Phylum Mollusca includes two major classes: Gastropoda (snails, limpets, slugs) and Bivalvia (clams, oysters, mussels, scallops). Mollusks have a visceral mass containing organs surrounded by the mantle and mantle cavity. Gastropods undergo a process called torsion where the viscera twist 180 degrees, pulling the head into the shell for protection. Bivalves have two hinged shells or valves held together by adductor muscles, and use cilia and siphons to filter feed. Many mollusks are threatened by overharvesting, pollution, and loss of habitat.

1. Phylum Mollusca Class: Gastropoda Class: Bivalvia

3. Class Gastropoda Snails, Limpets and Slugs

14. Torsion

17. Class Bivalvia Clams, Oysters, Mussles, Scallops

25. Get ready for dissecfrtion!