Chapter 9 The Mollusks Abalone

Mollusks  Soft bodied  Include the shipworm, snail, clam, mussel, oyster, scallop, abalone, squid, octopus, cuttlefish, chambered nautilus  May or not have a shell  100,000 species

More Mollusk Characteristics  Soft, bilaterally symmetrical bodies  Head, foot, coiled visceral mass (internal organs)  Coelom (body cavity), brain (like the worms)

9.1 Class Bivalvia  Clams, oysters, scallops, mussels  2 shells held together by adductor muscles  Clams are the most common and are fed on by sea stars and predatory snails  You 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 CaCO 3 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 O 2 diffuses into gill membranes and CO 2 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 tract  Mussels excrete byssal threads to keep them anchored to rocks – very strong  Oysters 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 sexes  Females 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