(Smith, 1882)
Short generic diagnosis
Third maxillipede at most but little longer, sometimes shorter, than third pereiopod, its first joint rarely, the second-fourth joints never obviously incrassated in proportion to the joints in the third pereiopod; its two distal joints with numerous bristles along both margins. On the outer uropod the ciliated part never occupies half the exterior margin. The body not very long and slender, the distance between eyestalks and mandibles not very long. The first joint of the antennular peduncle considerably or much longer than third.
Description
Rostrum short, strongly laterally compressed and reaches as far forward as the middle of the corneal portion of the eye. The rostrum is usually provided with two obscure denticles dorsally near the apex; the inferior margin is slightly convex and is furnished basally with a fringe of plumose setae.
Carapace is laterally compressed and about half the length of the abdomen, excluding the telson. It is evenly founded dorsally, and is produced anteriorly.
Antennular peduncle is about one and a quarter times the length of the antennal scale. The wide basal joint is one and a half times the length of the ultimate segment.
Scaphocerite of the male bears a single-jointed appendix, tipped with setae.
Mandible are provided with a long two-jointed palp, which is densely setose; the basal joint is rather less than two and a half times the length of the ultimate.
The first pair of pereiopods, which is not chelate, reaches slightly beyond the middle of the antennular peduncle. The merus is long and about equal to the slender multiarticulate propodus, the dactylus is distinct but very minute and is provided with a single long seta. The second and third pairs possess a minute but perfectly formed chela; the latter are considerably longer than the former, and both when stretched forwards reach beyond the apex of the antennular peduncle. In both, the merus is slightly longer than the carpus, but a little shorter than the multiarticulate propodus. The distal joints of all the first three pairs are provided with setae along both margins, as a general rule long and short setae alternate with one another.
Pereiopods 4 and 5 are much shorter, strongly compressed and laminar, and one of the joints, presumably the dactylus, is missing. The posterior margins of both pairs are clothed with numerous very long plumose setae, and a similar but shorter fringe is found on the anterior margin of the ischium and merus of the fourth and on all the segments of the fifth pair. The fourth pair when stretched forwards reaches to the distal end of the basal peduncular joint. The propodus, or distal segment, is lanceolate and rather less than three times as long as broad; it is about equal in length to the carpus, but is considerably shorter than the merus. The fifth pair is little more than half the length of the fourth and is about two-thirds the length of the carapace. The ischium, merus, and carpus are of about equal length, the lanceolate propodus is considerably shorter.
There are no exopodites on the last two pairs of maxillipeds or on any of the pereiopods.
Telson reaches to about half the length of the outer uropod; it is sulcate above, with a pair of prominent dorso-lateral carinae, and terminates acutely. The inferior margins are finely setose.
Remarks
The corneal portion extends over more than half the length of the whole organ.
Size
Length up to 90 mm.
Colour
Sergia robusta is a species which possesses one of the finest colouring of the deep-water prawns. The blue reflections are very conspicuous and beautiful. Uniform clear scarlet lake, much darker, with bluish reflections, on the anterior portions of the carapace. The antennal scale is scarlet lake with a row of faint crimson spots; similar spots are also found along the basal edge of the sixth abdominal somite and near the apices of the inner and outer uropods. The eyes are jet black, and all the finer setae with which the species is clothed are reddish gold. Sergia robusta is a species which possesses one of the finest colouring of the deep-water prawns. The blue reflections are very conspicuous and beautiful.
Depth range
Pelagic species, down to 4900 m.
Distribution in the North Sea
Northern North Sea.
World distribution
Atlantic Ocean and the Mediterranean.
[After Kemp, 1910]