BIO 104 4/26/96
Chapter 29: Animal Diversity II, pp 544-569 in Raven &
Johnson
I. Phylum Cnidaria - jellyfish, Hydra, corals, anemones; aquatic --
mostly marine, some fresh water species
A. Exhibit radial symmetry
1.Definition: body parts arranged symmetrically around
central axis -- refer to Figure 29.8, p 548 in Raven &
Johnson
2.polyp and medusa forms - see Figure 29.6, p 547 in
Raven & Johnson
a. polyp - sessile, hydrozoans, anemones, & corals
have polyps as the predominant body form (refer to
Figure 29.5 (a), p 546 in Raven & Johnson)
b. medusa - free-swimming; dispersal stage for many
cnidarians (refer to Figure 29.5 (b), p 546 in
Raven & Johnson)
c. some cnidarians alternate between an a sexual
polyp and a sexual medusa
B. cells of cnidarians-tissue level of organization
1. diploblastic: organized into two tissue layers
a. epidermis derived from ectoderm
b. gastrodermis derived from endoderm
c. mesoglea in between ("jelly-like" substance
which give jellyfish their common name)
2. cnidocytes-specialized stinging cells which give the
phylum its name (refer to Figure 29.7, p 547 in Raven &
Johnson)
a. contain harpoon-like structures called
nematocysts
b. venom which paralyzes prey
c. some varieties are toxic to man -- Portuguese
Man-O-War
C. food processing
1. tentacles with cnidocytes
2. gastrovascular cavity - incomplete (one opening)
3. digestion by cells -- cells engulf food fragments
through phagocytosis
D. nervous system
1. nerve network in polyps
2. rings of nerve cells in medusas
E. typical life cnidarian cycle
1. characterized by a planula larva stage
2. some alternate between an asexually reproducing polyp
and a sexually reproducing medusa (true jellyfish)
3. external fertilization
II. Phylum Platyhelminthes - flatworms, flukes, and tapeworms;
aquatic free-living forms and parasitic forms
A. exhibit bilateral symmetry
1. efficient locomotion
2. dorsal and ventral surfaces
3. anterior and posterior ends
4. cephalization - head region with sensory organs
a. sensory cells at anterior end
b. ganglia as forerunner of brain
B. triploblastic
1. mesoderm between ectoderm and endoderm
2. give rise to specialized adult tissues
3. solid body with no internal body cavity - acoelomate
C. free-living flatworms - Planaria
1. food processing -- incomplete digestive tract
2. muscular pharynx
3. sensory system - eyespots "ocelli"
4. musculature - muscle cells
5. excretory structures -- flame cells
6. reproductive organs - hermaphroditic
D. parasitic flukes and tapeworms (refer to Figure 29.11, p
550 in Raven & Johnson)
1. organism which causes schistosomiasis - a disease in
which the fluke lives in the intestinal tract, liver, or
bladder causing injury to the organs; 1 in 20 people in
tropical Africa, Asia, South America, and the Middle East
are afflicted with schistosomiasis
2. tapeworms - important parasite of livestock and pets
III. Phylum Nematoda - roundworms; aquatic and terrestrial (soil);
refer to Figure 29.12, p 551 in Raven & Johnson
A. largest group of invertebrates in terms of shear numbers
B. unsegmented round worms
C. characteristics
1. triploblastic
2. first group to have a complete digestive trcct *one-wa{)
3. pseudocoelomates - fluid-filled cavity located between
mesoderm and endoderm (se Figure 29.9 (b), p 549 in Raven
& Johnson)
a. increases the effectiveness of muscles
b. functions as a hydrostatic skeleton
4. dioecous
D. important parasites of man, livestock, pets, and
economically important crop plants
1. Trichinella - contracted from eating poorly cooked
pork
2. heart worms in dogs
3. elephantiasis
4. thick cuticle which prevents digestive enzymes of the
host organism from damaging the roundworm
IV. Phylum Mollusca - gastropods, bivalves (two-shells), and
cephalopods; aquatic (marine & freshwater) and terrestrial; refer
to Figure 29.4, p 553 in Raven & Johnson
A. characteristics
1. soft bodies
2. mantle which secretes a shell
3. triploblastic
4. coelomate - first group to have a true coelom
5. protostome develpoment - refer to Figure 29.13 (a), p
552 in Raven & Johnson
6. complete digestive tract
7. muscular foot used for locomotion
8. cephalopods have arms and tentacles
9. cephalopods also have a "camera" eye - similar to a
mammalian eye
10. mantle cavity which houses respiratory structures --
gills in aquatic mollusks and a primitive lung in
terrestrial snails
11. well developed digestive, excretory (nephridia), and
reproductive systems (trochophore larva)
12. radula - scraping organ similar to a tongue;
secondarily lost in bivalves
B. diversity
1. gastropods - "stomach foot" (Figure 29.14 (a), p 553
in Raven & Johnson) - snails, whelks, conchs, etc
[marine, freshwater, & terrestrial]
2. bivalves (Figure 29.14 (b), p 553 in Raven & Johnson)
- clams, mussels, scallops, etc [marine & freshwater]
3. cephalopods - "head foot" (Figure 29.14 (c), p 553 in
Raven & Johnson [marine]
C. structural features
1. basic body plan
a. head-foot
b. visceral mass
c. mantle and mantle cavity
2. highly developed nervous system in some
D. circulatory system
1. heart and blood vessels
2. open circulatory system in bivalves and gastropods
3. closed circulatory system in cephalopods
V. Phylum Annelida - segmented worms; marine, freshwater, and semi-terrestrial
(live in moist environments); refer to Figure 29,15, and Figure 29.16,
p 554 in Raven & Johnson
A. body divided into segments
1. segments are advantageous -- allow for specialized
movement
2. internal structures -- nerves, nephridia, blood
vessels, and reproductive irgans are repeated in several
segments -- damage to one segement is less harmful to the
functioning of a segmented organism
B. evolutionary link with mollusks
1. trochophore larva
2. coelomate
3. triploblastic
4. protostome development
C. characteristics
1. segmented muscles and coelomic compartments
a. longitudinal and circular muscles
b. bristles (setae) assist in burrowing
2. complete digestive tract and closed circulatory system
3. paired nephridia in each segment for excretory system
4. chainlike nervous system
5. hermaphroditic
6. dorsal blood vessel and ventral nerve cord
D. leeches -- substance in salivary gland which is an
anticoagulant - hirudin (first commercially available blood
thinner); still used in the treatment of burns and the
reattachment of body parts