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G.O. Sars, 1872

Description
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. In females, marsupium with seven pairs of oostegites. Telson cleft.
— Species. Body smaller and much more slender than in Boreomysis tridens and Boreomysis arctica. Carapace with rostral plate without processus; with the anterior margin hardly at all produced and with slightly raised marginal rim, leaving the eyes and eyestalks wholly exposed; antero-lateral angles produced into a very short spine.
Eyes very large, globular, basal part of the eyestalk very slender; no trace of an ocular papilla cornea wider than the eyestalk. Eye pigment, golden brown.
Antennal scale about one-quarter longer than the antennular peduncle, slightly arcuate and narrow, about six times as long as broad, outer margin entire and terminating in a strong spine which projects wholly beyond the apex of the scale, no oblique distal suture, a prominent spine on the outer distal corner of the sympod; second segment of the antennal peduncle with an obtuse distal process tipped by two setae.
Uropod with endopod slightly longer than the telson and having a single spine on the inner margin near the statocyst; exopod nearly one-quarter longer than the endopod and only slightly broader, with narrowly truncate apex, proximal fifth of the outer margin unarmed and terminated by 2 spines from which an incomplete suture runs obliquely across the exopod; statocyst not so small as in the majority of species of the genus.
Telson about equal in length to the sixth abdominal somite, general form long and slender, about three and a half times as long as broad at the base, apex cleft for about one-seventh of its total length, sides of the cleft diverging and armed with a continuous row of long saw-like teeth, no proximal dilation to the cleft; no plumose setae, each lobe armed at its apex with two spines, the outer one much longer and stronger than the inner; lateral margins provided with a continuous series of about 20-25 short spines along the distal three- quarters of their length, the spines obscurely arranged in groups of three or four.

Size
Length of adults of both sexes 17 mm.

Depth range
Hyperbenthic. Boreomysis megalops is found at depths varying from 150 to 475 m and thus occurs in much shallower water than the other Boreomysis species in the area.

Remarks
Boreomysis megalops is one of the most distinctive species of the genus. It may easily be recognised by:

- its rather slender and graceful form,
- its large globular eyes,
- the virtual absence of a rostral plate,
- the slender arched form of the antennal scale,
- the undivided propodus of the endopod of the third to the eighth thoracic limbs,
- the form and armature of the telson and,
- the fact that two pairs of pleopods in the male are modified.

Distribution in the North Sea
Northern North Sea, off W Norway.

World distribution
E North Atlantic: 44-70°N, Mediterranean; coastal, shelf; not nearly so widely distributed as Boreomysis tridens and Boreomysis arctica and it is at present known only from the Coasts of Norway and the Atlantic slope to the West of Ireland and off the North of Scotland (E North Atlantic 44-70°N, Mediterranean; coastal, shelf). It is also known from the Mediterranean.

[After Tattersall and Tattersall, 1951]

Boreomysis megalops