The Occurrence of Neomysis Americana in Two New Localities of the South American Coast (Mysidacea)

Abstract

The oppossum shrimp Neomysis americana (S.I. Smith, 1873) is a very com mon mysid species in shallow Atlantic Waters of North America. The distribu tion of this mysid extends from the Gulf of St. Lawrence, Canada (Tattersall, 1951; Wigley & Burns, 1971) to South Carolina and Georgia, U.S.A. (Sikora et al., 1972; Williams, 1972). Later, Williams et al. (1974) gave its range from the St. Lawrence River to Gasp? Peninsula and from southern Newfoundland to St. Augustine, Florida, U.S.A. According to these authors, N. americana extends as far south as Cape Canaveral, Florida. In the same year, Gonzalez (1974) reported on its occurrence on the northern shore of the La Plata River estuary near the port of Montevideo (Uruguay), this being the first record from coastal waters of South America. Later, the species first was cited, as Neomysis sp. (Hoffmeyer, 1983; Hoffmeyer, unpubl.) from Blanca Bay, Argen tina. Recently, it was also observed on the southern shore of the La Plata River estuary (San Boromb?n Bay), Argentina (Mianz?n y Vi?as, personal commu nication). The present paper reports on the occurrence of N. americana in Argentina (Blanca, Anegada and San Boromb?n Bays) and it discusses the morfological variation of the species along its range of distribution (Atlantic coasts of North and South America). The specimens from Blanca Bay were collected during the sampling pro gram for investigating the composition of Zooplankton in the inner area of the bay, from 1979 to 1981. Specimens from Anegada Bay (7 ovigerous females and 1 male) were isolated from macrozooplankton samples (Dr. J. C. Mallo collection 1986-87). Three important characters were measured: carapace length (from rear edge of orbit to posterolateral margin), length and width of antennal scale (ventral view) and the number of spines in the ventral comb-like row on the endopod of the uropod near the statocyst. The general description of N. americana from Blanca Bay agrees with those of Williams et al. (1974) and Gonzalez (1974). On comparison, no significant differences were observed between the northern forms and that from Uruguay.