Outline for Invertebrates
Honors Version
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I. Overview of the phyla | National Biological Infrastructure - a wealth of info on species and
habitats | Encyclopedia of life
A. Phylum Porifera (sponges)
B. Phylum Cnidaria (corals and jellyfish)
C. Phylum Platyhelminthes (flatworms)
D. Phylum Nematoda (roundworms)
E. Phylum Annelida (segmented worms)
F. Phylum Arthropoda
1. Class Trilobita
2. Class Arachnida
3. Class Crustacea
4. Class Insecta
G. Phylum Mollusca
1. Class Gastropoda (snails)
2. Class Bivalvia (clams)
3. Class Cephalapoda (octopus, squids)
H. Phylum Echinodermata (sea urchins, starfish)
We will examine these groups from various angles:
1. anatomy/physiology
-digestion
-circulation
-skeleton, muscles (movement)
-excretory
-nervous system/brain
2. reproduction and development (how do they pass on offspring and disperse their offspring?)
3. ecology and behavior (how do they get energy? how do they defend themselves?)
Basic Overview:
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
What is an animal? p. 366
Animal body plans: p. 368, fig. 18.3
II. Phylum Porifera
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
more info
p. 3720
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more pictures
and info
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Photographs by
David Remsen,
copyright © 1995,
Marine Biological
Laboratory, Woods
Hole
A. anatomy - see figure 18.5
1. digestion - one opening (a sac)
water flows into pores and out the oral opening; flagella beat to
create water flow
2. skeleton - body supported by hard cells called spicules
3. no brain, circulatory system, or organs
B. Reproduction
1. sexual - hermaphroditic with ciliated larvae
2. asexual - budding/regeneration
C. Ecology
1. consumers - filter a great deal of water
2. preyed upon by some fish and by nudibranchs (sea slugs)
3. important part of shallow tropical ecosystems (coral reefs)
III. Phylum Cnidaria
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p. 371
links
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o
o
o
o
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more pictures
and information
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Aglantha digitale
(Hydrozoa), a
direct-developing
holoplanktonic
hydromedusa that
has no polyp. The
gonads are visible
through the
transparent bell.
Photograph
copyright © 1998,
Claudia E. Mills.
Coral reef - coral.org
Coral reef conservation
program
Coral discovery
program
Guided tour
Coral Reef information
system
A. Classification
1. class Hydrozoa (hydra)
2. class Scyphozoa (jellyfish)
3. class Anthozoa (corals and sea anemones)
B. anatomy/physiology
1. polyp stage
2. medusa stage

see illustrations of theses stages and of radial symmetry
3. digestion
a. a sac with one opening and two body layers
b. stinging cells disable prey (fig. 18.6D, p. 371)
4. radial symmetry (fig. 18.3A, p. 368)
5. no true brain; a simple "nerve net" allows communication
between cells
6. has sensory cells - eyespots for light and others that sense
chemicals/food
C. Reproduction/life cycle
1. sexual and asexual - note differing life cycles of corals and
jellyfish
2. during sexual reproduction, sperm must pass through the one
body opening
D. Ecology
1. corals are essential parts of reefs
2. symbiotic relationship with zoozanthelle, a dinoflagellate algae.
Pollution can cause the algae to die, a condition termed "coral
bleaching"
IV. Phylum Platyhelminthes
(flatworms) p. 372
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more pictures
and information

Micrograph of
Rugogaster
hyrdolagi Photo:
Shirley Dawson.
A. Classification
1. class Turbellaria – planaria
2. class Tremetoda – flukes
3. class Cestoda – tapeworms
B. anatomy/physiology – fig 18.7A, p. 372
1. digestion – possess a sac, a "dead end" gut, which may be
branched in order to reach all parts of the body
2. circulation – materials must reach cells by diffusion. That is why
they are flat.
3. excretory – cellular waste products leave through flame cells.
4. bilaterally symmetrical (see fig 18.3, p. 370)
5. nervous system shaped like a ladder; small brain
C. Reproduction
1. sexual reproduction is hermaphroditic in some
2. sexes are different sizes in some
3. asexual in the form of regeneration is possible with planaria
4. parasitic forms contain mostly reproductive organs and eggs
inside their bodies - they might be called "egg factories"
D. Ecology
1. planaria are free-living. They are carnivores and scavengers.
They are mostly marine, but a few live in freshwater ponds.
2. flukes - some are free-living and some parasitic.
· blood flukes such as Schistosoma infect 200 million people
annually
3. tapeworms
a. Have no mouth; have suckers for holding on to
tissue, and absorb nutrients through their skin (see
fig. 18.7B, p. 372)
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
examples of parasites
information on an new unidentified parasitic disease (more
here)
V. Phylum Nematoda
(roundworms)
A. anatomy/physiology
1. tube-within-a-tube digestive system (mouth and anus)
2. no skeleton; moves via hydrostatic pressure, pushing against
fluid in its body
3. C. elegans has been very extensively studied
· the fate of every cell during development is known
· first multicellular creature to have its entire genome sequenced
4. pseudocoelom – partial body cavity – p. 368, fig 18.3B
B. Reproduction
1. sexes separate
2. internal fertilization
C. Ecology
1. up to 800,000 different species (!)
2. live in water, muddy lake bottoms, soil
3. some are beneficial - act as decomposers and nitrogen fixers.
4. some are parasitic to humans, such as
a. Trichinella, which come from raw pork
b. hookworm
c. Ascaris
d. there are several which come from uncooked fish.
FDA recommends freezing fish at -31oF for 15
hours before eating raw.
e. river blindness
VI. Phylum Annelida

more pictures and
information

Photograph from Gray
Museum Slide Collection,
copyright © 1995,
Marine Biological
Laboratory, Woods Hole.
A. classification
1. class Hirudinea - leeches
2. class Oligochaeta - earthworms
B. anatomy/physiology (p. 376)
1. segmented - have the appearance of many rings strung together
(p. 376, fig. 18.10)
2. tube-within-a tube digestive system crosses all segments.
3. nephridia - cells that get rid of cellular wastes. A pair in each
segment
4. circulation - 5 hearts; two major blood vessels with branches in
each segment.
5. brain - small; nervous system with branches in each segment.
6. coelomate – p. 368, fig. 18.3D
B. Reproduction
1. sexual - hermaphoditic with cross fertilization
2. asexual - regeneration from cut worms is possible.
C. Ecology
1. earthworms (oligochaetes) are decomposers

Darwin estimated that 1 acre of British farmland has
approximately 50,000 earthworms, which produce about 18
tons of castings (waste) per year.
2. leeches - medicinal use as bloodsuckers; external parasites in the
wild (fig. 18.10D)
 medicinal leaches have an interesting symbiotic
relationship
VII. Phylum Mollusca (p. 380-381)
More pictures and
information
A. Features all mollusks have in common (fig. 18.9A, p. 374)
1. visceral mass or
mantle: this is the soft
body
2. external or internal
shell
3. muscular foot for
locomotion
4. some have a radula,
which is a rough tongue
for scraping food .
5. most have a ciliated
larva called a
trochophore
Photograph from
Gray Museum
Slide Collection,
copyright © 1995,
Marine Biological
Laboratory,
Woods Hole.
a chiton and a scallop
B. Class Gastropoda (= "stomach foot") - snails
1. tube-within-a-tube; position effected by torsion (anus is above
the head)
2. most have shells excreted by the soft body, expect for slugs
3. have a "foot" for locomotion
4. have a radula that scrapes food (most are herbivores; exceptions
include nudibranchs and oyster drills)
5. ecologically important in spite of their size.
C. class Bivalvia (pelecypoda) - mussels, scallops, and
clam dissection
clams. (fig. 18.9C and D, p. 374-375)
1. two-part, hinged shell.
2. filter feeders, with incurrent and excurrent siphon.
3. breathe with gills, like fish.
4. multiple eyes.
5. ecology - filter water, and are significant componants of both
fresh and saltwater ecosystems.


zebra mussels
take the web quest on zebra mussels
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D. Class Cephalopoda
(= "head-foot") (fig. 18.9F
and G, p. 375)
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
more pictures and
info
check out squid
anatomy
squid dissection
Interactive anatomy of a
cuttlefish
squid from the Gray
Museum Slide
Collection. Copyright ©
1995, Marine Biological
Laboratory, Woods
Hole.
1. tube-within-a-tube; beak
2. largest squid - 17m long, weighed 2 tons.

in search of giant squid -- cool site with animations!!
3. closed circulatory system - blood is always in vessels.
4. most complex brain/nervous system of any invertebrate.
5. locomotion - siphon
6. predators
7. ammonites - dominant, large cephalopods found as fossils.
Nautilus is the only living representative.
VIII. Phylum Arthropoda (p. 378-381)
A. general characteristics.
1. largest phylum (at
least 1 million
species; estimates of
up to 30 million)
2. hard exoskeleton,
which grows by
molting
3. distinct head and
abdomen regions.
4. open circulatory
systems – no
capillaries (fig. 23.1,
p. 468)
Blister beetle
(Eukaryotes,
Coleoptera) on a
composite flower
(Eukaryotes,
Asteraceae).
Photograph copyright
© 1995, David R.
Maddison.
insects are important
pollinators
5. jointed appendages.
B. class arachnida - spiders,
ticks, mites, and
scorpions.(fig. 18.11C, p.
379)
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More
pictures
and info
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SEM of
Allothyrus
sp. from
Queensland
(D.E.
Walter)
1. eight legs
2. pedipalps and chelicerae - appendages used to hold and tear
food.
3. separate sexes; elaborate courtship behavior.
4. respiration - book lungs
5. ecology: spiders are predators which build webs to attract prey;
mites and ticks are parasitic or at least require a host; scorpions are
predators.
6. horseshoe crab - related but
technically not arachnids (more ecological importance)
more horseshoe
crab web sites
C. class Crustacea (40,000 species) (fig. 18.11A, p. 378)


more about lobsters
Tidepools are home to many crustaceans and other invertebrates
1. 5 pairs of legs, with the front pair modified into claws.
2. two pair of antennae on the head. Also several mouthparts.
3. most are predators.
4. excretion through cells called green glands
5. very important ecologically
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crabs and lobsters are the top predators in some ecosystems
krill - base of marine food webs (plankton)
crayfish - many species are endangered, especially in the
SE United States.
More pictures
and info
D. class insecta - see p. 380-381
1. six legs
2. trachea for gas exchange - bring air to all cells
3. malpighean tubules - excratory organs for cellular waste
products.
4. most have wings, sometimes two pairs.
5. life cycle includes complete or imcomplete metamorphisis
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check out some cool insect facts!!
another great link - pictures and cool info
more links
explore the biology of social insects
Copyright © 1995, Joseph L.
Spencer.
Mayflies live as larvae in streams, where
they are sensitive to pollution. The adults live
for about a day -- long enough only to mate
6. ecology - perhaps the most important of any group, because they
are so diverse that they have filled nearly every ecological role. An
ecosystem without vertabrates could probably function quite well
as long as insects were present.
Perlesta decipiens
nymph, photograph by C.
Riley Nelson, copyright
1996.
Stonefly larvae, like mayflies, are sensitive to water
pollution. Their presence indicates a healthy stream.
Grumichella sp.
(Integripalpia:
Leptoceridae), Río
Montalban, Venezuela.
Illustration copyright ©
1997, James C. Hodges,
Jr.
Caddis fly larvae, which build themselves shelters, are
also sensitive to pollution
7. insect pests - how should they be controlled?
8. taxonomy - insect orders
a. Lepidoptera - butterflies.
b. hymenoptera - bees and
wasps
c. odonata - dragonflies
d. ephemeroptera - mayflies
e. coleptera - beetles (largest
order)
f. hemiptera - true bugs
g. diptera - flies and
mosquitoes
h. isoptera - termites
beetle
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IX. Phylum Echinodermata
(p. 382)


more pictures and info
overview of
echinoderms
starfish dissection
Ophiopholis aculeata, a
starfish. Photograph from
Gray Museum Slide
Collection, copyright ©
1995, Marine Biological
Laboratory, Woods Hole.
A. classification - several important classes
1. starfish (sea stars)
2. sea urchins
3. sea cucumbers
B. anatomy/physiology (fig. 18.13A, p. 382)
1. radially symmetrical as adults but bilaterally symmetrical as
larvae
2. spiny skin and internal skeleton
3. movement with tube feet - use water pressure
4. feeding - stomach comes out of the body to digest the prey
5. respiration and excretion - tube feet can collect oxygen and
dispose of cellular waste.
6. parts come in multiples of 5, even for those without arms
C. Reproduction
1. sexual with external fertilization; ciliated, free-swimming larva
2. asexual via regeneration
3. development similar to chordates
D. Ecology

important members of coral reef communities and tidal communities. Can
be predators of corals and bivalves
X. Chordates (p. 383)
A. This phylum includes vertebrates, but also a few "oddball" species with no
backbone.
B. have these features in common:
1. dorsal, hollow nerve chord
2. post-anal tail
3. notochord (supports nerve chord during development)
4. pharyngeal "gill slits"
C. examples
1. tunicates (sea squirts) (fig. 18.14A)
2. salps
3. lancelets (fig. 18.14B)
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