Alternate Title

Discovery of the Carolina Marsh Clam, Polymesoda caroliniana (Bosc), A Supposed Florida Disjunct Species, in Everglades National Park, Florida

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The presence of disjunct species of animals on either side of the Florida peninsula has been reported by a number of authors. The littorinid mollusk, Littorina irrorata Say, which has a range from Massachusetts to the Rio Grande of Texas, except for south Florida, is one such species (Bequaert 1943). The marsh crab, Sesarma cinereum (Bosc), is another example of an animal with a distribution from Virginia to the western Gulf of Campeche except for a break in southern Florida (Rathbun, 1918). Williams (1965) lists 23 species of crustaceans having interrupted distribution at the Florida peninsula. This report on discovery of a breeding population of the Carolina marsh clam, Polymesoda caroliniana (Bosc) in southern Florida supports the contention by Hedgpeth (1953) that at least some, perhaps many, of the disjunct records may be a result of insufficient collecting in south Florida. The Carolina marsh clam has been assumed to be a typical disjunct species since it was described as such by van der Schalie (1933). It was not included in Marine Shells of Southwest Florida by Perry (1940) nor in Florida Marine Shells by Vilas and Vilas (1945). Abbott (1954) apparently knew of no southern Florida material, and recent examination of collections of this species in the E. S. National Museum provided no material south of New Smyrna on the east coast or Fort Myers on the west coast of Florida. Gunter and Hall (1963) found a breeding colony in the St. Lucie River estuary near Fort Pierce, Florida extending the range nearly 275 km farther south along the Florida east coast but gave no details on the size of the population.

The initial discovery of a single valve of the Carolina marsh clam in extreme southern Florida was made by Tabb and Manning (1961) in deltaic muds at the mouth of the East River where it enters Whitewater Bay in Everglades National Park. Since 1962 sufficient discoveries have been made in Everglades National Park to prove the existence of a breeding population occupying two rather different but adjoining habitats over an extensive area of southern coastal marsh.

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