Chapter 9The Mollusks

Abalone

Mollusks

Soft bodiedInclude the shipworm, snail, clam, mussel,

oyster, scallop, abalone, squid, octopus, cuttlefish, chambered nautilus

May or not have a shell100,000 species

More Mollusk Characteristics

Soft, bilaterally symmetrical bodiesHead, foot, coiled visceral mass (internal

organs)Coelom (body cavity), brain (like the

worms)

9.1 Class Bivalvia

Clams, oysters, scallops, mussels2 shells held together by adductor musclesClams are the most common and are fed on

by sea stars and predatory snailsYou can learn the age of a clam by

counting the bands on its shell– Little lines make up the bands and 1 band = 1

year

Clam Age

Clam Shells

Wider age bands mean a better year with more favorable conditions.

Made of CaCO3 which is secreted by the mantle

Life Activities

Siphons – Incurrent siphon takes in water and food and waste is excreted through the excurrent siphon.

Clams filter food out of the water and O2 diffuses into gill membranes and CO2 diffuses out into waste water.

Clams filter and clean great quantities of seawater

More Life Activities

Open circulatory system with colorless blood

One way digestive tractMussels excrete byssal threads to keep

them anchored to rocks – very strongOysters excrete cement

Movement

Clams dig into sand using muscular foot and extend their incurrent siphon into the water above them

Scallops clap shells together and move by jet propulsion

Reproduction

Separate sexesFemales excrete eggs into the water and

males excrete sperm.Fertilization is external and larva lives as

part of zooplankton population until it forms a tiny shell and settles to bottom