Diagnosis
Carapace generally oval with a well developed incisure. Adult coloration chocolate brown with a clear window in the pigmentation overlying the well developed lateral compound eyes. There is slight sexual dimorphism in the carapace shape, and the females brood the eggs and early embryos. Males are clearly distinguishable by the extremely long seta on the the endopodite of the second antennae that project well beyond the animal's posterior corner (see Skogsberg, 1920 for a full diagnosis)
Remarks
These are relatively large species (6-7mm) occurring at deep mesopelagic and bathypelagic depths. Two species have been described, Macrocypridina castanea and M. rotundata. The former is broadly distributed in all three major oceans including the Northeast Atlantic. At more southerly latitudes it is replaces by the latter. The size and coloration makes it unmistakable.