Carapace length one-fifth body length. Ventrally, carapace housing mouthparts, anterior 3 pairs of pereiopods, and 1 pair of ostegites, if present, on pereiopod 3. Dorsally, pleonite segments smooth and rounded. Bowman, in litt.
Entire family appears to be remarkably uniform in many features.
S. cokei shares characteristics with each of the other six Stygiomysis species. Collected at depths of 10-20 m, in the freshwater layer or occasionally in the upper part of the halocline. Of the female specimens collected, the 6 largest had developing oostegites. Paired ventral oostegites extended medially and anteriorly from coxal plates between pereiopods 3-6. Behavior was observed in a laboratory setting.