A new stygobiotic species of Diacyclops Kiefer, 1927 (Copepoda, Cyclopidae) from caves in New Mexico, United States

Abstract

A new species of the freshwater cyclopine copepod genus Diacyclops is described from a North American cave system in SE New Mexico, U.S.A. The new species, D. nikolasarburni n. sp., differs from its congeners by its having of a unique combination of characters including: 17-segmented antennules, three-segmented rami in legs 1-4, a basic 2333 spinal formula with a highly variable pattern, naked inner margin of caudal rami, but dorsal surface with spinules, subequal terminal spines of leg 4 endopod, and inner spine of fifth leg about as long as bearing segment. This species has also a variable length/width ratio of the caudal ramus (4.6-6.0, average 5.0); the lateral caudal seta is inserted on the distal one-quarter of ramus. The 2333 spinal formula was dominant (55%) in the population but other patterns were also present. The new species belongs to Group 1 species of Diacyclops (sensu Reid & Strayer, 1994). The local population of this stygobiotic species probably resulted from radiation-stranding processes of epigean forms of widely distributed Diacyclops and is probably endemic to this cave system.