Somatogyrus has a shell that is conical and about 3-6mm high (Thomson 1984).  It's protoconch has numerous fine spiral threads and its columella is generally thickened (Thomson 1984).  Somatogyrus depressus has a grayish black color on its body, top of snout, sides of foot, and dorsal surface of its tentacles (Thomson 1984).  Thomson goes on to describe the posterior base of each tentacle having a grayish patch and the penis is un-pigmented, this is true for most Somatogyrus.  Below is a table that tells about the radula of Somatogyrus depressus, a picture showing the radula, and a picture of its shell.