Identification
Rostrum acuminate, acarinate and with converging margins lacking marginal spines or shoulders; cervical spines present; areola narrow with 2-3 punctations in narrowest part; male with hooks on ischia of 3rd pereiopods; male first pleopod terminating in 2 subparallel elements less than 25% length of pleopod, curved throughout length but distal 1/3 more pronounced so that apices of both elements directed at about 90 degrees to main axis of pleopod (Page, 1985). [LENGTH: to 50 TCL; to 95 TL] [WIDTH: to 25] (MFG)
O. immunis have characteristically long, slender chelae with a very splotchy coloration, but these features are a bit difficult to use as diagnostic characters without a few reference specimens. The easiest way to distinguish between O. immunis and O. virilis is the notch near the base of the dactyl, or 'thumb' of the cheliped--O. immunis has it, O. virilis does not. (MFG)
Range
O. immunis has a widespread North American native range from southern Quebec, Canada and New England westward across the upper Midwest to Wyoming and eastern Colorado and the Dakotas and south to extreme northwestern Tennessee (Hobbs, 1989; Pflieger, 1996). Montana's eastern plains populations are the furthest reported western extent this species ranges.
Habitat
Lentic environments; Ponds, roadside ditches, and sluggish streams.
Food
This species is an omnivorous detritivore and a scavenger, feeding by shredding large pieces of organic materials and shredding them up.
