Platysympus tricarinatus Hansen, 1920: 52–53, pl. 4 fig. 3a–c.
Type material. Syntypes: UZMC. South Island, 62°57’N, 19°58’W. Not seen.
Diagnosis. Carapace with branchial swellings, with 1 pair dorsolateral ridges, in lateral view without dorsal humps. Telson 1.8 pleonite 6, 0.7 uropod peduncles, with1–2 pairs lateral setae. Adult male unknown.
Depth. 219–1659 m.
Distribution. Northeast boreal Atlantic, Mediterranean, Arctic.
Remarks. The most similar species is Platysympus typicus. While there has been discussion of the difficulty in distinguishing P. tricarinatus and P. typicus, because of the similarities in the carapace and the variability in the strength of the dorsal carinae, the two species at present can be differentiated by the presence of lateral setae on the telson in P. tricarinatus. In P. typicus there are no lateral setae on the telson, although the serration of the lateral margins of the telson can be variable in strength.