2000-02 Jumpin' Jehoshaphat!

Encounters Al Hornsby

Among the bivalves—mollusks like clams, oysters and scallops—most all either spend their lives attached to a hard surface or burrowing slowly through sand or mud. A few unusual species, however, can actually jump and swim about, whether to escape their enemies or to move on to greener pastures. Among the most interesting and lovely of these creatures, the Rough File Clam (Lima scabra) is commonly found—though not so easy to spot—on reefs throughout the tropical Atlantic and the Caribbean.

The unique 2- to 31¼2-inch clam hides itself in crevices in the reef, attached to the rock or coral by threads secreted at the rear of its shell. It is found in waters from near shore to several hundred feet deep and is quite frequent at diving depths. Normally all that will be exposed is its mass of white or orange tentacles and its deep red interior, which is actually its blood-rich mantle. While most divers have seen photos of this picturesque animal, few notice them alive on the reef.

Like other clams, the Rough File Clam is born from eggs and sperm released freely into the water in huge amounts by adult clams. The tiny embryo then floats in the water column, being swept about by the currents and tides, until it settles on the bottom and attaches itself, then begins to secrete a hinged shell from its mantle. As it grows, it feeds by extending its tentacles, which are actually gill structures that serve a dual purpose, that of both feeding and respiration. As tiny plants and bits of other organic matter come into contact with the gills, they stick on the mucous covering and are transported to the mouth, located inside the shell.

If you look closely in crevices and cracks on the bottom, you’ll find a surprising number of these small mollusks. If you approach too near, they will snap their shells closed and retreat deep into their refuges. If out of their hiding places, they can swim with surprising energy, jumping jerkily through the water by opening and closing their shells rapidly, moving along edgewise, using their tentacles to maintain position in the water between snaps.

Next time you’re on a Caribbean or Atlantic reef, slow down and take a close look around the bottom. You are likely to be rewarded by finding one of the sea’s beautiful and surprisingly unique creatures.