Phylum: MolluscaPhylum: MolluscaClass: BivalviaClass: BivalviaMussels, Clams, Oysters, Mussels, Clams, Oysters,

ScallopsScallops

Class: BivalviaClass: Bivalvia

(bivalved mollusks)(bivalved mollusks)Scallops are an example of a bivalve. Bivalves have two valves (hinged halves to their shells).

Their foot is extendable and it looks like a tongue. It is normally used for digging, allowing the animal to bury itself. Not all bivalves dig.

This photograph shows the important anatomical structures of a bivalve mollusk.

umbo

Important WordsImportant Words• UmboUmbo – is the oldest part of the shell, – is the oldest part of the shell,

on the dorsal side of the shell (the on the dorsal side of the shell (the point).point).

• Pallial LinePallial Line – is the scar where the – is the scar where the mantle attached.mantle attached.

• Adductor MusclesAdductor Muscles – are the muscles – are the muscles that hold the valves closed and leave that hold the valves closed and leave scars on the anterior and posterior scars on the anterior and posterior end. end.

umbo

footThe foot of this clam is in the extended position. The tip is bent as it searches for sand or mud into which it can dig and pull its entire body, shell and all, beneath the sea floor.

mantle

This scallop’s valves are slightly open. The white tissue on the inside is the mantle. The dark dots are the eyes. Notice the thread-like structures extending from the mantle. Scallop use these for protection. They extend them to entangle predators. The threads can detach while the scallop swims away.

This scallop is swimming. It does so by clapping its valves together. The foot is visible at the top of the picture and the threads are extended. If a potential predator touches those threads it will become entangled in them and they will break off of the scallop.

These are zebra mussels, a European bivalve that was accidentally introduced into the Great Lakes by cargo ships from Europe.

Fishing boats from Lake Erie have accidentally carried zebra mussel larvae to other Ohio bodies of water, including the Ohio River. This species has become a major conservation issue. It is costing Ohio residents millions of dollars per year in damage. Zebra mussels invade Ohio only ten years ago.

Zebra mussels reproduce so fast that in ten years their populations have grown large enough to clog the intake pipes for Cleveland and Toledo’s water supplies. They also clog water intakes for power plants.

Almost all freshwater clams are now extinct in western Lake Erie. Zebra mussels rob them of their food supply. This has taken only ten years.

Types of BivalvesTypes of Bivalves• OystersOysters- are very asymmetrical- are very asymmetrical

Types of BivalvesTypes of Bivalves• ClamsClams- shells have ridges- shells have ridges

Types of BivalvesTypes of Bivalves• MusselsMussels- dorsal ventral is longer - dorsal ventral is longer

than anterior and posterior.than anterior and posterior.

Types of BivalvesTypes of Bivalves• CocklesCockles- valves look like a heart- valves look like a heart

Types of BivalvesTypes of Bivalves• ScallopsScallops- have wings on the umbo - have wings on the umbo

(looks like the symbol of shell gas (looks like the symbol of shell gas station)station)

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