Female body less robust than in the two preceding species, and minutely spiny all over, anterior division evenly vaulted above, and having its greatest width in front of the middle. Carapace very large and tumid, the width considerably exceeding the height, surface finely spinulous, with scattered somewhat larger spines, lateral faces partly mapped out by rows of small spinules into polygonal areas having, as a rule, at each corner an anteriorly-pointing spine, three or four somewhat larger spines forming on each side a lateral series extending forwards to the base of the pseudorostral projection, the hitter of moderate size, conically produced, horizontal and finely spinulose laterally; subrostral corners obsolete.
Exposed segments of trunk each with two very conspicuous juxtaposed spines dorsally forming together a double longitudinal row, epimeral parts of the three posterior segments dentiformly produced. Caudal segments coarsely denticulate both dorsally and laterally. Eye inconspicuous. Superior antennae not much elongated, the peduncle scarcely extending beyond the tip of the pseudorostral projection, its first joint about the length of the other two combined. First pair of legs rather slender, through scarcely exceeding the length of the carapace, basal joint fully as long as the remaining part of the leg, and coarsely spinulous at the edges, the last two joints of about equal length and shorter than the antepenultimate one; second pair with the basal, ischial and meral joints coarsely spinulous, untepenultimate joint rather slender, exceeding the length of the last two combined; third and fourth pairs slender, with the basal joint partly spinulous.
Uropods not much elongated, rami exceeding half the length of the stem, the inner one a little shorter than the outer, and having only six spinules inside (three on the first, two on the second, and one on the last joint), apical spine strong, mucroniform. Telson extending beyond the stem of the uropods, and less narrowed than usual, its proximal half being of nearly uniform width throughout, distal half slightly tapered, and armed on each side with only three spinules, apical spinules a little larger than the lateral.
Adult male, as usual, much more slender than the female, with the carapace less deep and more evenly vaulted above, having on each side behind, a coarsely denticulated lateral keel, which however scarcely extends beyond the middle; anterior part of carapace fringed on each side with a row of densely crowded spinules continued along the side of the pseudorostral projection, lateral faces otherwise nearly smooth, with only very slight traces of the polygonal areas found in the female. Exposed part of trunk with the dorsal spines less distinct than in female. Caudal segments partly denticulate also on the ventral face. The several appendages transformed in the usual manner.
Telson long, with two end spines, postanal part narrowed, with several pairs of lateral spines.
It is an easily recognisable species, being markedly distinguished by the elegant manner in which the spiny armature of the carapace is arranged.
Length up to 11 mm.
Shelf to bathyal.
Depth ranging from 200 to 800 m.
Distribution in the North Sea
NW Europe, off Iceland, Arctic Oceanic.
[After Sars, 1900]