G.O. Sars, 1883
— 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 slender than in Boreomysis megalops. Carapace with anterior end of rostral plate rounded and produced in front into a very short, acute, slightly upturned rostrum, with acute point; carapace leaving only a small portion of the last thoracic somite exposed; antero-lateral angles acutely produced.
Eyes very small and downwardly directed; corneal portion occupying only a small portion of the eye and not wider than the stalk; a well-developed ocular papilla on the upper distal surface of stalk near the cornea. Eye pigment, brown.
Antennal scale from one-quarter to one-sixth longer than the antennular peduncle, nearly four times as long as broad, outer margin straight, entire, terminating in a small spine, apex obtusely truncate with a small distal suture.
Uropod with endopod slender, tapering slightly longer than the telson, a single spine on the inner margin near the small statocyst; proximal unarmed portion of outer margin of exopod one-eigth of whole length, terminating by a single spine and marked by a very faint incomplete suture.
Telson long and slender, longer than the last abdominal segment, margins concave in distal two-thirds, armed with a series of prominent spines with small denticles between, the number of denticles increasing posteriorly; apical cleft one-eighth to one-sixth of total length of telson, armed with regular teeth and dilated at the proximal end.
Fresh specimens may be orange.
Length of adult female, by exception, up to 28 mm, of male 20.5 mm.
Boreomysis microps is bathypelagic rather than bottom-living. The depth range varies with times in the day and night and found that is has a daily vertical migration of 400 metres: between 600-200 m depth down to 1200 m.
Boreomysis microps can be easily distinguished by:
- the form of the eye,
- by the long tapering posterior segment of the abdomen, which is longer than the two preceding segments together,
- by the subchelate termination of the endopod of the second thoracic limb and,
- by the long, tapering telson with the cleft dilated at the proximal end. A unique character of the Boreomysis species of the North Sea.
Distribution in the North Sea
Atlantic Ocean: <26-67°N, Indian Ocean, E North Pacific; widely distributed in deep tropical, sub-tropical and temperate waters of the Atlantic Ocean and in the Indian Ocean (Atlantic Ocean < 26 -67°N, Indian Ocean, E North Pacific). It inhabits deeper water than Boreomysis tridens and Boreomysis arctica and it was seldom taken at a less depth than 500 metres.
[After Tattersall and Tattersall, 1951]