Rostrum a post-frontal spine rising from dorsal carina; tip of rostrum reaching just beyond the frontal margin of carapace.
Carapace slightly less than half the length of the abdomen (telson excluded). A sharp spine is present at the antero-ventral margin of the carapace, at the base of the antenna; the upper boundary of the branchial chamber is marked by a carina, which disappears before the posterior margin of the carapace.
Abdominal somites 1-5 with sharp dorsal keel; somite 6 with dorsal keel on the anterior two thirds only and with lateral carina.
Telson about as long as segment 6 but less than both the inner and outer uropods; dorsally strongly sulcate, deeply forked, with eight or nine pairs of spines which are increasing in length from inner to outer.
Eyes rather large.
Antennal scale rather more than half the length of the carapace, rather less than four times longer than wide, with slightly convex outer margin and terminating in a long and strong apical spine.
Pereiopod 1 reaching beyond tip of antennal scale with more than half the length of the propodus; basis and ischium without ventral spines, basis produced into a baso-anterio point; merus with 10-12 ventral spines; carpus very short, little more than 1/5 of propodus.
Pereiopod 2 reaching beyond pereiopod 1; basis armed with 8-9 ventral spines, ischium armed with two spines; merus with 18-25 ventral spines.
Pereiopod 3 slender , wit very short carpus and dactylus. Pereiopod 4 very short, the minute dactylus with a fringe of stiff setae. Pereiopod 5 almost as long as pereiopod 3 but much stouter; the dactylus is spatulate and bears stiff apical and ventral setae.
All pereiopods with exopods, decreasing in size from P1 to P5.
Uropod with exopod much longer than endopod.
The rostrum in P. tarda has been reported being deformed due to infection by Ellobiopsidae (Sivertsen and Holthuis, 1956 Fig. 17 p. 25).
Total length 70 mm or even more.
Colourless transparent to translucent milky white.
Mesopelagic, but reported from shallow depths also.
Distribution in the North Sea
Northern North Sea, including Skagerrak, entering from the adjacent deeper waters of the NE Atlantic Ocean.
N Atlantic, off NE America, Greenland, Iceland, N Norway, Norwegian west and south coasts.
[After Kemp, 1910]