ORCHOMENE LIMODES, NEW SPECIES, A SCAVENGING AMPHIPOD FROM SCRIPPS CANYON, CALIFORNIA: SPECIES DESCRIPTION AND ANALYSIS OF MORPHOLOGICAL VARIATION

Abstract

Orchomene limodes, new species (Amphipoda: Lysianassidae), recently discovered in Scripps Canyon, California, is described and compared to other species within this genus. Intraspecific analysis of morphological variation was performed in order to determine which characters would be appropriate for the description. Thirty-five potentially diagnostic characters were grouped into three types: qualitative, meristic, and morphometric, and analyzed for variation between individuals. The characters found invariant or slightly variable in this study were then used in the diagnosis of the species description. A discussion is presented on this study's relevance to present and future taxonomic work on this genus. A hitherto undescribed species of the genus Orchomene is found in large numbers in Scripps Canyon off La Jolla, California. This species has been the object of various research studies (Meador, 1981; Present and Smith, 1981; Smith and Baldwin, 1982; Smith and Present, 1983) but lacks taxonomic recognition. It is easily caught by the thousands in baited funnel traps at depths of 50-175 m and is readily maintained for months in the laboratory. Individuals are gregarious, seek low light levels, and prefer temperatures ranging between 7?C and 15?C (Meador, 1981). This species has been used as a shallow-water analog of deepsea lysianassids because it exhibits similar behavioral activities (Smith and Present, 1983). Studies of adult morphological variation in the new species, Orchomene limodes, were conducted in order to describe this species accurately, to help elucidate its taxonomic standing, and to identify characters of special usefulness for future taxonomic work within the genus Orchomene. As Schulenberger and Barnard (1976) point out, such studies of morphological variation are especially needed in identification of species within the genus Orchomene. In this group, diagnostic characters primarily involve proportions, lengths, and shapes of appendages and body structures. The nature and extent ofintraspecific variation in these diagnostic characters, however, are essentially unknown. The ready availability of large numbers of specimens of this new species of Orchomene provided an opportunity to survey intraspecific variation.