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G.O. Sars, 1869

Description
— Generic features. The structure of the thoracic limbs is are markedly more unguiculate than in any other genus of mysids. The claw is surrounded by a stiff brush of long, peculiar, microscopically spinose setae, giving a very characteristic appearance which can readily be recognised.
Carapace rather short. Antennal scale with outer margin naked and ending in a thorn, apex obliquely truncate. Eyes well developed.
Labrum much longer than broad, produced anteriorly into very long process.
Mandible molar tubercle feebly developed; maxillae narrow, lobe from the third segment feebly cleft.
Proximal segment of exopod of uropod armed with spines but no setae. Endopod of uropod undivided.
Thoracic endopod markedly unguiculate. First pair of thoracic limbs slender, gnathobasic lobe on the second segment only of the endopod or entirely absent; third pair of thoracic limbs with the endopod not elongated and dactylus and claw well developed; pleopods of female reduced to small, simple, linear plates with a few plumose setae. Exopod of uropod with distinct distal suture. Telson entire.
Three pairs of oostegites in the female.
— Species. Body very slender. Carapace very short, as in S. armata.
Antennal peduncle with inner margin of distal joint in the female armed with three plumose setae. Antennal scale equal in length to antennular peduncle, two and a half times as long as broad, outer margin straight, inner margin convex.
Antennal scale equal in length to antennular peduncle, two and a half times as long as broad, outer margin straight, inner margin convex.
Mandibles with molar tubercles feebly developed.
Thoracic limbs markedly unguiculate. The claw is surrounded by a stiff brush of long, peculiar, microscopically spinose setae, giving a very characteristic appearance which can readily be recognised.
Telson narrowly lanceolate, constricted near the proximal end, margins armed with five or six subequal spines proximal to the constriction, followed by an unarmed gap, the distal three-fourths of margin armed with large spines with three to six smaller spines arranged in series in the intervals between them.
Uropods with endopod slightly longer than telson, inner margin armed with row of spines which increase regularly in size distally and have small spines in series of two or three in the intervals between them; exopod nearly twice as wide as endopod, outer margin armed with 15 to 23 spines, distal segment less than twice as long as broad.

Colour
Transparent with practically no pigment except in the eyes.

Size
This species is very like S. clausii in general form but grows to a much greater length, up to 21 mm (as against 11 mm).

Depth range
Hyperbenthic. 20-260 m. Greatest depths recorded for this species, from 200-275 m.

Remarks
Siriella norvegica is more definitely northern in its distribution than other Siriella species of the North Sea.

Distribution in the North Sea
All North Sea.

World distribution
E North Atlantic: 33-62°N; Mediterranean; coastal to slope.

[After Tattersall and Tattersall, 1951]

Siriella norvegica