Saturday, 10 May 2008

Another uniqueness

The unusual symmetry of an oyster

One peculiarity sets the oyster apart from other species. Most creatures are asymmetrical. We have two arms and two legs; fish are perfectly aligned left to right or starboard to port, birds have two wings, even most other bivalves, say mussels or clams, have shells that are neatly roughly equal in size. Not the oyster.

The two sides of an oyster shell are radically different. The lower side is cupped, as if it has sagged and leached all the conchilion downwards by force or gravity, although an oyster may choose to grow vertically as horizontally, but the effect is the same. The top shell is flat, or flatter. The explanation is simple enough, but it is unusual.

Just as the waters confused the lawmakers, so the transient environment of the estuary has baffled scientists. An oyster is after all, the one stable creature, in an otherwise completely mobile environment. Biology has often stalled on the underlying challenge of it being almost impossible to draw true and precise comparisons between oysters, even of the same species, raised in one estuary to another, which is another part of their charming uniqueness.

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