New Jersey Scuba Diving
Mollusks - Bivalves
All of these bivalves are filter feeders. The other major group of mollusks is the Gastropods, or snails. Squid and octopus ( cephalopods ) are mollusks too, but they don't behave like other mollusks, so I included them elsewhere. Teredos are bivalves that have evolved a worm-like wood-boring habit.
Typical bivalve anatomy
The inshore wrecks are sometimes surrounded by the empty shells of Surf Clams Spisula solidissima, right, to 7" across. Large numbers of the white shells also wash up on beaches. Surf Clams are found subtidally down to 100 feet ( which makes you wonder why they are called surf clams. )
Tiny angel wing-shaped Coquina clams Donax variabilis less than 1 inch long do live in the surf, on wave-tossed sandy beaches.
Edible Quahogs Mercenaria mercenaria are smaller and darker than surf clams, usually 2-4" across. The tongue-like muscular foot is used to dig in the sand. This is the part that is used in chowders and other recipes. Quahogs are found in shallower water than Surf Clams, generally along beaches and bays.
The incurrent and exhaust siphons of a clam in a muddy bottom ...
... and their owner, a Quahog, next to the hole he was dug out of.
The Razor Clam Ensis directus, to 10" (right) burrows deeply, and can also swim with its long muscular foot. Generally, only dead empty shells are found. Razor Clams are not usually eaten, and are fast diggers that are not easy to catch. They live in sandy mud, subtidal down to 120 ft. There are many other types of clams.
Clamming is one of the last viable fisheries left in New Jersey
A modern hydraulic surf clam dredge
Side-scan sonar image of bottom marks left behind by a clam dredge.
The marks are on the order of one foot deep.
Mussels are found everywhere, attached to any solid substrate. Mussels are to the sea what grass is to suburbia. Mussels lack the muscular foot of clams or the large hinge muscle of scallops. Instead, they have a "beard" of tough fibers near the hinge with which they attach themselves.
The Blue Mussel Mytilus edulis, to 4" ( right ) is the edible mussel. The similar Horse Mussel Modiolus modiolus grows to 6", and is considered inedible. Both types are found from the intertidal zone down to the depths. See entry on barnacles.
The other common type of mussel in our area is the Ribbed Mussel Modiolus demisus, to 4". The Ribbed Mussel is roughly the same shape as the Blue Mussel, but has a ribbed shell instead of smooth. It is usually found in brackish water, in bays, estuaries, and marinas, and is inedible. Freshwater Zebra Mussels are more closely related to clams.
Scallops can swim in spurts by clapping their shells. Water is ejected backwards through openings on either side of the hinge, propelling the scallop in the opposite direction - surprising to see for the first time. When not jetting around, they settle into evenly-spaced shallow pits in the sand.
The Deep Sea Scallop Placopecten magellanicus (right) grows to 8" and is found offshore, generally in water over 100' deep. The smaller but equally edible Bay Scallop Aquipecten irradians, to 3", is found in bays and protected shallow waters. The Bay Scallop has a deeply ribbed shell, while the Deep Sea Scallop has many tiny ribs.
Scallops have many eyes around the edge of the shell, and can see well enough to tell when a diver is coming after them. And they have reason to be worried as well - they taste great raw right out of the shell, and make a great snack on the boat between dives! The edible part is a plug of muscle that opens and closes the shell.
Scallops are still collected commercially using "dredges" like this.
The Christian & Alexa is one of the few big local scallop boats.
The Common Oyster Crassostrea virginica, to 10", is the basis of a major fishery, but they occur only in turbid brackish estuaries, conditions generally not conducive to scuba diving. Oysters once dominated the bottom fauna in our local rivers and bays, but are now all but extinct due to pollution and disease. Attempts are being made to reintroduce them in places, and perhaps someday even re-establish the fishery. Disease-resistant Asian Oysters may be the key to this.
The Mermaid's Purse is not an invertebrate at all - it is a fish egg capsule. The egg capsule of a skate or ray, to be precise. The "horns" are to secure the capsule in seaweed. You may find one with a baby skate growing inside, but most are empty. They are included here with bivalves because they are often found scattered around the bottom like shells, up to 3" long. They certainly don't look like fish !
I make no claim as to the accuracy, validity, or appropriateness of any information found in this website. I will not be responsible for the consequences of any action that is based upon information found here. Scuba diving is an adventure sport, and as always, you alone are responsible for your own safety and well being.
Copyright © 1996-2016 Rich Galiano
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