Phylum Mollusca Part1 Reviewer

CHAPTER 12: MOLLUSCA
 Mollusca is an enormous taxon 2nd only to Arthropoda in number of living species
 Includes many familiar animals such as snails, clams, oysters, mussels, slugs, octopods and squids in seven lining classes
 Mollusca includes the taxa:
 Aplacophora consists of small, wormlike molluscs w/ numerous calcareous spicules rather than a shell.
 Polyplacophorans or chitons have eight shell plates
 Monoplacophorans have a low, conical, limpetlike shell and live in deep water. (The limpet shape appears often in molluscan evolution and includes an uncoiled, caplike, low-profile shell and a large creeping foot)
 Gastropods are the snails and slugs and have a one-piece, often coiled shell and are found in the sea, in fresh water, and on land
 Cephalopods include the squids and octopods and mostly have reduced, absent, or internalized shells.
 The bivalves are the clams and their relatives w/ a shell divided into 2 pieces
 Scaphopods are the tusk molluscs w/ a one-piece tubular shell.
GENERALIZED MOLLUSC
 A marine benthic animal, bilaterally symmetric, dorsoventrally depressed, and ovoid in outline
 The body is divided into:
 Head –anterior, small, poorly defined
 Visceral Mass –large dorsal
 Foot –broad, flat, ventral
 Shell –dorsal shieldlike; can be clamped against the substratum to protect the soft parts from predators.
 This animal is adapted for life on hard, rocky substratum, where it uses its rasplike radula to graze on the biofilm of microscopic algae and other small sessile organisms
 Attaches to the substratum by the muscular foot, w/c it uses to move slowly about in search for foot.
MANTLE
 Dorsally, the body wall over the visceral mass is elaborated to form the mantle or pallium w/c is characteristics of all molluscs
 Mantle epidermis secretes protein, calcium salts, and mucus and is also sensory.
SHELL
 Simple, low, conical cap covering the dorsum of the generalized mollusc
 Originated in the