Download Chapter 18 - San Diego Mesa College

SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Chapter 18: Evolution of animals, animal kingdom & Animal
life cycles
- Part I 
We humans share the surface of this planet with another highly evolved and mobile
form of life we call animals

According to scientific evidence, animals have been on this planet since a long time
and we humans share many of the animals features, at the molecular, cellular,
physiological and anatomical level

In this chapter we will try to understand the natural history of animals and the
important animal features as well as characteristics which will help us understand
their unique habitats and distribution on this planet
Evolution of animals and prominent members of the animal kingdom

fossil and biochemical evidence tell us, that the earliest forms of biological
organisms, which we call animals, existed already around 700 million years ago
during the late, so-called Precambrian era
- the first animal fossils appear at the end of the Proterozoic age (650 – 544 mya),
also known as the Vendian period
- the first diversification of soft-bodied organisms, collectively known as the
"Vendian fauna" or "Ediacaran fauna“ happened during that time
- scientist are not sure whether these fossilized creatures (see images below)
were algae, lichens, giant protozoans, or even a separate (now extinct) kingdom
of life (!)

most of the modern phyla of the animal kingdom (see classification scheme
below) existed already during the time of the famous Ediacaran fauna which existed
during the Cambrian period approx. 600 million years ago
 the earliest fossils appear around that time

scientists assume, that all “modern members” and still existing life forms of the
animal kingdom arose in the oceans from (a) heterotrophic colony-forming unicellular protist(s) (= protozoan)
- biologists hypothesize, that some of these ancient protist colonies began to fold
inward (see “Gastrulation” further below), creating the first gastrula-like protoanimal
- this view is still hypothetical since no fossils of “proto-animals” have been found
until today

later in this proto-animal stage, cell specialization must have occurred, paving the
way for the evolution of true multi-cellular animals
- the first splitting of functional tasks may have occurred in these early multicellular
colonies
- an early type of specialization amongst these cells may have created the first
somatic and reproductive cells
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SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
-
however, how these proto-animals exactly looked like remains a mystery, since
fossilized structures are very unlikely to arise from their fragile, soft-bodied
bodies
Images of fossils of early animal life forms on Earth
(Age: Cambrian era - approx. 600 million years ago)
Image of original fossil find
Name
Dickinsonia
- phylum ??
Tribrachidiu
- Cnidarian?
- Echinoderm?

scientists believe, that the morphology and features of the very early stages of
embryonic development in animals (see:  the typical animal life cycle with
Blastula, Gastrula stages) may reflect in a certain way the shapes of these “protoanimals”

the ancestral colonial protist that gave rise to the animal kingdom diverged first into
two separate lineages (see Graphic below)
1. the Parazoa (Latin for "false animal")
 contain only one modern phylum, called Porifera, which contains
the sponges
 they are NOT true animals, because they have no true tissues
(= no ectoderm, endoderm nor mesoderm layers)
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SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
2. the Eumatazoa ("true animals")
 the Eumatazoa branch gave rise to all other modern animal phyla
(see Chart of animal phyla below)
 they all have true tissues

the radiation of diversity in the kingdom Animalia proceeded based on the evolution
of a number of distinct "hallmark" features or characteristics
Characteristics of animals

animals are living organisms characterized by 7 main features
1. they are made of eukaryotic cells
2. animals are multicellular organisms
3. animals are heterotrophic organisms
 most animals take up complex food and digest it in specially
formed body cavities, called digestive tract
4. cells have no cell wall
 but have characteristic so-called intercellular junctions
(= connection structures)
5. have characteristic stages during their life cycle, called blastula and gastrula
6. they have true tissues, each with unique physiological functions within the
animal body
7. animals have the capability of mobility at some stage during their life cycle
3
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Taxonomy of important phyla of the animal kingdom & Body characteristics
- Part I Ancestral colonial
protozoan
- hypothetical
- no fossil evidence
Parazoa
Eumetazoa
“false animals”
“true animals”
- have true tissues
Porifera
B ody
symmetry
(Sponges)
- 5000 species
- no true
- no digestive
-tract
no nervous system
Radiolaria
Bilateria
- radial symmetrical
animals
- bilateral symmetrical
animals
Cnidaria
(“Jellyfishes”)
- 10,000 species
- no
- gastrovascular cavity
- muscles & nerve fibers
+/- third body cavity
(= coelom)
Acoelomata
Pseudocoelomata
- no third body cavity
Coelomata
- animals with
a true coelom
- pseudo- coelom
Platyhelminthes
(Flatworms)
Nematoda
- 10,000
- pharynx, no anus
- incomplete digestive
- nerve cord
- no vascular system
(Roundworms
- > 100,000 species
- mouth & anus
- complete digestive system
- no vascular
- hydrostatic skeleton
- nerve cords &
Graphic©E.Schmid/2000
red
=
Mollusca
Annelida
Arthropoda
Chordata
(see Part II)
animal phylum
4
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
The typical animal life cycle and embryonic development

most of our knowledge about the early stages of the animal life cycle and animal
Lyytteecchhiinnuuss
development, we owe the classical studies with sea urchins (L
vvaarriieeggaattuuss)
 historically, sea urchins were a key model system in answering many
questions regarding the mechanisms of fertilization and egg activation, cleavage,
gastrulation and early development of the embryo

animals spend their entire life cycle as diploid cells, with the exception of singlecelled, haploid gametes; therefore, animals are diploid biological organisms;
- all cells of the animal, with the exception of the gametes, have a double
chromosome set within the nucleus of their cells
- this is very different to plants, e.g. mosses and ferns, which have multi-cellular,
haploid structures (= gametophyte) which produces haploid gametes
1. the female/male adult animals make haploid cells, i.e. eegggg aanndd ssppeerrm
m, by
meiosis in the so-called gonads
 the gonades are called testis in males and ovary in females
2. one egg (= ooooccyyttee) and one ssppeerrm
m fuse in a process called fertilization to form
a ddiippllooiidd zzyyggoottee (2n)
 the zygote starts to divide by mitosis and goes through a
series of characteristic morphological stages
3. the zygote then undergoes mitotic divisions, which first forms a berry-like cell
complex called Morula and later leads to a stage of development called the
Blastula
 the blastocyst (blastula structure) consists of a single cell layer
around a fluid-filled cavity, called blastocoel
Early embryonic development of a typical animal
1. Early sea urchin (L. variegatus) Blastula
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SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
2. L. variegatus Blastula before onset of gastrulation
(Electronmicroscopic image)
4. the Blastula starts to fold inwards to form the so-called Gastrula
 the gastrula, which consists of an inner (= endoderm) and outer cell layer
(ectoderm), forms by infolding of the blastocyst in a blastopore
3. L. variegatus early and late Gastrula
(both viewed from the oral side)
E
Eaarrllyy ggaassttrruullaa
LLaattee ggaassttrruullaa
5. the Gastrula develops further and the still vastly enigmatic biological process,
called pattern formation, begins to shape the animal embryo with an opening
(the later mouth or anus) at one end
 this process creates outer and inner cell layers
 the outer cell layer, called ectoderm, develops into the so-called
epidermis, which builds the skin and the animals nervous system
 the inner cell layer (= endoderm) forms the animal’s digestive tract
 in most animals a third, so-called mesoderm, forms later, which
develops into most of the inner organs (e.g. liver, heart, lungs, etc.)
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SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Embryonic development & Environment
Embryonic pattern formation in animals is an enormously sensitive, “fragile” biological
process and can be negatively influenced (= inhibited) by drugs, medications (e.g.
Thalidomide in human embryos) and environmental toxins, e.g. heavy metals such as
cadmium or nickel (see Image of the sea urchin below)
P
Paatttteerrnn ffoorrm
maattiioonn aanndd eem
mbbrryyoonniicc ddeevveellooppm
meenntt iinn tthhee sseeaa uurrcchhiinn (( LL.. vvaarriieeggaatteess))
(both pictures show the bilateral or radial skeletal elements = spikules)
N
Noorrm
maall ddeevveellooppm
meenntt
IInn tthhee pprreesseennccee ooff N
Niicckkeell ((N
Nii))
 disruption of the normal pattern
formation of the primary mesenchyme
cells in the presence of the heavy metal
6. most animals develop:
a.)
b.)
directly into the adult organism
others develop into one or more so-called larval stages (e.g. seastar,
most insects)
7. in the latter case, the larvae undergoes a major change in body form and shape
in a process called metamorphosis
TTaaxxoonnoom
myy

in the past 300 years, scientists grouped the huge diversity of animals, according to
distinct evolutionary and adaptive traits, into so-called taxa; the scientific process of
grouping is called taxonomy

taxonomists established several methods of classification to build a taxonomic
system of the animal kingdom

the taxonomic system recognizes the generally accepted grouping of animals in socalled phyla, which are arranged in so-called phylogenetic trees,
7
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
1. Traditional classification:
- this method of systematics stresses both common ancestry (monophylesis) and
he degree of divergence among groups
- e.g. birds have feathers, reptiles have scales, and mammals have hair
- it goes back to the Swedish naturalist C
Caarrll LLiinnnnee’’, who attempted first to
classify all known species of his time (1753)
 however, evidences of past life forms (= fossil records) are not included in
this method of classification
 Linne’ established a hierarchical classification, which is based on the premise
that the species is the smallest unit, and that each species (or taxon) is
nested within a higher category
The Linnean classification of the animal kingdom
Domain:
E
EU
UK
KA
AR
RY
YO
OTTA
A
Kingdom:
A
Anniim
maalliiaa
Phylum:
Chordata
Class:
Mammalia
Order:
Primates
Family:
Hominidae
Genus:
Species:
Homo
sapiens L.
C
Cllaassssiiffiiccaattiioonn ttrraaiittss ooff tthhee kkiinnggddoom
m aanniim
maallss
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SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
2. Cladistic classification:
 this type of systematics groups organisms based on shared derived
characters, not the overall similarity of potential group members
 e.g. the presence of an amniotic egg is used to unite a group sharing common
ancestry
 this method was developed by W
Wiillllii H
Heennnniigg, who attempted to develop a
more objective method of classifying organisms
3. Phenetic classification
 species are clustered together based on the number of their similarities (or
differences, depending on the numerical coefficient employed)
 traits are measured and converted into integers or numerical data, which are
then mathematically processed using an algorithm that generates a similarity
or distance as the case
4. Genetic classification
 today more and more scientists use sensitive genetic and molecular
biological methods (= DNA sequencing, RNA sequencing, DNA
hybridization and sequence homology analysis) to examine phylogenetic
ancestry of biological organisms
 this powerful approach which compares different forms of life at the molecular
level (not only morphological level) is more and more supported by the use of
computer programs and algorithms ( Bioinformatics)

these morphologic and (nowadays) genetic studies helped to establish the modern
phylogenetic tree for the animal kingdom

today the animal kingdom is grouped into more than 35 phyla, which comprise
approx. 1 million species; nine of these phyla generally comprise the bulk of the
kingdom, which are: Porifera, Cnidaria, Platyhelminthes, Nematoda, Mollusca,
Annelida, Arthropoda, Echinodermata and Chordata
The phylogenetic tree of Animalia
A
AN
NIIM
MA
ALLIIA
A
IIN
NV
VE
ER
RTTE
EB
BR
RA
ATTA
A
1.
2.
3.
4.
5.
6.
PORIFERA (sponges)
CNIDARIA (e.g. medusa)
BILATERIA
(flatworms, roundworms)
MOLLUSKA (e.g. snails)
ANNELIDA
(e.g. earthworms)
ARTHROPODA
(e.g. insects)
V
VE
ER
RTTE
EB
BR
RA
ATTA
A
7. PISCES (fishes)
8. AMPHIBIA (e.g. frog)
9. REPTILIA
(e.g. snakes)
10. AVES (birds)
11. MAMMALIA
(e.g. mouse, man)
9
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Summary of important body (= morphological) features nine animal phyla
11.. P
PO
OR
RIIFFE
ER
RA
A ((S
SP
PO
ON
NG
GE
ES
S))







about 5000 species are known, most of which are marine
among them are the most simple animals
sponges are believed to have evolved from a colonial protozoan
there are no true tissues in sponges and only merely specialized cell layers
(therefore: “false animals”)
they don’t have a digestive tract and digest intracellularly (= inside the cell body)
lack a nervous system and muscles
most sponges feed from bacteria by drawing water into the body through a network
of pores (hence the name porifera = pore-bearer) and passing it out through the
large opening (osculum) at one end of the body
S
Sttaaggeess ooff tthhee lliiffee ccyyccllee ooff aa ssppoonnggee
1. a mature sponge produces hhaappllooiidd eeggggss aanndd ssppeerrm
m that are released into the
central cavity
2. after fertilization, the ddiippllooiidd zzyyggoottee develops into a ciliated larva without a Gastrula
stage (no Gastrula appears)
10
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
3. the larval stage is mobile and able to move around, while the adult (= sponge) is
stationary the lack a of development

sponges are able to reproduce asexually by so-called fragmentation
 a released fragment develops into a new sponge

2 types of sponges are known
11.. V
Vaassee--sshhaappeedd oorr ccyylliinnddrriiccaall ssppoonnggeess
 have a radial symmetry = the body parts are oriented around a
central axis
 e.g. S
Sccyypphhaa
 consists of 3 cell types
1. outside and pore-forming cells
 have protective function and regulate the incoming water flow
2. motile amoebocytes with skeletal components
 have delivery and carrier function
 carry the nutrients and metabolites to other cells
3. choanocytes or collar cells
 are flagellated cells which engulf trapped bacteria by a process
called phagocytosis
22.. C
Chhooaannooffllaaggeellllaatteess
 is a cluster of flagellated collar cells attached to a stalk, which has
soil contact
 ancestors lived already in the Precambrian seas
 it is assumed that sponges and all animals arose from a
choanoflagellate ancestor
11
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
IIm
maaggee ooff aa ttyyppiiccaall ssppoonnggee aanndd cchhooaannooffllaaggeellllaattee
22.. C
CN
NIID
DA
AR
RIIA
A






the phylum Cnidaria contains 10,000 species, e.g. Hydras, sea anemones, jellies
(‘jelly fish’) and corals, which are characterized by adult bodies having radial
symmetry
Cnidarians are aquatic, mostly all marine
they have true tissues and are therefore also called tissue animals; but they lack
the mesoderm, and only show ectoderm and endoderm tissue layers
Cnidaria are carnivores and capture small animals and protists with the help of
stinging cells called cnidocytes
 these unique and specialized cells each contain a nematocyst, which
is a fluid-filled capsule with a long, spirally coiled hollow thread
 on contact with a prey, this barbed thread, together with a toxin is
ejected to trap and kill the victim
the prey is put in their mouths which leads into a digestive compartment, the socalled gastrovascular cavity
 since they do not have an anus, the undigested food and
other nutritional waste exits through the mouth again
Cnidarians have both, muscle fibers and nerve fibers
 these animals are capable of directional movement and of
transmission of messages in more than one direction
12
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Body shapes of a typical polyp and medusa (Phylum: Cnidaria)
Stages of the life cycle of a typical Cnidarian
The life cycle of a typical Cnidarian

The typical Cnidarian life cycle involves both sexual and asexual reproduction

Cnidarians show "alternation of generations" between the sessile ppoollyypp pphhaassee
and the mobile m
meedduussaa pphhaassee
 but unlike plants, both phases are diploid

after fertilization of an egg cell by free-swimming sperm, a bilaterally symmetrical
larva known as a planula, develops from the zygote; the larva development shows
a clear Gastrula stage
13
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.

the planula settles in an appropriate location and grows into an adult polyp
 a polyp is a mostly stationary, cylindrical body with tentacles on top
 it has so-called stinger cells (= Cnidocytes) on the surface of the
polyps tentacles

the polyp reproduces asexually to form a stage called medusa
 a medusa is a free-swimming, umbrella-shaped body with fringes of
tentacles
 have a soft, glassy-transparent body
 some of the medusas show so-called bioluminescence due to the
activity of a special protein called aquorin (e.g. Aquoria species)
 many medusa produce and release biologically highly active
compounds (toxins), which are able to paralyze or kill their prey
 some of these toxins are strong irritants to humans and can cause
severe rashes and burns

each medusa develops gonads which start to form gametes (= egg and sperm) by
meiosis

some species, e.g. the sea nettle, exist only as a medusa while others, such as
Hydra or the sea anemones, exits only as polyps
33.. B
BIILLA
ATTE
ER
RIIA
A

an important "fork in the road" of evolution, occurred with the divergence of
bilaterally symmetric animals from the irregularly-shaped Porifera (=sponges) and
the radially symmetric Cnidarians

Bilaterally symmetric animals tend to swim or move in a head-first direction; they are
marked by a distinct posterior and anterior end (= head and tail), as well as by
dorsal and ventral surfaces
3.1.
Flatworms (= Phylum: PLATYHELMINTHES)

the Phylum Platyhelminthes contains about 13,000 species of flatworms

they have a so-called bilateral symmetry of their body
 the animals body has two mirror-image left and right sides
 have an anterior head region and a posterior end part of the body

they have three tissue layers: ectoderm, mesoderm and endoderm
 the mesoderm layer gives rise to muscles and reproductive organs
 The presence of three muscle layers facilitates varied movement
 gland cells secrete a mucous material upon which the animal slides
or glides
14
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.

their body plan is acoelomate; they have only one interior space (= the digestive
tract) and no third body cavity (see roundworms!)

their body shape is sac-like with a single opening, called pharynx

they capture food by wrapping itself around prey and entangling it in slime

flatworms have (like the Cnidarians) an incomplete digestive tract (= no anus!); the
gastrovascular cavity is highly branched
 it distributes nutrients throughout the body and is the site of
extracellular digestion

flatworms have two light-sensitive eyespots that have pigmentation ( primitive
form of bright/dark vision for sense of orientation)
they have muscles, a nerve cord, and digestive organs, but have no respiratory or
circulatory system
 gas exchange occurs by diffusion through the skin


the length of different species varies from 1mm to (in the case of tape worms) up to
20 meter (!!)
TThhee ttyyppiiccaall lliiffee ccyyccllee ooff ffllaattw
woorrm
mss

flatworms, such as Planaria, can reproduce sexually and asexually

in asexual reproduction, the body constricts beneath the pharynx and each half will
grow into a whole animal by a biological process called regeneration

since Planaria are so-called hermaphroditic animals, i.e. they possess both male
and female sex organs, it comes to cross-fertilization during sexual reproduction

after fertilization, the zygotes (= fertilized eggs) are enclosed in a cocoon and hatch
in two to three weeks
15
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Typical anatomy of a flatworm (Phyla: Platyhelminthes)

3 types of flatworms are known
11.. FFrreeee lliivviinngg ffllaattw
woorrm
mss ((C
Cllaassss:: TTuurrbbeellllaarriiaa))





the class Turbellaria includes the 5-10 mm long freshwater planaria, such as
D
Duuggeessiiaa
have a nervous system with a simple brain, nervous cords and eyespots
have tissue clusters and a single mouth opening (= pharynx)
the mouth leads into a highly branched digestive tract
live under rocks in freshwater ponds and streams, where they crawl on ventral cilia
in search for food
22.. FFlluukkeess ((C
Cllaassss:: TTrreem
maattooddaa))







the Class TTrreem
maattooddaa includes flukes
all flukes are parasitic and are named after the organs they inhabit, e.g. blood
flukes, liver flukes or lung flukes
the fluke bodies tend to be oval and elongate
flukes lack a definite head, but have an oral sucker surrounded by sensory papillae
flukes have reduced digestive, nervous, and excretory systems, but the reproductive
systems are well developed
they are usually hermaphrodites
a prominent example of a fluke is S
Scchhiissttoossoom
maa;
 it’s larvae infect and invade humans, where they attach to the blood
vessels near the intestines, after uptake of infectious water
 there they reproduce sexually and the fertilized eggs pass out via the
feces
 the hatched eggs infect a water snail and they asexually reproduce in
this host organism into an infectious larvae again;
 Schistosoma causes a persistent disease in humans, called
16
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Schistosomiasis, which is accompanied by anemia and abdominal
pains
33.. TTaappeew
woorrm
mss ((C
Cllaassss:: C
Ceessttooddaa))






the Class C
Ceessttooddaa consists of the tapeworms
tapeworms are like flukes also parasitic organisms
they inhabit the digestive tracts of vertebrate animals, reptiles, birds and mammals,
where they directly absorb the already digested food of their hosts; therefore they do
not have an own digestive tract
they have very long, ribbon-like bodies with repeating segments
the tapeworm’s head or also called the scolex has typical hooks and suckers that
allow the organism to attach to the host's intestinal wall
behind the head is a short neck and then a long string of so-called proglottids
 each proglottid segment contains a full set of both male and female
sex organs and very little other structure

following fertilization, ripe eggs appear in the last, posterior proglottid, which breaks
off and leaves the host via it’s feces

when the released tapeworm eggs are ingested by pigs or cattle, the larvae burrow
through the intestinal wall and travel by bloodstream to the muscles where it
becomes encysted
 a cyst is a hard-walled structure sheltering a larval worm

if humans eat under-cooked meat of infected pigs or cattle they become infected, too
 e.g. TTaaeenniiaarryynncchhuuss; can reach up to 20 meters (!!) in the human
intestine if not medically treated
3.2.
Roundworms (= Phylum: NEMATODA)

the phylum Nematoda comprises several hundred thousand species of roundworms

most are free-living, although some parasitic species are known
 pinworms are thought to infect 30% of all US children

its numerous species inhabit virtually every place on Earth
 some live on rotten organic matter and are organic decomposers
 some live in soil or on ocean floors

roundworms have a cylindrical body shape with finely tapered tail and a more
blunted head region

developed a skin = a layer of non-living cells which have protective function
17
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.

have a complete digestive tract with mouth and anus
 food travels one way through the gastrointestinal system
 anterior part breaks down (= digests) food with the help of digestive
enzymes
 the posterior part absorbs the food components and nutrients

nematodes lack a circulatory system, but do have a well developed digestive
system

nematoda is the first phylus of animals which developed a third body compartment,
called body cavity; adult nematodes have a typical “tube-within-a-tube” body
structure, which is also called a pseudo-coelom
 a pseudo-coelom is a closed, fluid-filled space that acts as a
hydrostatic skeleton, aids in circulation and dispersal of nutrients
Coelom-less animals (Acoelomates)
(e.g. flatworms, flukes)
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SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Development of a body cavity (= pseudo-coelom) in nematods
 the body cavity does not develop from splitting of the mesoderm

with the exception of C
Caaeennoorrhhaabbddiittiiss eelleeggaannss, little is known about the life cycles of
roundworms and their metabolism

some roundworms are serious agricultural pests and attack the roots of plants

some live as parasites in animals or the human body; humans are host to about 50
species of roundworms
 e.g. hhooookkw
woorrm
mss; attach to the intestinal wall and suck blood
E
Exxaam
mpplleess ooff rroouunnddw
woorrm
mss::
1. C
Caaeennoorrhhaabbddiittiiss eelleeggaannss
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


C. elegans is a small roundworm and an important so-called model organism in
Biology
it consists of only about 1000 cells
 for comparison: the human body is made of 60 trillion cells !!!)
C. elegans has only 1000 genes in its genome; it therefore serves an important
organism in biological research, where it is used as a model to study eukaryotic
gene expression, aging and the role of genes in animal development and heredity
especially aging research with C. elegans lead to the discovery of
several “aging genes” which are involved in the aging process in this
organism
it has been extensively studied as part of the human genome project, and the DNA
of it’s complete genome has been successfully sequenced
19
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
22.. TTrriicchhiinneellllaa ssppiirraalliiss


T. spiralis migrates into muscle tissues where it reproduces
this roundworm causes trichinosis in affected mammals and humans; causes
nausea and in, case the worm enters the heart tissue, sometimes leads to death
 worms are acquired by people who eat undercooked pork meat
33.. A
Assccaarriiss






Ascaris is a parasitic roundworm, which thrives in warmer climate zones
these worms are un-segmented and have a smooth outside wall
after mating and fertilization the eggs mature in the soil; when these eggs are
swallowed, the ingested larvae burrow through the intestinal wall and move to the
liver, heart and/or lungs
within the lungs, the larvae molt and, after 10 days, migrate up the windpipe to the
throat where they are swallowed
in the intestine, the mature worms mate and the female deposits the fertilized eggs
that are lost with the feces; this feces must reach the mouth of the next host to
complete the life cycle
therefore, proper sanitation is advised to prevent Ascaris infections
Anatomy of a typical roundworm (Phylum: Nematoda)
20
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Trichinella sp. larvae in muscle tissue
TThhee eevvoolluuttiioonn ((““iinnvveennttiioonn””)) ooff aa bbooddyy ccaavviittyy bbrroouugghhtt aanniim
maallss m
maannyy aaddvvaannttaaggeess
1. increases the animals flexibility and motility
2. it suspends the organs from the surrounding mesentary tissue
3. the enclosed fluids in the body cavity cushion the internal organs and structures from
impact and prevent injury
4. it improves the circulation of nutrients and oxygen through the body and assists in
waste disposal
5. it enabled the appearance of larger animals

during the Cambrian-Ordovician era of Earth history, a huge diversity of animals with
a series of new “invention” appeared on the scene of life; due to the sudden
appearance of almost all major animal phyla during that ear, scientists tend to speak
of the “Cambrian explosion” in animal evolution

during that time animals evolved which had for the first time “real” internal body
cavities, called coeloms and external skeletons

today, all highly developed animals are coelomates; they have real body cavities
formed by the embryonic mesoderm layer
 we humans are coelomates, too; we have an abdominal (digestive
21
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
organs, some of the excretory and reproductive organs) and a
thoracic cavity (heart and lungs).
44.. M
Moolllluusskkss ((== P
Phhyylluum
m:: M
MO
OLLLLU
US
SC
CA
A))



the phylum Mollusca contains over 100,000 species with a variety of body forms and
lifestyles, e.g. snails, clams
most have a soft body protected by a hard, calcified shell
mollusca have two typical body features
1. a foot
 a muscular tissue which extends from the main body
 serves for locomotion or penetration
2. a mantle
 is an outgrowth of the body surface
 in clams and snails the mantle produces the shell
 functions in respiration, waste disposal and sensory
reception
 the so-called mantle cavity harbors gills or lungs; these
organs enable the uptake and exchange of gases, i.e.
oxygen, from water or air, respectively

most mollusks have a so-called radula in their mouth region
 it is a rasping organ with which help mollusks scrape and
chop their plant food (e.g. algae, plant leaves)

have a real coelom, which is reduced and limited to the region around the heart
 it consists of three cavities which enclose the heart, kidney and the
reproductive organs
mollusks developed already a primitive circulatory system which branches out
from the heart into the body parts
 the heart of this so-called “open circulatory system” pumps
hemolymph through vessels into a hemocoel
 the blood diffuses back to the heart and is pumped out to the body
again
they have a developed nervous system which consists of several so-called ganglia
connected by nerve cords


22
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Anatomy of a typical aquatic gastropod (Phylum: Mollusca)
A
Annaattoom
myy ooff aa ttyyppiiccaall bbiivvaallvvee ((P
Phhyylluum
m:: M
Moolllluussccaa))

3 different classes of mollusks are known
11.. G
Gaassttrrooppooddaa



builds the largest group of mollusks with over 75,000 species
 the only group which comprises land inhabitants
 e.g. the vineyard snail H
Heelliixx ppoom
maattiiaa, which has lungs instead of gills
and breathes air; it has primitive eyes which sit on a pair of
antenna-like, retractable body extensions, has one helical shaped shell made of
calcified proteins
the class Gastropoda includes the snails, terrestrial slugs, whelks, conchs,
periwinkles, sea hares, and sea slugs
most gastropods are marine inhabitants
23
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.


most gastropods have a well developed head with eyes and tentacles projecting
from a coiled shell that protects the visceral mass
in aquatic gastropods the mantle cavity under the shell harbors the gills; in
terrestrial gastropods, the mantle is richly supplied with blood vessels and functions
as a lung when air is moved in and out through respiratory pores
LLiiffee ccyyccllee ssttaaggeess ooff ggaassttrrooppooddss


aquatic but not terrestrial gastropods have a swimming larval stage
terrestrial gastropods are hermaphroditic animals
1. during mating each individual inserts a penis into the vagina for the other to
provide sperm for future fertilization of eggs
2. the fertilized eggs are deposited in the soil and the embryo development
proceeds without formation of a larval stage

Hermaphroditism assures in slow-moving animals that any two animals that meet
can reproduce
22.. B
Biivvaallvveess




this class of mollusks consists of the clams, oysters, mussels, and scallops
 most are marine species which are sedentary and live in mud or sand
on the ocean floor
"Bivalves" are two-part shells that are linked by a hinge-like so-called ligament and
usually kept closed by powerful muscles
 the muscular foot is used for digging and anchoring
the presence of shells in this group has yielded an impressive fossil record
the bivalves have no head, no radula, and little cephalization; many have multiple,
eye-like sensory organs which are able to detect movement
33.. C
Ceepphhaallooppooddaa

the class Cephalopoda (literally "head-footed") includes squids, cuttlefish,
octopuses, and nautiluses (and extinct relatives, the ggoonniiaattiitteess, aam
mm
moonnooiiddss, and
aam
mm
moonniitteess)
 amongst them are successful marine predators
 Squids and octopuses are fast animals thanks to a form of
“biological jet propulsion”
 they can squeeze water from their mantle cavity out through a funnel,
which propels them
 surrounding their head are tentacles with suckers that can grasp prey
and deliver it to a powerful beak/mouth

cephalopods developed a large, complex brain and highly sophisticated sensory
organs

they have eyes (with lenses and retina), which are considered to be the most
sensitive in the animal kingdom
24
SAN DIEGO MESA COLLEGE
SCHOOL OF NATRUAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
 the eye of the giant squid is the largest known sensory organ on our
planet and the biggest examples measured 30 cm!!

octopuses show learning behavour in laboratory experiments
25