Phylum Mollusca Common Name: Mollusk

1. Amy Ko Joseph Choi Phylum MolluscaCommon Name: Mollusk

2. General Information • Classes: • Monoplacaphora, Aplacophora, Polyplacophora, Schaphopoda, Gastropoda, Bivalvia, and Cephalopoda • Comprised of snails, slugs, octopus, clams, etc. • Around 85,000 living species • Major Characteristics: • Unsegmented soft body • Most have internal or external shell • Have a mantle(fold in body wall that secretes hard protective shell) • Muscular foot and/or tentacles • Have a radula(toothed structure used to grate food) • 2 pairs of gills(except in polmonate shells)

3. Feeding: • Depends on class and surroundings • Slugs and snails eat plants and sometimes other small creatures with their radula • Bivalves eat plankton and algae • Some of the bigger cephalopods eat fish, crustaceans, and other mollusks. • Bivalves have cilia on their gills to feed while breathing • Some bivalve mollusks use suspension feeders to vacuum food particles from the surface

4. Reproduction • For most, sperm and eggs are released into the water and fertilization occurs without contact, but some are hermaphroditic • 1st stage: • Occurs in water column • Sperm flows with the water • Female finds it and fertilizes her eggs • 2nd stage: • Female carries larva for 1-10 months • 3rd stage: • When developed, glochidia are released and drift until they find an acceptable habitat

5. Anatomy • Divided into 2 functional regions: head-foot and visceral jump • Head-foots most visible part, easily seen in snails and slugs • Mostly muscular and covered in cilia for transportation • Visceral makes up rest of body(entirely non-muscular and contains organs) • Most have a shell (thick layer made of calcium carbonate) • Mantle covers visceral mass and shell(if present) • Mantle Cavity: where lungs and gills are

6. Anatomy • Skeletal and muscular: • Large foot, visceral mass and mantle, locomotion well-developed • Calcareous shell, secreted by mantle • Circulatory: • Open circulatory system: blood doesn’t circulate entirely within vessels • Collected from gills, pumped through heart, and released to tissues • Cephalopods have closed circulatory system • Have hemocoel (blood cavity)

7. Anatomy • Respiratory/Nervous: • Most mollusks have a pair of gills • Water enters near bottom and exits near top • 3 kinds of cilia: • 1 drives water current through mantle cavity • Other 2 keep gills clean • 2 main nerve chords(3 in bivalves) • Visceral cords serve internal organs • Pedal ones serve the foot • Brain encircles the esophagus • Octopus has mental capacity likened to that of a domestic cat

8. Anatomy • Digestive: • Mouth, anus, and complex stomach • Food is taken up by cells lining digestive glands arising from stomach, then passed to blood • Undigested stuff is compressed, packaged, and discharged through anus into mantle cavity

9. Class Monoplacophora: • Mollusks with cap-like shells • Live at the bottom of the sea • Single, large, bilateral shell

10. Class Aplacophora: • Small and benthic • Found in deep water • Shell-less • About 320 species

11. Class Polyplacophora: • About 940 species • Common name: “coat-of-armor shells” or sea craclies • Composed of 8 separate valves (shell plates) • Dorsoventrally flattened • Have eliptical, convex dorsally and flattened ventrally body • Distinct head without eyes or tentacles

12. Class Scaphopoda: • Common name: tusk shells • Shelled marine mollusks • Have tusk-like shells that are open at both ends • No eyes, tentacles, or gills • Have tubular mantle that completely encloses body • Have reduced foot used for digging*

13. Class Gastropoda: • “belly foot” snails and slugs • Most diverse class • Over 40,000 species • Well-developed head, tentacles, and pigment eyes • Diversification of habitats

14. Class Bivalvia: • Marine and freshwater • Laterally compressed body enclosed by shell in 2 hinged parts • Examples: clams, oysters, mussels • Majority are filter feeders • No head or radula • Gills evolved into ctenidia(specialized organs for feeding and breathing) • Most bury themselves in sediment

15. Class Cephalopoda • Prominent head and set of arms/tentacles • Common name: inkfish (because they squirt ink) • Around 650 species • Translates to “head-foot” because head and foot are attached to each other • Specialized foot(siphon) enables them to move around quickly (jet propulsion) • Active predators