— Generic features. Statocyst in the uropods small. Pleopods of female reduced, rudimentary; of male variable. Exopod of uropod with proximal portion of outer margin naked, marked distally by one or two spines and an incipient articulation. Marsupium with seven pairs of oostegites. Telson cleft.
— Species. Body less robust than in Boreomysis tridens. Carapace with rostral plate triangular, pointed; with the anterior margin produced into a median acutely spiniform rostrum which extends beyond the eyes and almost to the end of the first segment of the antennular peduncle; antero-lateral corners of the carapace acutely produced.
Eyes large, pyriform, cornea wider than the eyestalk. Eye pigment, golden to red-brown.
Antennal scale less than twice as long as the antennular peduncle, five times as long as broad, outer margin straight, entire, terminating in a strong spine beyond which the apex of the scale is not produced.
Uropod with endopod slightly longer than the telson and having two spines on the proximal end of the lower inner margin; exopod one-quarter longer and considerably broader, than the endopod with truncate apex; proximal unarmed part of the outer margin equal to one-quarter of the entire length of the exopod and terminated by two spines from which an incomplete suture runs obliquely across the exopod; statocyst small.
Telson longer than last abdominal somite, three times as long as broad at base; apex cleft to one-fourth of the entire length of the telson, margins of cleft slightly diverging, armed with a continuous row of saw-like teeth; no proximal dilation to the cleft; no plumose setae.
Length of adults of both sexes 27 mm.
Benthopelagic. Recorded depths range from 380-2000 m.
Boreomysis arctica is closely related to Boreomysis tridens and the only obvious difference between them is in the form of the rostrum. Minor differences can be detected in the proportions of the antennal scale, 5 times as long as broad in Boreomysis arctic as against 4 times in Boreomysis tridens, in the relatively shorter unarmed portion of the outer margin of the exopod of the uropod, one-quarter of the entire length in Boreomysis arctica as against one-third in Boreomysis tridens.
Distribution in the North Sea
Northern North Sea, off W Norway, Skagerrak, Oslofjorden.
E North Atlantic: 28-79°N, Mediterranean, North Pacific; shelf, slope. Distribution includes the North Atlantic quite similar to that of Boreomysis tridens , namely, in boreal waters extending southwards on the eastern slope from Norway to the Bay of Biscay and on the American side from West Greenland to the coasts of New England. In addition, however, it is known from the Mediterranean and from the North Pacific in the Bering Sea, off Japan and off the Coasts of California. Its geographical range (E North Atlantic 28-79°N, Mediterranean, North Pacific; shelf, slope) is thus wider than that of Boreomysis tridens.
[After Tattersall and Tattersall, 1951]