Invertebrates: Phylum Mollusca Molluscs Large and diverse group Coelomates Bilateral symmetry, three germ layers, organ level of organization, tube-within-a- tube body plan

Mollusca cont’d 3 body parts Visceral mass Head/Foot Mantle 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

Diversity of molluscs Fig. 30.10

Mollusca cont’d Class Gastropoda Foot is flattened ventrally 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

Mollusca cont’d Class Cephalopoda Squid, octopus, Chambered nautilus 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

Gastropod and cephalopod anatomy Fig. 30.11

Molluscs cont’d Class Bivalva Clams, oysters, scallops 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

Molluscs cont’d Class 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

Clam, Anodonta Fig. 30.12

Comparison of clam to squid to land snail Table 30.2