Diacyclops dimorphus, a new species of copepod from Florida, with comments on morphology of interstitial cyclopine cyclopoids.

Reid J. W. ¹ & D. L. Strayer ²
J. N. Am. Benthol. Soc, 13 (2):250-265 (1994)

Diacyclops dimorphus, new species, was collected from clean sand sediments of the Blackwater River, state of Florida, USA. The new species differs from congeners in that the female has all rami of the swimming legs biarticulate, but the male has most rami biarticulate and the leg 4 exopodite triarticulate.

Only two other species of Diacyclops show comparable extreme reduction of the swimming legs. These are Diacyclops virginianus and Diacyclops trajani (a new name proposed for Speocyclops minutisimus sensu Petkovski 1954).

The swimming leg articulation patterns of all species of Diacyclops are reviewed. This is the first report of consistent sexual dimorphism in swimming leg articulation in Diacyclops. Sexual dimorphism in the swimming legs rarely occurs in the subfamily Cyclopinae. We suggest that preferential reduction in endopodites of posterior legs of smaller cylopines allows the female genital double somite to remain relatively large.
Many interstitial cyclopine copepods possess distinctive morphological features. They are small, have a relatively large genital double somite, and produce relatively large eggs. Typically, their body appendages (antennule. antenna, mouthparts, and swimming legs) are short with relatively few segments, spines, and setae.

1. Department of Invertebrate Zoology, MRC-163, National Museum of Natural History
Smithsonian Institution, Washington, DC 20560 USA e-mail: reid.janet@nmnh.si.edu
2. Institute of Ecosystem Studies, Box AB, Millbrook, New York 12545 USA