuson a market in South Korea.
Compared with other annelids, echiurans have relatively few setae. In most species,
there are just two, located on the underside of the body just behind the proboscis. In others,
such as Echiurus, there are also further setae near the posterior end of the animal. Unlike
other annelids, adult echiurans have no trace of segmentation.
Echiurans are marine worms similar in size and habit to sipunculans. Many genera,
such as Echiurus, Urechis, and Ikeda, live in burrows in sand and mud; others live in rock
and coral crevices. One species, Thalassema mellita, which lives off the southeastern coast of
the US, inhabits the tests (exoskeleton) of dead sand dollars. When the worm is very small, it
enters the test and later becomes too large to leave.
The majority of echiurans live in shallow water, but there are also deep sea forms.
More than 230 species have been described.[
Phylum: Annelida
The annelids (also called "ringed worms"), formally called Annelida (from
Latinanellus "little ring", are a large phylum of segmented worms including ragworms,
earthworms and leeches (Fig.47). They are found in marine environments from tidal zones to
hydrothermal vents, in freshwater, and in moist terrestrial environments. They are bilaterally
symmetrical, triploblastic, coelomate organisms. They have parapodia for locomotion. There
are over 22,000 living annelid species, ranging in size from microscopic to the Australian
giant Gippsland earthworm and Amynthas mekongianus (Cognetti), which can both grow up
to 3 metres long.
The basic annelid form consists of multiple segments, each of which has the same sets
of organs and, in most polychaetes, a pair of parapodia that many species use for locomotion.
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Septa separate the segments of many species, but are poorly-defined or absent in some, and
Echiura and Sipuncula show no obvious signs of segmentation. In species with welldeveloped septa, the blood circulates entirely within blood vessels, and the vessels in
segments near the front ends of these species are often built up with muscles to act as hearts.
The septa of these species also enable them to change the shapes of individual segments,
which facilitates movement by peristalsis ("ripples" that pass along the body) or by
undulations that improve the effectiveness of the parapodia. In species with incomplete septa
or none, the blood circulates through the main body cavity without any kind of pump, and
there is a wide range of locomotory techniques - some burrowing species turn their pharynges
inside out to drag themselves through the sediment.
Fig.48.
Fig.47.
Fig.11. Bloodworm, Glycera sp., abounds in salt marsh sediments.
Fig.12. Bamboo worm(Capitella capitata F.).
Fig.50
Fig.49. Calcareous tubeworm, fan worm, plume
worm or red tube worm(Serpula vermicularis L.)
Fig.51.Nereis pelagica.Fig.51. Rag worm,
clamworm or Nereid worm-Live Nereissp.
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Fig. 52.
Fig.52.Hediste diversicolor.
Fig.53. Lamellibrachia luymesi
Fig.54. Amynthas sp., a common Asian earthworm often cosmopolitan and introduced
around the world
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Fig. 55.Earthworms mating.
Fig. 56. Cocoons of earthworms, L. rubellus.
Fig. 57. Earthworms’faeces in form of casts.
Fig. 58. Earthworm (L. terrestris) -
permanent vertical burrow.
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Although many species can reproduce asexually and use similar mechanisms to
regenerate after severe injuries, sexual reproduction is the normal method in species whose
reproduction has been studied. The minority of living polychaetes whose reproduction and
lifecycles are known produce trochophore larvae, which live as plankton and then sink and
metamorphose into miniature adults. Oligochaetes are full hermaphrodites and produce a
ring-like cocoon round their bodies, in which the eggs and hatchlings are nourished until they
are ready to emerge.
Earthworms support terrestrial food chains both as prey and by aerating and enriching
soil (Fig.59). The burrowing of marine polychaetes, which may constitute up to a third of all
species in near-shore environments, encourages the development of ecosystems by enabling
water and oxygen to penetrate the sea floor.
Fig. 59. Staphylinus olens fighting an earthworm
(Lumbricus sp.) near Nettersheim, Germany.
Fig. 60.A close up of an earthworm in garden soil.
In addition to improving soil fertility, annelids serve humans as food and as bait.
Scientists observe annelids to monitor the quality of marine and fresh water. Although bloodletting is no longer in favor with doctors, some leech species are regarded as endangered
species because they have been over-harvested for this purpose in the last few centuries.
Leeches have been used to treat patients for centuries. Leech therapy, which is called in
Ayurveda system as Jalauka or Rakta Moksha, is an old form of Ayurvedic detoxification
with the help of the creeping insect leech. Ayurvedic scriptures such as Charak Samhita and
the Sushrut Samhita give many details of this therapy. The impure blood which is the root
cause of most of the human ailments is removed from the body. Leeches have the ability to
suck blood clotted around muscles or skin (Fig.61). The anti-blood clotting enzymes in their
saliva make the blood circulation normal. In this way, leech therapy does wonders in many
diseases connected with blood clotting.There are approximately 600 leech species which have
been identified to date but only about 15 are used in medicine.Leech therapy has been used
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in European countries since 18th and 19th centuries. Today, doctors use leeches for treating
abscesses, painful joints, glaucoma, myasthenia, and to heal venous diseases and thrombosis.
Medical leeches are used in plastic surgery, for improving brain circulation and for curing
infertility. Some even claim that this could be an alternative acne treatment (Fig.65). In
Fig.62 the leeches hanging from the chin of a Kashmiri womanare shown, who is undergoing
a leech therapy session at a roadside in Srinagar, Kashmir, India during summer. Leeches,
which are widely used to promote bloodletting, are being used to heal pain and other ailments
in Kashmir.Even with osteoarthritis of the knee joint, a leech therapy may be effective
(Fig.63.). Painful, locally jammed and metabolically abnormal processes can be treated this
way. Most common use of leech therapy is in local inflammation, arthritis and chronic pain
syndromes (Fig. 64 and 65). Potentially, this could be a business opportunity for those who
are interested in alternative medicine (Fig.66).
Fig.61. Leech Therapy: An alternative therapy for cancer.
Fig.63. Leech therapy for osteoarthritis.
Fig.62. Leech therapy session in
Kashmir, India.
Fig.64. Leech therapy session in Kashmir,
India.
In tropical regions, leech bites on the skin are commonly encountered, especially,
when people walk carelessly through bushes and water (Fig.67).
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Fig. 65. Russian woman takes
treatment in a laboratory in Moscow.
leech Fig.66.Booming leech trade raises concerns.
Vaginal leech bites, in children are also commonly heard in rural part of north-eastern
India. Leeches have been reported in body cavities open to and nearer to the exterior. We
report a 2-year- old girl with intraperitoneal leech. The leech entered her vagina and uterus,
perforated the uterus and entered into the peritoneal cavity (Fig.68 and 69).
Fig. 67. Leech attacks on the legs of men.
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Fig.68: Leech popping out from the pelvic
cavity.
Fig.69: Postoperative leech specimen.
The marine annelid (Nereis)is used to derive biopesticide which is the only pesticide
of animal origin (Fig.70). Cartap Hydrochloride(Imidacloprid) is an analogue or pro-Crop
Protection product of the natural toxinNereis. It is a systemic insecticide with stomach and
contact action.
Fig.70. External body features of ragworm, Nereis sp. (dorsal view).
Ragworms' jaws are now being studied by engineers as they offer an exceptional
combination of lightness and strength. Examples: Earth worms, Nereis, Leech, etc.
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Phylum: Tardigrada
The name water bear comes from the way they walk, reminiscent of a bear's gait. The
biggest adults may reach a body length of 1.5 millimetres; the smallest below 0.1 mm. The
freshly hatched tardigrades may be smaller than 0.05 mm.
About 1,150 species of tardigrades have been described. Tardigrades occur
throughout the world, from the Himalayas (above 6,000 metres), to the deep sea (below 4,000
metres and from the polar regions to the equator.
Tardigrades (commonly known as water bears or moss piglets) are small, waterdwelling, segmented micro-animals with eight legs.Body segmented with pairs of
unsegmented legs terminates in claws.Usually, tardigrades are 1 millimetre long when they
are fully grown. They are short and plump with 4 pairs of legs, each with 4-8 claws also
known as "disks."The animals live in freshwater, terrestrial and marine ecosystem and are
prevalent in moss and lichen and, when collected, may be viewed under a very low-power
microscope. The diagram showing internal and external body features and electron
micrograph showing features and colour of different species are given in Fig.71-78.
Tardigrades are notable for being one of the most complexes of all known
polyextremophiles. An extremophile is an organism that can thrive in a physically or
geochemically extreme condition that would be detrimental to most life on Earth. For
example, tardigrades can withstand temperatures from just above absolute zero to well above
the boiling point of water, pressures about 6 times stronger than pressures found in the
deepest ocean trenches, ionizing radiation at doses hundreds of times higher than would kill a
person, and the vacuum of outer space. They can go without food or water for more than 10
years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and
reproduce. Examples: Macrobiotus hufelandi, Echiniscussp., Hyphsibussp., etc.
Fig. 71. Macrobiotus hufelandi. I-IV,
appendages; b. c, buccal cavity; gl,
accessory gland; mal, Malphigian
tube; ov, ovary; ph, pharynx; r,
rectum; sal.gl, salivary glands; st,
stomach; t, teeth.
Fig. 72. Echiniscus sp.
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Fig. 75. Echiniscus testudo Doyère,
Fig. 73. Water bear (tardigrade), Hypsibius
dujardini, scanning electron micrograph.
Fig.76.Coloured scanning micrograph of a
marine tardigrade (Macrobiotus sp.)
showing 4 pairs of stumpy legs terminating
in claws for clinging to sand or soil.
Fig.77.
Coloured
scanning
electron
micrograph of a water bear (Echiniscus
testudo) in its crypto-biotic tun, or barrel,
state.
Fig.74. Giant yellow water bear (Richtersius
coronifer); 2. Large carnivorous water bear
(Milnesium tardigradum); 3. Tidal water bear
(Echiniscoides sigismundi sigismundi); 4. Turtle
water bear (Echiniscus testudo); 5. Balloon water
bear (Tanarctus bubulubus).
Fig.78.Pseudobiotus sp.
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Phylum: Onychophora
The velvet worms (Onychophora — literally "claw bearers", also known as
Protracheata) are a minor ecdysozoanphylum with ~180 species. These obscurely
longsegmented organisms have tiny eyes, a pair of anteriorantennae, multiple pairs of
shortlegs ending in clawsand slime glands. Body surface with thin cuticle and live in moist
terrestrial. ecosystem. Examples: Peripatopsis, Peripetus.They have variously been
compared to worms with legs, caterpillars and slugs. Most common in tropical regions of the
Southern Hemisphere, they prey on smaller animals such as insects, which they catch by
squirting adhesivemucus. In modern zoology, they are particularly renowned for their curious
mating behaviour and for bearing live young.
Fig.79. Peripatoides novaezealandiae clearly showing the stub feet.
Fig. 80. Velvet Worm (Onychophora) from the Amazon Rain Forest in Peru.
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The two existing families of velvet worms are Peripatidae and Peripatopsidae. They
show a peculiar distribution, with the peripatids being predominantly equatorial and tropical,
while the peripatopsids are all found in what used to be Gondwana.
A
B
Fig.81.A. Cephalofovea tomahmontis. B. Epiperipatus biolleyi.
Phylum: Arthropoda: (Joint- footed animals).
This is the largest and most successful of the animal phyla, with over 1 000 000
species identified to date and an estimated 1 000 000 000 000 000 000 (1 quintillion)
individuals alive today. Some scientists estimate that there are over 200 million insects for
each single person. That's just insects alone, and doesn't include the countless millions of
spiders, crustaceans, millipedes, centipedes, etc that make up the phylum Arthropoda.
Arthropods are the most easily identifiable of all the animals, as they all share several
things in common that no other animals share. First, all arthropods are protected by a hard
exoskeleton (outer skeleton) composed of chitin (humans and other chordates have
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endoskeletons). This exoskeleton protects the organs, gives support for the body, and allows
for efficient locomotion. However, because the exoskeleton cannot grow, it must periodically
be shed to allow for the organism to grow.
1
2
3
4
5
6
Fig.82. (1) Kolihapeltis, (2) Stylonurus, (3) Scorpion, (4) Crab, (5) Centipede, (6) Butterfly.
All arthropods have segmented bodies divided into a head, thorax, and abdomen. In
some cases, such as with the lobster, the head and thorax are fused together. This is called a
cephalothorax. Arthropods also have jointed appendages.
Arthropods have a complex internal design, with ganglia for a brain and an organ that
acts as a heart. They have a complete digestive and excretory system. They also have welldeveloped sensory organs, that include antennae, eyes, and in some cases internal ears.
Respiration occurs through the body surface, gills, trachea, and/or book lungs. The oxygen is
carried in an open circulatory system (humans have a closed circulatory system).
Arthropods are very diverse, and therefore can locomote in a wide variety of ways.
They can walk, crawl, climb, hop, fly, glide, swim, skate, dive - almost every type of
locomotion imaginable (other than drive!).
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Arthropods can be found on every continent and in every ocean, from the harsh
climate of Antarctica to the dryness of the desert to the dampness of the rainforests, and even
to the darkness of the ocean's depths. They can be found in ponds, on plants, in and on other
animals, and even in your own house!Examples:Scorpions, prawns, flies, centipedes, etc.
Phylum: Pentastomida
Pentastomida are an enigmatic group of parasiticinvertebrates commonly known as
tongue worms due to the resemblance of the species of the genus Linguatula to a vertebrate
tongue.Alternative names for the Pentastomida include Pentastoma (strictly a genus name),
Linguatulida, and Acanthotheca Examples: Porocephalus, Cephalobaena etc.
There are about 130 extant species of pentastomids; all are obligate parasites with
correspondingly degenerate anatomy. Adult tongue worms vary from about 1 to 14
centimetres in length, and parasitize the respiratory tracts of vertebrates. They have five
anterior appendages. One is the mouth; the others are two pairs of hooks which they use to
attach to the host. This arrangement led to their scientific name, meaning "five openings", but
although the appendages are similar in some species, only one is a mouth.
Pentastomids are worm-like animals with two anterior appendages terminating in
claws and ranging from 2 to 13 centimetres in length. The anterior end of the body bears five
protuberances, four of which are clawed legs, while the fifth bears the mouth. The body is
segmented and covered in a chitinous cuticle. The digestive tract is simple and tubular, since
the animal feeds entirely on blood, although the mouth is somewhat modified as a muscular
pump (Fig.83 and 84). These are blood sucking endoparasites of vertebrates.
The nervous system is similar to that of other arthropods, including a ventral nerve
cord with ganglia in each segment. Although the body contains a haemocoel, there are no
circulatory, respiratory, or excretory organs
Fig.84. Adult female Linguatula
serrata.
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Subdivision(iv): Lophophorate Coelomata
Coelom develops as schizocoel or enterocoel and with a crown of hollow tentacles
(Lophophore) surrounding the mouthy. Head indistinct. Gut U- shaped.
Phylum: Phoronida
The Phoronida is one of the smallest and least familiar phyla; there are about twenty
species in two genera, Phoronis and Phoronopsis. However, phoronids -- or "horseshoe
worms," as they are sometimes called -- may be abundant in shallow marine sediments at
certain localities. Phoronids are elongated and worm-shaped, but the gut loops and ends close
to the mouth, instead of passing straight through the body as in annelids and many other
wormlike organisms (Fig.85 and 86).The mouth is surrounded by the ciliated feeding
structure known as a lophophore. The lophophore of phoronids is a simple ring in some
species, folded into a horseshoe shape in others, as shown in Phoronopsis
viridis(Fig.87)(hence the common name "horseshoe worms"), and coiled in other species.
Fig.86. Phoronid secreted tubesof
agglutinated sedimentas shown
around their bodies.
Fig.87.The horseshoe shape lophophore of a phoronid (Phoronopsis viridis).
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They are found in all oceans and seas (except the polar seas), and all species have
wide geographical ranges.They occur at depths up to 400 metres, but mainly between 0 to 70
metres. The life span is thought to be about a year. The adults are tube worms, and secrete
chitinous tubes in which they live. These tubes can be buried in the mud or sand or rest on the
surface of a rocky substrate. If on rocks, they may live in colonies with their tubes become
twisted around each other for support. Some species can dissolve away holes in rocks such as
limestone, calcareous seashells or even cementpiers; they then live in these holes which they
line with their secreted tubesof agglutinated sediment, as shown in Fig.86, around their
bodies. Though they are normally long, up to 50cm. Phoronids are normally very
thin.Examples: Phoronis, Phoronopsis etc.
They feed using a lophophore, a ciliated structure that surrounds the mouth. Phoronids
are suspension-feeders. They move their lophophores into the prevailing water current. Food
particles in the water current are trapped in a stream of mucous that travels along the tentacles
until it reaches the oral ring. There it is drawn into the mouth and then on into the digestive
tract. Direct uptake of amino acids through the epidermis also occurs.
Phylum: Bryozoa or Ectoprocta
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a
phylum of aquatic invertebrate animals. Typically about 0.5 millimetres long, they are filter
feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of
tentacles lined with cilia. Most marine species live in tropical waters, but a few occur in
oceanic trenches, and others are found in polar waters. One class lives only in a variety of
freshwater environments, and a few members of a mostly marine class prefer brackish water.
Over 4,000 living species are known. One genus is solitary and the rest colonial.Examples:
Bugula, Plumatella, etc.
Fig.88. Bugula flabellate colony
hanging from rock race.
Fig.89. A marine colony of Bryozoa.
Phylum: Brachiopoda
The word "brachiopod" is formed from the Ancient Greek words βραχίων ("arm") and
πούς ("foot"). They are often known as "lamp shells", since the curved shells of the
classTerebratulida look rather like pottery oil-lamps.Brachiopoda (from Latin bracchium,
arm + New Latin -poda, foot) is a major invertebrate phylum, whose members, the
brachiopods, are sessile, two-shelled, marine animals with an external morphology
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resembling bivalves (that is, "clams") of phylum Mollusca to which they are not closely
related. Brachiopods are found either attached to substrates by a structure called a pedicle or
unattached and resting on muddy bottoms. Brachiopods are suspension feeders with a
distinctive feeding organ called a lophophore found only in two other suspension-feeding
animal phyla, the Phoronida (phoronid worms) and the usually colonial Ectoprocta or
Bryozoa. Characterized by some as a "crown" of ciliated tentacles, the lophophore is
essentially a tentacle-bearing ribbon or string that is an extension (either horseshoe-shaped or
circular) surrounding the mouth.Examples: Lingula, Crania, etc.
1
2.
Fig.90. Lamp shells:1. Kraussina mercatori; 2.Pajaudina atlantica.
Fig.913. Spiriferina rostrata with visibleskeleton of the lophophore.
Division 2: Deuterostomia
Mouth arises some distance away from blastopore.
Subdivision: Enterocoelous Coelomata
Coelom is an enterocoel which originates as pouches of embryonic gut (archenteron).
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Phylum: Chaetognatha (Arrow worms).
Chaetognatha, meaning bristle-jaws, and commonly known as arrow worms, are a
phylum of predatory marine worms that are a major component of plankton worldwide.
About 20% of the known species are benthic, and can attach to algae and rocks. They are
found in all marine waters, from surface tropical waters and shallow tide pools to the deep
sea and Polar Regions. Most chaetognaths are transparent and are torpedo shaped, but some
deep-sea species are orange. They range in size from 2 to 120 millimetres (0.079 to
4.7 in).They have small elongated body bearing fins and anterior end with grasping spines.
There are more than 120 modern species assigned to over 20 genera. Despite the
limited diversity of species, the number of individuals is large. Examples: Sagitta, Spadella,
etc.
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Phylum: Echinodermata
Echinodermata (əkī´nōdûr´mətə) [Gr.,=spiny skin], phylum of exclusively marine
bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the
skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to
facilitate movement, as in sea stars (starfish), or reduced to minute spicules in the skin, as in
sea cucumbers. The skin usually has warty projections or spines, or both. Echinoderms
display pentamerous radial symmetry, that is, the body can be divided into five more or less
similar portions around a central axis. Unlike other radially symmetrical animals, they
develop from a bilaterally symmetrical larva and retain some degree of bilateral symmetry as
adults. There is no head; the surface containing the mouth (the underside, in sea stars and
most others) is called the oral surface, and the opposite side, which usually bears the anus, the
aboral surface. There are five living classes of echinoderms.
There are a total of about 7,000 extant species of echinoderm as well as about 13,000
extinct species. They are found in habitats ranging from shallow intertidal areas to abyssal
depths.Spiny-skinned animals, about 6,000 species, secondarily pentamerous radial
symmetry. A part of coelom as water vascular canals. Locomotion by tube feet. Examples:
Brittle stars, starfish, sea urchins, sea lilies, etc.
1
2
3
4
Fig.95.1. Sea urchin (Strongylocentrotus purpuratus);
2.Ruby brittle star or brain coral (Ophioderma rubicundum);
3. Echinaster sepositus;4. Sea lilies or feather star (Crinoidea).
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Phylum: Pogonophora
The name Pogonophora is Greek for "beard-bearers," and comes from the fact that
many species have from one to many tentacles at the anterior end. These tentacles somewhat
resemble the lophophore found in animals like brachiopods and bryozoans, as well as the
feeding tentacles of certain chordates. The incompletely known anatomy of pogonophorans
was interpreted to show that pogonophorans were chordate relatives. Because pogonophorans
live with their lower ends buried in mud, and were broken during the dredging process, it was
not until 1964 that a complete pogonophoran was recovered. It turned out that pogonophorans
have a segmented posterior end of the body -- the opisthosoma -- that bears setae and
resembles an annelid body. The forward part of the body, or prosoma, is unsegmented.
Because of the segmented opisthosoma, and because pogonophoran larvae have been found
to look very much like annelid larvae, pogonophorans are now considered to be close
relatives of the annelids, and are classified with them in a larger group, the Trochozoa.
1
2
Fig.98. Pogonaphora: 1.Lamellibrachia luymesi van der Land and Nørrevang;
2. Riftia pachyptila Jones.
About 80 pogonophoran species are known today, with new species still being
discovered. One of the most spectacular zoological discoveries of recent years was the
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finding in 1977 of giant pogonophoran worms, 1.5 meters long, growing in heated, sulfurrich water around warm-water vents in the Pacific Ocean, 2600 meters below the surface
(pictured at right). These worms are sometimes placed in their own phylum, the
Vestimentifera, but they are similar to pogonophorans in most respects, and the current
tendency is to group these rift-dwelling worms together with the rest of the Pogonophora into
one phylum.
Phylum: Hemichordata
Hemichordates ("half (½) chordates") have some features similar to those of
chordates: branchial openings that open into the pharynx and look rather like gill slits;
stomochords, similar in composition to notochords, but running in a circle round the "collar",
which is ahead of the mouth; and a dorsal nerve cord - but also a smaller ventral nerve cord.
There are two living groups of hemichordates. The solitary enteropneusts, commonly
known as "acorn worms", have long proboscises and worm-like bodies with up to 200
branchial slits, are up to 2.5 metres long, and burrow though seafloor sediments. Pterobranchs
are colonial animals, often less than 1 millimetre long individually, whose dwellings are
interconnected. Each filter feeds by means of a pair of branched tentacles, and has a short,
shield-shaped proboscis. The extinct graptolites, colonial animals whose fossils look like tiny
hacksaw blades, lived in tubes similar to those of pterobranchs.
Hemichordata is a phylum of marine deuterostomeanimals, generally considered the
sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include
two main classes: Enteropneusta (acorn worms), and Pterobranchia. A third class,
Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera
pelagica. The extinct class Graptolithina is closely related to the pterobranchs.
Fig.99. Acorn worm, a hemichordate.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Fig.14. Body parts of acorn worm.
Acorn worms are solitary worm-shaped organisms. They generally live in burrows
(the earliest secreted tubes) and are deposit feeders, but some species are pharyngeal filter
feeders. Many are well known for their production and accumulation of various halogenated
phenols and pyrroles. Pterobranchs are filter-feeders, mostly colonial, living in a collagenous
tubular structure called a coenecium.
The body plan of hemichordates is characterized by a tripartite organization. The
anteroposterior axis is divided into three parts: the anterior prosome, the intermediate
mesosome, and the posterior metasome.
The body of acorn worms is worm-shaped and divided into an anterior proboscis, an
intermediate collar, and a posterior trunk. The proboscis is a muscular and ciliated organ used
in locomotion and in the collection and transport of food particles. The mouth is located
between the proboscis and the collar. The trunk is the longest part of the animal. It contains
the pharynx, which is perforated with gill slits (or pharyngeal slits), the esophagus, a long
intestine, and a terminal anus. It also contains the gonads.
The prosome of pterobranchs is specialized into a muscular and ciliated cephalic
shield used in locomotion and in secreting the coenecium. The mesosome extends into one
pair (in the genus Rhabdopleura) or several pairs (in the genus Cephalodiscus) of
tentaculated arms used in filter feeding. The metasome, or trunk, contains a looped digestive
tract, gonads, and extends into a contractile stalk that connects individuals to the other
members of the colony, produced by asexual budding. In the genus Cephalodiscus, asexually
produced individuals stay attached to the contractile stalk of the parent individual until
completing their development. In the genus Rhabdopleura, zooids are permanently connected
to the rest of the colony via a common stolon system.
They have a diverticulum of the foregut called a stomochord, previously thought to be
related with the chordate notochord, but this is most likely the result of convergent evolution
rather than homology. A hollow neural tube exists among some species (at least in early life),
probably a primitive trait they share with the common ancestor of chordata and the rest of the
deuterostomes.
Some species biomineralize in calcium carbonate.
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
Phylum: Chordata
Chordates, members of the phylumChordata, are deuterostomeanimals possessing a
notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail for
at least some period of their life cycles. Taxonomically, the phylum includes the subphyla
Vertebrata, including mammals, fish, amphibians, reptiles, birds; Tunicata, including salps
and sea squirts; and Cephalochordata, comprising the lancelets. Primitive chordates are
known from at least as early as the Cambrian explosion.
There are more than 75,000 living species of chordates, about half of which are bony
fish of the class osteichthyes. The world's largest animal, the blue whale, and fastest animal,
the peregrine falcon, are chordates, as are humans,snakes, birds, Ascidians, Amphioxus,
fishes, frogs, rabbit, etc.
Subphylum: Urochordata
The tunicates are marine, filter-feeding animals (Fig. 102). The most prominent
tunicates are the sea squirts (class Ascidiacea), which show affinities to other chordates only
in the juvenile stage. Adult sea squirts are sessile (attached), globular or tubular animals,
often with prominent incurrent and excurrent siphons; many kinds grow in colonies. Most of
the body of the adult is occupied by a very large pharynx with numerous gill slits that act as a
sieve for food. Water taken into the incurrent siphon enters the pharynx and passes out
through the gill slits, leaving food particles trapped in the pharynx. A groove in the pharynx
called the endostyle secretes mucus that traps the particles and conveys them into the
digestive tract; the movement of the mucus is caused by the action of cilia. Water leaves the
atrium, a sac surrounding the pharynx, by way of the excurrent siphon. Thus the gill slits in
tunicates serve a feeding function, not a respiratory function.
The sea squirt larva is a free-swimming animal resembling a tadpole. The head, which
will become the entire body of the adult, contains a rudimentary brain and sense organs, a
small pharynx and digestive tract, and a ventral heart. Incurrent and excurrent openings are
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
located at the top of the head. The tail is a muscular appendage that functions as a swimming
organ. It contains a hollow nerve tube (connected to the brain), and a notochord that extends
into the head and keeps the animal from telescoping when its muscles contract. When the
larva is ready to undergo metamorphosis it attaches to an object head downward. The tail,
notochord, and nerve cord degenerate, the pharynx enlarges, and the other organs shift in
position; the incurrent and excurrent openings develop siphons.
Fig.102. A colony of sea tulips -
There are two other classes of tunicates, both consisting of small planktonic animals.
The salps (Thaliacea) metamorphose into barrel-shaped adults that swim by muscular
contractions. The larvaceans (Larvacea) are neotenous, that is, they achieve sexual maturity
and reproduce without losing the larval form. Many zoologists believe that tunicates of the
sea squirt type were the first chordates and that the larval tail, with its notochord and nerve
chord, was evolved as a means of dispersing their larvae. According to this theory, the later
chordates, including the vertebrates, are descended from neotenous tunicates that, like the
larvaceans, failed to assume the adult form.
Subphylum Cephalochordata
This class includes the several species of lancelets (Fig. 103), or amphioxi, small,
fishlike, filter-feeding animals found in shallow water. A lancelet has a long body, pointed at
both ends, with a large notochord that extends almost from tip to tip and is present throughout
life. At one end is a mouth surrounded by prominent bristles and leading into a pharynx. The
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
pharynx has gill slits, an endostyle similar to that of a sea squirt, and an atrium surrounding
the pharynx. Water enters the mouth and leaves through the gill slits, and food is trapped in
the pharynx. The dorsal, tubular nerve cord is slightly enlarged in the anterior region, forming
a rudimentary brain. Nerves extend from the nerve chord to other parts of the body. The
muscles, as in fishes, are a series of cone-shaped blocks that fit into each other like stacked
paper cups. This is the most primitive occurrence of the segmental body wall structure
characteristic of lower vertebrates. The colorless blood moves forward through a ventral
vessel and back through a dorsal vessel, in the typical chordate pattern. There is no major
heart, although many small enlargements of the vessel serve the function of hearts. There are
no blood cells and no respiratory pigments. The excretory system, like that of many
invertebrates, consists of segmentally arranged nephridia; there is no kidney. The gonads,
unlike those of any other chordate, are numerous and segmentally arranged.
Fig.103.ALancelet (or Amphioxus) specimen (Branchiostoma lanceolatum)collected in coarse sand
sediments (600 µm) on the Belgian continental shelf.
Subphylum: Vertebrata
Vertebrates constitute the vast majority of living chordates, and they have evolved an
enormous variety of forms (Fig.104). The backbone of vertebrates protects the nerve cord and
serves as the axis of the internal skeleton. The skeleton provides strength and rigidity to the
body and is an attachment site for muscles. The vertebrae in the middle region of the trunk
give rise to pairs of ribs, which surround and protect the internal organs. A cartilaginous or
bony case encloses the brain. Bone is a substance unique to vertebrates. It was formerly
thought that vertebrates with cartilage skeletons (cyclostomes and shark like fishes) were
descended from early vertebrates that had not yet developed bone. However, very primitive
fishes with bone skeletons are known from the fossil record, so lack of bone is now believed
to be a degenerate rather than a primitive feature. All but the most primitive vertebrates,
known as jawless fishes, have jaws and paired appendages. The fishes and, to a lesser extent,
the amphibians and reptiles show a segmental arrangement of the muscles of the body wall
and of the nerves leading to them.
There are eight vertebrate classes. Four are aquatic, and may be grouped together as
the superclass Pisces, or fish; four are terrestrial or (in the case of amphibians) semiterrestrial,
and may be grouped as the superclass Tetrapoda, or four-footed animals. Fishes breathe water
by means of gills located in internal passages, although they may also have lungs as
Professor Paras Nath’s Agricultural Biology Lecture Note CAFF, FNU-2013
L 4 ENT 402: Agricultural Biology
supplementary air-breathing organs. Most move through the water by weaving movements of
the trunk and tail. All have fins, and most have two sets of paired fins (pelvic and pectoral).
Tetrapods breath air, usually by means of lungs, and never have gills as adults, although the
amphibians go through a gilled, water-breathing stage. Except where the appendages have
been lost, as in snakes, all have two pairs of limbs, generally used for locomotion; these are
homologous to the pelvic and pectoral fins of fish.
1
2
3
4
5
Fig.104. 1. Fire Salamander (Salamandra salamandra);
2. Saltwater Crocodile(Crocodylus porosus)
3. Southern Cassowary (Casusarius casuarius);
4. Black-and-rufus Giant Elephant Shrew (Rhynchocyon petersi)
5. Ocean Sunfish (Mola mola).
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