ABSTRACT

The common West Indian micromollusk Rissoina catesbyana is the most abundant species of the family Rissoinidae in shallow inshore waters. Little is known about its distribution largely because of taxonomic confusion with other species of the genus. Most reports of the species in the United States have been under the name Rissoina chesneli, a species only known from Jamaica.

The small (3-4mm) gastropods thrive in dense Thalassia beds in sheltered bays and lagoons. They are not found on the reef tract only a short distance away.

Although basically a tropical species, R. catesbyana is able to withstand reduced salinities and temperature. This has enabled the species to spread along the western Atlantic seaboard from southern Brazil to North Carolina. The young hatch out as free-swimming veligers and may be carried for some distance by currents. They are most abundant in areas like Biscayne Bay, Florida, where salinity is somewhat reduced, and may number several thousand live animals per square meter.

R. catesbyana is then an indicator of inshore slightly brackish waters. It is not found in the coral reef tract nor can it penetrate very far into waters of low salinity. Its abundance should make it an excellent animal for further study as an environmental indicator, and its presence in the fossil record should prove to be an excellent clue to past environmental conditions.