Class BivalviaClass Bivalvia

Chapter 12 Chapter 12

BivalvesBivalves

22ndnd largest molluscan class largest molluscan class Includes the clams, oysters, mussels, Includes the clams, oysters, mussels,

and scallopsand scallops Sheetlike mantle and shell with two Sheetlike mantle and shell with two

valves cover valves cover Laterally compress animalsLaterally compress animals Many are edibles, some form pearlsMany are edibles, some form pearls

Con’tCon’t

Most are filter feeders, valuable in Most are filter feeders, valuable in removing bacteria from polluted removing bacteria from polluted waterwater

ShellsShells

Valves – two convex halvesValves – two convex halves Margin of the shell is a proteinaceous Margin of the shell is a proteinaceous

hinge and tongue-groove modifications hinge and tongue-groove modifications call teethcall teeth

Umbo – the oldest part of the shell. Mantle Umbo – the oldest part of the shell. Mantle lays down more shell in concentric lines of lays down more shell in concentric lines of growthgrowth

Shells form as a single structure as an Shells form as a single structure as an embryoembryo

Con’tCon’t

Elastic hinge ligament opens the Elastic hinge ligament opens the valves when certain muscles relaxvalves when certain muscles relax

Adductor muscles (dorsal side) close Adductor muscles (dorsal side) close the shellthe shell

The adductor muscles are the The adductor muscles are the primary defense against predatory primary defense against predatory sea starssea stars

Con’tCon’t

Mantle attaches to the shell around Mantle attaches to the shell around the adductor musclesthe adductor muscles

If sand or a parasite gets between If sand or a parasite gets between the shell and mantle, the shell the shell and mantle, the shell responds by secretes nacre to cover responds by secretes nacre to cover it, forming a pearlit, forming a pearl

Pacific oysters form the highest Pacific oysters form the highest quality pearlsquality pearls

Gas Exchange, Filter Feeding, Gas Exchange, Filter Feeding, and Digestionand Digestion

Gills are lamellae (folded sheets), Gills are lamellae (folded sheets), one end attached to the foot, the one end attached to the foot, the other to the mantleother to the mantle

The ventral portion is inhalant regionThe ventral portion is inhalant region Dorsal region is the exhalant regionDorsal region is the exhalant region