A New Species of Fresh-Water Gammaroidean Amphipod (Crangonyctidae) from Southeastern New England

Abstract

A new species, Crangonyx aberrans, belonging to the amphipod family Crangonyctidae, is described from lowland aquatic habitats in eastern Massachusetts. The new species shares characters with both pseudogracilis, with which it is sympatric, and shoemakeri, which occurs along the middle Atlantic Coastal Plain and Piedmont. However, aberrans differs from these two species by possessing a unique arrangement of spines on the dactyl of the gnathopods of females and by the presence of subapical marginal spines on the telson of individuals of both sexes. The relationships between aberrans and other members of the genus are unclear. Although similar to species of the gracilis and shoemakeri groups, aberrans, by having subapical spines on the telson, stands apart from all known species of Crangonyx. Not since Bousfield's (1963) descriptions of Crangonyx floridanus and grandimunus have any new North American species of Crangonyx been introduced into the literature; yet Holsinger (1972, 1977) has remarked that possibly several undescribed species of Crangonyx, particularly forms allied to gracilis Smith, 1871 and pseudogracilis Bousfield, 1958, remain to be described. Two species of Crangonyx are presently known to occur in New England. Crangonyx pseudogracilis is widespread throughout northeastern North America (Bousfield, 1958, 1973; Holsinger, 1972). In southern New England, the species is a common inhabitant of larger rivers and, nearer the coast, of smaller streams (Mills, 1964; Smith, 1977a, 1981, 1982a). Crangonyx richmondensis Ellis, 1940 (sensu lato) also possesses a wide range in northeastern North America that extends into and throughout New England, and northward, in both interior and coastal regions and islands (Bousfield, 1973; Holsinger, 1972; Smith, 1977a, unpublished records). Recently, Smith (1981) reported a population of what appeared to represent an undescribed form of pseudogracilis. Subsequently, more critical examination of larger series of specimens, especially adult females, has revealed that Smith's (1981) C. pseudogracilis pop. b represents an undescribed species. This paper provides a description of the new species, discusses its relationships with other species of Crangonyx, and suggests reasons for its unique distribution. I I thank Drs. Edward L. Bousfield and John R. Holsinger for reading a draft of the manuscript and providing many thoughtful and helpful suggestions. TRANS. AM. MICROSC. Soc., 102(4): 355-365. 1983. ? Copyright, 1983, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.78 on Wed, 22 Jun 2016 06:01:49 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC.