If you've ever wondered
what a bivalve is or a univalve is, they are both mollusks.
A mollusk is a type of shellfish, and each of these two types
describes what the outer shell is. Either are best purchased
fresh or caught live, although both can be found processed ready
for use in recipes.
Univalves
Univalves
are as the name suggests - 'one' shell or a shell having one
piece. Univalves are also known as gastropods. A mollusk with
a univalve shell has usually a foot and head that live inside
the shell, and can extend or retract outside or inside the shell.
Univalves can live in the water or outside the water.
Examples of univalves
include periwinkles, snails, abalone and conch. Univalves are
often tenderized before cooking, as in the case of abalone and
conch, or cooked lightly to ensure the meat is tender. Univalves
can often be tough and rubber-like if overcooked. Univalves
can be prepared from fresh species, and can also be found processed,
such as frozen, ready for quick preparation in the kitchen.
Bivalves
Bivalves consist
of two shells. Unlike the univalve type of mollusk, the bivalves
generally do not have a head, just the body that resides in
between two shells that open and close at will, usually to feed.
Some have a very long foot that either digs or attaches itself
onto things. Bivalve mollusks can be found as fresh or saltwater
varieties.
Bivalves include
the following: scallops, clams, oysters and mussels. Bivalves
are the most frequently prepared of the two types of mollusks,
and the most common seen on seafood menus. A popular way to
cook bivalves such as clams and mussels is to steam them open
and serve them with the pot liquor and crusty warm bread. Because
bivalves such as clams and mussels are so popular, they can
easily be purchased from neighborhood supermarkets and can be
harvested by hand by local fishermen.
Filter Feeding
Bivalves
Bivalves get their
food by filtering the water around them, pumping in and out
water gathering nutrients and eliminating waste. With this action,
they are filter feeders and as such, are as healthy and tasty
as the water around them. They should be harvested in unpolluted
areas, and in times free of red tide which is the over bloom
of algae in the waters.
What to Look
for When Purchasing Univalves or Bivalves
Both types of mollusks
should be tested to ensure all of them are alive and well before
cooking. Since each has a different outer covering (either one
shell or two shells), each has a different method.
For univalves, touch
the bottoms. Univalves will retract if touched at the operculum,
which is a thin piece of shell that is attached to its foot
that can seal up the shell if needed for protection. Discard
any that do not react.
For bivalves, several
may be open when brought home. Once they are opened they should
close back up when disturbed. To test if a bivalve is alive,
the shells will close shut if they are tapped or touched. Toss
out any that are still open and do not close after purchasing.
