Sakai, 1961
The carapace is broadly pentagonal in outline, the antero-lateral borders being subparallel in the posterior half; the postero-lateral and posterior borders are confluent with each other, the latter slightly produced in the middle. In Cryptocnemus haddoni, the posterior border is concave. The front is very low and obtusely triangular, the subhepatic regions are inflated, demarcated from the upper hepatic area by an oblique ridge. The middle portion of the carapace is moderately convex, round, and a longitudinal ridge runs from the front down toward the gastric region. The cardiac region is independently convex and its tip is marked with a small tubercle. The marginal surface of the branchial and intestinal regions is very thin but is upturned, forming a lamelliform expansion as in the congeners.
The chelipeds are short and depressed, the merus and carpus are also very short, the propodus is equal to the merus and carpus together and its upper and lower edges are cristate. There is a faint longitudinal ridge in the middle of the outer surface of the carpus and propodus. The fingers are very short, less than half as long as the propodus.
The terminal segment of the male abdomen is sharply pointed. (Sakai, 1961)
Type locality: coast of Kameki near Hayama, Sagami Bay, Japan, 25-30 m.
Range: Japan - Sagami Bay (Sakai, 1961, 1965, 1976), Gokasho Bay, Shima Peninsula (Sakai, 1961), Kii Peninsula (Sakai, 1976a), Nanki Shirahama (Muraoka, 1998); between high and low tidal marks to 30 m.