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Chap 33: Invertebrates
Parazoa
Introduction
•
Choanoflagellates are the ancestors of the animal kingdom
•
Sponges are the closest animal to these ancestors
Phylum Porifera: Sponges
•
Basic Characteristics
•
Sessile
•
No nerves or muscles but can respond to events in the environment.
•
No true tissues
•
Have porous bodies through which water is drawn in
•
Spongocel: the central cavity
Figure 33.1 Review of animal phylogeny
Figure 33.3 Anatomy of a sponge
Filter Feeders
Sponges
•
How do we know that sponges are related to the early
choanoflagellates?
• The cells of the choanoflagellates and the choanocytes are similar
in terms of molecular makeup.
•
Presence of spicules: these are sharp fibers made of calcium carbonate
• Some of the fibers are not so rigid and made of collagen protein
and this is what the bath sponges are made of.
•
Sponge Sex
• They are hermaphroditic so they can produce both sperm and egg
cells. Eggs reside in a gelatinous layer, the mesohyl, while the sperm
cells are released out the osculum.
•
Cross fertilization can occur
• Fertilization occurs in the mesohyl and the zygotes develop
flagellum and swim away from the parent.
Sponges
• Asexual reproduction is possible by fragments of a sponge
breaking off and developing into a new organism
•
Regeneration is possible.
Radiata
Introduction
•
Possess true tissues
•
Radially symmetrical
•
Embryos possess ectoderm and endoderm (diploblastic)
Phylum Cnidaria: hydras, jellies, sea anemones and corals
•
Basic Characteristics
• Possess a gastrovascular cavity
•
Single opening for mouth and anus
•
Two body forms (plans)
•
Polyps: adhere to a substratum and extend tentacles
• Medusa: “mouth-down” version; mobile by drifting and
contracting of the bells.
Figure 33.4 Polyp and medusa forms of cnidarians
Figure 33.4bx Jelly medusa
Figure 33.6 Cnidarians: Hydrozoans (top left), jelly (top right), sea anemone (bottom
left), coral polyps (bottom right)
Figure 33.5 A cnidocyte of a hydra
Carnivorous
Cnidarians
•
Carnivorous
• Cnidocytes: a specialized cell that causes the projects of a
stinging capsule called a nematocyst.
•
Class Hydrozoa
•
Hydras
•
Can reproduce by budding (asexual) with conditions are good
•
Can reproduce sexually forming dormant zygotes if
conditions are harsh.
Figure 33.7 The life cycle of the hydrozoan Obelia (Layer 3)
•
Class Scyphozoa
•
•
Jellies
Class Anthozoa
•
Sea anemones and corals
•
Occur only as polyps, attached to a substrate.
Phylum Ctenophora: Comb jellies
•
100 species of comb jellies
•
The descriptor, “comb” comes from the 8 rows of fused cilia.
Figure 33.8x2 Ctenophore
Figure 33.8x1 Sea gooseberry, Pleurobrachia pileus
Combs
rows of cilia are used for locomotion
Comb jellies and cnidarians are in different
phyla. Both are radiate and diploblastic.
Tentacles: capture food with their adhesive
structures (colloblasts). These colloblasts when
stimulated by touch will release a sticky thread.
Protostomia: Lophotrochozoa
Introduction
•
Protostomes represent Bilateral Symmetry (see Fig 33.1, pg 647)
•
Protostomes are the planaria, flatworms, earthworms, mollusks,
arthropods such as insects, crayfish, spiders.
Phylum Platyhelminthes: Flatworms
•
Introduction
•
many parasitic species (tapeworms)
•
marine and freshwater as well as terrestrial flatworms
•
Triploblastic: possess endo- ecto- and mesoderm
•
being triploblastic allows them greater complexity in organ
development.
• Acoelomates, that is there is no space between their outer body
wall and digestive digestive tract.
•
•
Possess a gastrovascular cavity with one opening (like hydra)
Class Tubellaria
•
Planarians
•
Digestion
•Carnivorous
•Gastrovascular cavity
•
Respiration and Circulation
•One-cell layer thick for diffusion of gases
•Food is distributed by the branching of the gv cavity.
Figure 33.9x A flatworm
•
Movement
•Beating cilia on a secreted mucus layer
•
Nervous System
•More sophisticated then cnidarians
•Can learn to modify responses to the environment
•Possess eyespots to detect light
•Lateral flaps for hearing
•
Excretion
•Gases diffuse out
•Flame cells circulate water over ducts that carry water and
salt to the exterior.
•
Reproduction
•They can regenerate (asexual) by the parent simply splitting in
the middle and each half regenerates
•Sexual reproduction: cross fertilize
•Hermaphroditic but not fertilize themselves
Figure 33.10 Anatomy of a planarian
•
Classes Monogenea and Trematoda
•
Flukes (such as Schistosoma or blood flukes)
•
Digestion
•Parasitic and possess suckers
•
Reproduction
•Their internal spaces are filled with reproductive organs because
that is all they need to worry about being parasites.
•
Class Cestoidea
•
Tapeworms
•
•
Digestion
•Parasitic with the head or scolex possessing suckers and
hooks that lock onto your intestine.
Reproduction
•Body parts are units of proglottids which are sacs of sex organs
containing eggs.
Figure 33.11 The life history of a blood fluke, Schistosoma mansoni
•
Reproduction (cont’d)
•Proglottids leave the person’s body with the feces. An
intermediate host such as pigs, cattle, pick up the eggs that
develop into larvae and are embedded in their muscle tissue. We
eat the muscle tissue, larvae get into our intestine and mature.
Figure 33.12 Anatomy of a tapeworm
Phylum Rotifera (Rotifers)
•
Basic Characteristics
•
Pseudocoelomates:
•
Possess a complete digestive tract with a mouth and anus
that is, they have a body cavity but it is not
completely lined by mesoderm. The
acoelomates do not have a body cavity and
the coelomates have a body cavity
completely lined by mesoderm.
•
Water is drawn in through the mouth by cilia
•
A pharynx bears jaws for grinding food (microorganisms)
• Fluid the pseudocoelom serves as a skeleton as well as medium in
which nutrients and wastes are transported.
•
The pseudocoelom is also the circulatory system
• Undergoes parthenogenesis, the production of females from
unfertilized eggs.
• Some species produce two types of eggs: one undergoes
parthenogenesis and produces females, the other develops into
males by parthenogenesis. These males survive just long enough
to produce sperm. Fertilization occurs, zygotes form that
withstand drought conditions and then develop into a female.
Figure 33.13 A rotifer
Phylum Lophophorate
•
Identifying Characteristic
• Lophophore or a horseshoe-shaped piece of body wall that bears
ciliated tentacles that surround the mouth.
•
•
•
Cilia draws water in, traps food
Have true coeloms lined by mesoderm
Brachiopods
• possess a hinged shell with its two halves being dorsal and ventral
and not like clams which have lateral shells.
Figure 33.14 Lophophorates: Bryozoan (left), brachiopod (right)
Lophophore
Phylum Nemertea or proboscis worms
•
•
Basic Characteristics
•
Body shaped is ribbon like
•
Excretory System: gas diffusion through body wall
•
Possess eyespots like flatworms.
Unique Features
•
Complete digestive tract
• Closed Circulatory System: blood within vessels; no heart but
blood is moved by muscle contraction on the vessels thus squeezing
the blood throughout the body.
Phylum Mollusca
•
Examples: snails, slugs, oysters, clams, octopuses, squids
•
Where they live
•
•
mostly marine, terrestrial
Skeleton
•
external made of calcium carbonate
• octopuses and squids have internals skeleton or they have lost their
skeleton completely
•
Body Plan
•
3 main parts
•
Foot: muscular; for movement
•
Visceral Mass: contains internal organs
•
Mantle: tissue that hangs over the internal organs and also
secretes the shell.
•Also produces a water filled chamber for gills, anus and
excretory pores for clams and other similar mollusks
•
Digestive System
•
Radula: scraps food from surfaces
•
Complete digestive system (see next slide)
Figure 33.16 Basic body plan of mollusks
•
Reproduction
• Separate sexes with ovaries and testes located in the visceral
mass.
•
Snails can be hermaphroditic
•
Trochophore: ciliated larval stage
Figure 33.17 A chiton
•
Class Polyplacophora
•
Chitons (not chitin)
•
have 8 dorsal plates
•
use radulas to obtain food from surfaces
Figure 33.18 The results of torsion in a gastropod
•
Class Gastropods
• Torsion: a characteristic feature where the contraction of a
muscle during embryonic development and uneven growth places the
anus and mantle cavity above the head. Advantage? To possibly
locate these structures more centrally over the body.
• One of few invertebrates to have successfully
populated land.
• Land snails have a
moist lining for gas
exchange. No gills unless
it is aquatic.
Figure 33.18x Garden snail
Figure 33.19 Gastropods: Nudibranchs (top left and top right), terrestrial snail
(bottom left), deer cowrie (bottom right)
Sea Slugs
•
Class Bivalvia
•
Examples: clams, oyster, mussels, scallops
•
Muscular System
•
•
•
Adductor muscle which closes the two shells
Movement
•
by a foot that gets extended out of the shell
•
can also be used to anchor the clam
• mostly sedentary
Respiration
•
has gills that water flows over
•
water is taken in through the incurrent siphon and out of the
mantle cavity through the excurrent siphon
Figure 33.21 Anatomy of a clam
•
•
Digestive System
•
water that is brought in through the incurrent siphon brings
in food particles that get trapped on mucus that is on the
gills.
•
cilia beat to food these food particles to the mouth
•
no radula for the scraping of food
Nervous System
•
Scallops possess eyes
Figure 33.20 A bivalve: Scallop
Eyes are between the
two halves.
•
Class Cephalopoda
•
Examples: octopuses, squids
•
Digestive System
•
•
Carnivorous: eat clams
•
Possess jaws
•
Inject poison to immobilize prey
•
Possess a mouth
Skeletal System
•
Nautiluses have an external skeleton; otherwise the shell is
greatly decreased or lost
•
Movement
•
•
Water is drawn into the mantle cavity and fired out the
excurrent siphon. The siphon can be pointed for directional
movement.
•
Most live on the ocean bottom
Circulatory System
•
•
Closed circulatory system
Nervous System
•
Well-developed
•
Brain is able to learn
•
Well-developed sense organs
Figure 33.22 Cephalopods: Squid (top left and bottom left), nautilus (top right),
octopus (bottom right)
What’s the big deal about the Phylum Annelida or segmented worms?
•
Presence of a coelom or body cavity
•
provides space for digestive organs
•
acts as a cushion to protect these internal organs
• separates the muscular outer body wall from the muscular
intestine
• provides space for fluid to support the body (a hydrostatic
skeleton)
•
Segmentation
• the body plan of animals is becoming localized to certain areas.
This theme is present in many other animals.
Phylum Annelida or the segmented worms like earthworms.
•
Habitat: soil, marine, freshwater.
•
Digestive System
•
Specialized into several areas or compartments:
•
pharynx
•
esophagus
•
crop
•
gizzard
•
intestine
• eats its way through soil, digest soil and waste is “deposited” as
castings.
• ecological role: aerates soil; improves texture
•
Circulatory System
•
Closed
•
Hemoglobin is the oxygen carrying pigment
• Dorsal blood vessel with 5 pairs of vessels serve as a pumping
mechanism to get blood into the ventral blood vessel and distributed
•
•
Blood is carried right to the skin for gas exchange
Excretory System
• Functioning unit is the metanephridia. Located in each segment of
the earthworm’s body
• Liquid and wastes are removed from the segments through a
funnel called a nephrostome that will carry the wastes to the outside
and excrete it through a small pore.
•
Nervous System
• Possesses a collection of nerve cells, ganglia, one ganglia on each
side of the pharynx.
• Nerves run through a nerve cord that runs to the end, the ventral
nerve cord
• Along the ventral nerve cord are collections of nerves into
ganglia from which nerves branch out laterally
•
Muscular System
• Move by inserting bristles or setae into soil and using two sets of
muscles, longitudinal and circular.
•
Reproductive System
•
Hermaphroditic but they do not fertilize themselves
•
Sperm is exchanged
• The clitellum secretes a mucous cocoon that slides dorsally along
the earthworm, picks up the eggs and exchanged sperm and continues
towards the anterior and slides off. This cocoon contains the
developing embryos.
Figure 33.23x External anatomy of an earthworm
Figure 33.23 Anatomy of an earthworm
•
Class Oligochaeta
•
•
earthworms
Class Polychaeta
•
possess many setae for movement
• These setae are attached to a structure called a parapodia that
have lots of blood vessels, can exchange gases and function in
respiration.
•
Class Hirudinea
•
leeches
•
parasitic lifestyle in marine and freshwater
• contact with skin can be made with enzymes or with jaws. An
anesthetic is released so host does not feel the biting.
• Hirudin: anticoagulant so the blood keeps on flowing. Digestive
system here is not too complicated.
Figure 33.24 Annelids, the segmented worms: Polychaete (left), feather-duster worm
(middle), leech (right)
Protostomia: Ecdysozoa
Introduction
•
Roundworms, arthropods (crustaceans, spiders, insects) all molt or
lose their outer skeleton (exoskeleton) so they are in a “clade” called
ecdysozoa because they go through ecdysis or the loss of the
exoskeleton.
Phylum Nematoda (Caenorhabitis elegans or C. elegans)
•
Habitat
• moist soil or in marine or freshwater, moist parts of plants and in
the body fluids and tissues of animals.
•
Skeleton
•
has an external cuticle (exoskeleton) that it molts
•
new one is secreted.
•
Digestive System
•
•
•
•
similar to annelids, a complete digestive tract.
Circulatory System
•
No circulatory system
•
Nutrients are transported through the body cavity’s fluid
Reproductive System
•
sexual reproduction
•
internal fertilization
Ecological Importance
•
decomposition of matter; recycling of nutrients
•
Human Impact
• the roundworm, Trichinella spiralis, causes trichinosis which you get
from eating undercooked pork. The cyst of the roundworm is in the
muscle tissue you eat, finds its way to the intestine and burrows into the
intestine to mature. The offspring can infect other body tissues (heart
muscle) causing death.
Figure 33.25ax Nematode, C. elegans
Figure 33.25a Free-living nematode
Mouth
Figure 33.25b Parasite nematode, Trichinella spiralis
Distinguishing Features of the Arthropods
1.
Importance of the exoskeleton
a) allowed the move to land by some arthropods
b) protection in sea and on land
c)
prevented water loss on land; cuticle is impermeable to
water.
d) structural support since there is no water to “hold up” the
appendages.
2.
Segmentation
a) This represents the “segmentation” or “blocking of the
embryo into regions of development. Eyes go in the
“first segment” or the head region and then different
appendages are developed towards the posterior end.
b) Hox genes are responsible for determining what organ
goes in what segment.
2.
Segmentation
a) This represents the “segmentation” or “blocking of the
embryo into regions of development. Eyes go in the
“first segment” or the head region and then different
appendages are developed towards the posterior end.
b) Hox genes are responsible for determining what organ
goes in what segment.
c) As the Hox genes duplicated and mutated more
segmentation of the bodies occurred producing greater
diversity
Phylum Arthropoda
•
Habitat: diverse and everywhere are the crustaceans, insects, spiders.
•
Skeleton
•
hard chitinous exoskeleton or cuticle, lost and reformed
•
jointed appendages
• Body segments are specialized for attachment of appendages or
sensory reception, reproduction
•
Senses and Nervous System
•
eyes, smell, antennae for touch and smell
• Localization of nerves towards the head, known as cephalization,
is a distinguishing feature.
•
Circulatory System
•
Open
•
Fluid is called hemolymph, not blood
• Heart and short arteries but no extensive vessel development.
Hemolymph is pumped into the sinuses which surround the tissue.
Here the tissues pick up nutrients that they need and get rid of waste.
•
•
Hemolymph reenters heart through ports called ostia
Respiratory System
•
Aquatic arthropods have gills
• Terrestrial arthropods can take gases into through pores at the body
surface, through tracheal systems or ducts and branch to distribute
gases at the tissues.
•
Arthropod Phylogeny and Classification
•
4 main lineages of arthropods
•
(1) Trilobites
•
now extinct
• lots of segmentation which again is a major distinction as
animals became more sophisticated.
•
(2) Chelicerates (spiders, horseshoe crabs)
• have chelicerae which are the clawed appendages like in a
crayfish; possess a single lens eye
•
appendages are a bit more specialized than the trilobites
•
the chelicerae are the distinguishing appendage
• the horseshoe crabs have changed very little but has
existed for 100’s of millions of years
•
known as the “living fossil”
Figure 33.27 A trilobite fossil
•
Chelicerates (cont’d)
• possess book lungs as respiratory surfaces. These are
“pages”of respiratory surfaces for gas exchange between the
hemolymph and the air.
• Arachnids have 6 pairs of appendages, the chelicerae, the
pedipalps used for sensing or feeding and the 4 pairs of
walking legs.
•
Webs of silk are part of capturing food. Silk is a protein.
Figure 33.30b Spider anatomy
•
(3) Insects
•
possess mandibles or lower jaws for chewing
• possess antennae and compound eyes (many focusing
elements)
• Distinguishing feature to their success: flight
•
Important in pollination of plants (coevolution)
•
Complete digestive system
•
Open circulatory system with hemolymph and sinuses
• Excretory System: Malpighian tubules which extend
from the digestive tract, extract waste from the hemolymph.
• Respiratory System: Tracheal system of branched tubes
extending from the pores or spiracles in the chitinous
exoskeleton and carry oxygen right to the tissues.
•
Insects (cont’d)
• Nervous System: ventral nerve cord, ganglia throughout
the body. The two ventral nerve cords come together at the
head and from the brain. Antennae, eyes as sense organs.
•
Insects undergo metamorphosis
Incomplete metamorphosis: several moltings as the
body develops in proper portions to become an adult
with each molting.
Complete metamorphosis: larval stage looks
different from the adult (caterpillar) and
metamorphosis occurs during the pupa stage as the
caterpillar, in the cocoon becomes an adult.
• Reproduction is internal, sexual. Deposited sperm is stored
in a spermatheca.
•
(4) Crustaceans
• thrived in aquatic environments while the insects and
arachnids thrived on land.
• Multiple appendages: 2 pairs of antennae; 3 or more
mouthparts; walking legs
• Respiration: smaller ones can exchange gases across a
thin cuticle but larger crustaceans have feathery gills.
• Circulatory system: open; heart with hemolymph in
vessels and then into sinuses.
• Excretory system: some wastes (N) can diffuse across the
cuticle and salt wastes are regulated by salt glands.
•
Reproductive system: sexual reproduction
• Common species: isopods, copepods (food at the base of
the aquatic food chain, eaten by fish), decapods (lobsters)
Figure 33.35 Crustaceans: Lobster (top left), banded coral shrimp (bottom left),
barnacles (right)
Barnacles have shells of CaCO3
and use the appendages to filter
food from water.
Deuterostomia
Basic Characteristics
•
radial cleavage
•
mouth forms at the opposite end of the blastopore
•
body cavity or coelom develops from the archenteron
•
Examples of deuterostomes: sea stars, fish, amphibians, reptiles,
birds and mammals.
Phylum Echinodermata
•
Examples: sea stars, sea urchins, sea cucumbers.
•
Basic Characteristics
•
sessile or slow moving
• water vascular system: water is taken in by tube feet and passed
through channels under pressure that aid in movement, feeding and
gas exchange.
• Reproductive system: sexual where gametes are released into the
water.
• It is the larvae of the echinoderms that possess the bilateral
symmetry that relates them to the chordates.
Figure 33.38 Anatomy of a sea star
•
Class Asteroidea (sea stars)
• Digestive system: turn stomach inside out, out through its
mouth and in-between the shells of its prey. Digestive juices are
secreted / released into the shell of the clam.
• Regeneration of body parts and one genus can grow an
entire body from a piece of an arm.
•
Class Ophiuroidea (brittle stars)
•
•
Digestive system: suspension feeders, scavengers.
Class Echinoidea (sea urchins and sand dollars)
•
muscles move their spines around
•
possess tube feet but no arms like sea stars
Figure 33.37 Echinoderms: Sea star (top left), brittle star (top right), sea urchin
(bottom left), sea lily
(bottom right),
Phylum Chordata
•
Include invertebrates such as the sea squirts, lancelet and the
vertebrates (fish, amphibians, reptiles, birds, mammals)
•Once again, the grouping of echinoderms such as sea stars with
humans into the phylum chordata is due to their similarity in
embryonic development.