invertebrates: phylum mollusca molluscs large and diverse group coelomates bilateral symmetry, three...
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Invertebrates: Phylum MolluscaMolluscs Large and diverse groupCoelomatesBilateral symmetry, three germ
layers, organ level of organization, tube-within-a-tube body plan
30-1
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Mollusca cont’d3 body parts
◦Visceral mass includes most organs
◦Head/Foot Radula: rasping organ for feeding muscular portion used for locomotion
◦Mantle covering that envelopes visceral mass
Mantle cavity: space between the two folds of the mantle
Mantle may secrete a shell
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Diversity of molluscs
Fig. 30.10
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Mollusca cont’d
Class Gastropoda Gastro= stomach Poda = foot
◦Foot is flattened ventrally◦Nudibranchs
sea slugs, lack shell
◦Conchs & snails have a shell Protection, prevents dessication in land snails
◦Aquatic gastropods: have gills,◦Terrestrial gastropods:mantle has lung-
like function
30-4
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Mollusca cont’d
Class Cephalopoda Cephalo = brain poda = foot
◦Squid, octopus, Chambered nautilus
◦Body Structure Foot forms tentacles Powerful beak and radula for feeding Extremely well-developed eyes; complex
behaviors Ink glands- secrete “ink”as defense
mechanism
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Gastropod and cephalopod anatomy
Fig. 30.11
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Molluscs cont’dClass Bivalva
Bi = two valva= shells
◦Clams, oysters, scallops◦Gills enclosed in mantle cavity
Filter-feeders- water enters through incurrent siphon
◦Visceral mass coelom is reduced-pericardial cavity is the only
remains of the coelom
◦Open circulatory system blood not always in vessels “sloshes” around in sinuses Heart pumps blood to dorsal aorta and then to
organs
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Molluscs cont’dClass Bivalva cont’d
◦Lack cephalization nervous system consists of ganglia
connected by nerves
◦Digestive system labial palps, esophagus, stomach,
intestine
◦Excretion by kidneys◦Sexes separate, fertilization
produces a trochophore larva
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Clam, Anodonta
Fig. 30.12
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Comparison of clam to squid to land snail
Table 30.230-10