Mollusks are soft-bodied animals that usually have an external or internal shell. They are grouped together due to sharing a similar developmental pattern involving a trochophore larva. Most adult mollusks have bilateral symmetry, an open circulatory system, and a body plan divided into a muscular foot, mantle, shell, and visceral mass. The three major classes of mollusks are gastropods, bivalves, and cephalopods.

1. Mollusca

2. Core Concepts Mollusks, Phylum Mollusca, are-soft bodied animals that have an internal or external shell Grouped together due to similar developmental pattern Most of them have a special kind of ciliated larva called a trocophore that swim in open water and feed on tiny floating plants (phytoplanktons)

3. Trocophore larvae are seen in both mollusks and annelids which indicate that they evolved from a common ancestor (although segmentation was lost early in the evolution of mollusks)

4. Most adult members have: bilateral symmetry Open circulatory system (except cephalopods)

5. Body plan consists of four parts: Muscular foot Mantle Shell Visceral mass

6. Divided into 7-9 classes 3 major classes Class Gastropoda (snails, nudibranchs, slugs) Class Pelecypoda (clams, oysters, mussels, scallops) Class Cephalopoda (Squids, octopuses, cuttlefish)

7. Keywords Mollusca Malacology Pelecypoda Gastropoda Cephalopoda mantle cavity Trocophore larva mantle gills Muscular foot internal/external shell Visceral mass radula filter-feeder Sinuses nephridia ganglia Statocyst ocelli (eyespots)

8. General Characteristics Diversity: more than 150, 000 known species Molluscus= soft Soft-bodied animals with a muscular foot that usually contains the mouth and other structure associated with feeding Mantle Thin delicate cloak-like tissue layer that covers most of the mollusk’s body

9. Shell- calcareous (CaCO 3 ) secreted by mantle Visceral mass- beneath the mantle Mantle cavity- extension of the mantle; contains the gills, anus and excretory pore Organ-system level of organization

10. Most adults have bilateral symmetry Complete digestive system Coelomate Triploblastic Open circulation (except cephalopod) Classification: type of foot and kind of shell

11. Digestive system Mostly herbivores, carnovores, filter-feeders, few are detritus feeders and parasites Radula- used for rasping or scraping or drilling to eat Sharp jaws- use by octopuses to break shells Use of poison Filter-feeders- use of feathery gills (sometimes with mucus)

12. Respiration Use of gills or cutaneous respiration (skin) Land snails and slugs- use mantle (High SA, rich in blood vessels)

13. Circulatory System Simple heart Hemolymph (blood + interstitial fluid) Open circulation (sessile) Blood flows into spaces called sinuses Close circulation (fast-moving)

14. Excretory System Nephridia- organ used to remove ammonia in their system

15. Nervous System Nerve ring- surrounds the esophagus Where nerve cords extend Simple nervous system (inactive bivalves) Statocysts- balance Ocelli- eyespots Complex nervous system (intelligent predators)

16. Reproduction Separate sexes in most mollusks Many hermaphrodites External fertilization Internal fertilization (tentacled mollusks, snails) Sequential hermaphroditism Change of sex depending on environmental factors