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Molluscs Study Guide Mollusc Characteristics • Coelom reduced • Most viscera concentrated in dorsal visceral mass • Body covered by thick mantle (epidermis) which forms a cavity • Mantle secretes calcium carbonate shell (or spicules) • Large ventral muscular foot • Radula (band of teeth in esophagus) Class Bivalvia — Clams, etc. • • • • • • Body and foot laterally compressed Shell with two hinged valves Reduced cephalization Edges of mantle usually fused to form siphons Radula lost Marine and freshwater; mostly filter-feeders Kingdom: Animalia Phylum: Mollusca Class: Pelecypoda Order: Eulamellibranchia Family: Veneridae Genus: Venus Species: mercenaria http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/animals/clam.html Practice Slides The next few slides have no labels. Practice using the following clam dissections. Clam with one shell removed and the underlying mantle still in place. Internal features of the clam; the shell and mantle have been removed to show the foot and gills (ctenidia). Internal anatomy of the clam, showing mouth, stomach, intestine, heart, pericardial cavity and musculature. Internal features of the clam. The foot has been opened to show the digestive system and gonads. Anterior end of the clam showing the stomach and digestive gland. Pericardial cavity of the clam showing the heart and the intestine passing through it. The atrium of the heart is visible. Internal anatomy of the clam showing the posterior region. The cavity above the gills leading to the excurrent siphon is visible. View of the siphons of the clam. The incurrent is lower and the excurrent is uppermost. (WHY?) The shell on the left side has been removed. Class Cephalopoda — Squid, etc. • • • • • • • Shell chambered (if present), reduced, or absent Prehensile tentacles surround mouth Mouth with radula and beak Muscular siphon provides jet propulsion Well developed brain, eyes Closed circulatory system Marine Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Order: Teuthida Family: Loliginidae Genus: Loligo Species: brevipenna Notes • Arms are for prey capture and transfer of sperm to female by male. • Tentacles are for holding prey after it is captured. • The pen is the remnant of what feature of most molluscs? • What are chromatophores used for? esophagus Same as Branchial Heart Same as Branchial Heart Male Squid Male Squid Squid Female Squid Female Squid Female Squid Female Squid Female Squid Ganglia Class Polyplacophora — Chitons • Dorso-ventrally flattened and somewhat elongated • 8 dorsal shell plates (valves) • Mantle forms thick lateral girdle (and sometimes covers plates) • Lack eyes, antennae • Marine Kingdom: Animalia Phylum: Mollusca Class: Polyplacophora Order: Amphineura Family: Mopaliidae Genus: Katharina Species: tunicata Chitons (Class: Polyplacophora) Characteristics • Dorso-ventrally flattened and somewhat elongated • 8 dorsal shell plates (valves) • Mantle forms thick lateral girdle (and sometimes covers plates) • Lack eyes, antennae • Marine Chiton (Katharina tunicata) Class Gastropoda — Snails & Slugs • Coiled, asymmetric shell (lost in many) • Visceral mass (gut, nervous system) becomes twisted 90-180° • Muscular, flattened, creeping foot • Head with eyes (may be reduced or lost), tentacles • Mantle highly vascularized; becomes lung • Marine, freshwater, and terrestrial
