 Soft-bodied animals covered by a mantle  Most secrete a shell to protect the soft body  Coelomates in addition to a mantle cavity

 Head-foot  Mouth and other sensory organs  locomotion  Visceral Mass  Contains heart, digestive organs, excretory organs, and reproductive

 Gastropod (univalve)  Largest most diverse  Only class with terrestrial members  90,000+ species  1 or no shell Twisting of shell lowers center of gravity Torsion –twisting 180 degrees brings mantle cavity forward allows snail to bring head in for defense In some gastropods, an operculum seals off the shell Open circulatory system Blood –like fluid called hemolymph Small to no blood vessels, fluid filled space called hemocoel

Nudibranch ( naked gill ) “sea slugs” -Shed their shell in lieu of toxic defenses - Acquire many of these toxins as a result of diet about 3,000 species Live only about 1 year and because there is no shell, leave very little evidence National Geographic Magazine - NGM.com

 Bivalvia  Two shells joined by hinge  Adductor muscles hold shell together  Incurrent and excurrent siphon for filter feeding  Burrow under sand; attach to substrate  No head

 Octopus, Squid  No shell  Compensation:  Internal cartilaginous support  Fast locomotion – jet propulsion  Image forming eyes  Closed circulatory system (3 hearts)  Ink decoys, camoflauge Blue ringed octopus size of a golfball up to 8in, no known antidote, loss of senses, then unable to breathe