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G.O. Sars, 1883

Description
Eye pear-shaped, the upper lobe is much narrower than the lower lobe (~0.55:1.0). There are no enlarged crystalline cones [S.abbreviatum eye & rostrum ].
Peduncle of first antenna: the second and third segments of the peduncle of the first antenna in the female are long and slender, but in the male are short and thicker. There are no lobes, lappets or spines on the peduncle of the first antenna that are species-specific in structure. The upper flagellum is shorter than the lower. The peduncle of the flagellum-bearing endopod of the second antenna is extremely elongate, with the penultimate segment reaching beyond the end of the scale (squama). [S.abbreviatum ped 1st ].
Rostrum a horizontally produced plate reaching about to the anterior limit of the eyes [S.abbreviatum eye & rostrum ].
Carapace with strongly domed gastric region, with a small median keel [S.abbreviatum-f-drawing ].
Thoracic leg 3 elongated and bearing a true chela [S.abbreviatum-f-drawing ] in which the elongate dactyl segment is distally curved and bears a cluster of small grasping teeth. The dactyl segment is opposed by a slender hook of similar length extending from the propodus.
Abdomen: segments 3-4 bear low mid-dorsal keels and segments 5-6 have small mid-dorsal posterior spines [S.abbreviatum ]. The ratio of the sixth segment length and height varies from about 1.65 to 2.0. The sixth segment is markedly longer than the fifth. A photophore is present at the first abdominal segment only.
Petasma: the terminal process is strong, somewhat hollowed distally. The proximal process is shorter, more slender and tapering throughout its length. The lateral process is curved, slender and nearly equal in length to the proximal process [S.abbreviatum petasma ].
Reproduction: nothing is know about the breeding of the species. The female carries 13-22 eggs (Mauchline, 1984).

Length
Adults are 12-17 mm.

Larval stages
S.abbreviatum-A
S.abbreviatum-B
S.abbreviatum-C
S.abbreviatum-D

Remark
S. abbreviatum is a member of the "S. maximum group", along with S. maximum and S. robustum. The narrow upper lobe of the pear shaped eye and the presence of low keels on the third to fifth abdominal segments distinguish this species from S. maximum and S. robustum. These three species are the only members of the Stylocheiron genus that have elongated third legs that terminate in true chelae in which the dactylus articulates against a branch of the propodus.

Ecology
S. abbreviatum is consumed by fishes.

Depth range
The adults occur at a depth of 50-300 m day and night.

Distribution in the North Sea
Regarding its northern distribution limit in the NE Atlantic (50°N), S. abbreviatum is unlikely to occur in the North Sea. However, the species is recorded north of the North Sea, in the vicinity of the Shetlands (S. Hay, pers. com.).

World distribution
S. abbreviatum occurs in the Pacific and Atlantic Oceans, 40°N-40°S and in the Gulf Stream's northern extension to 50°N near Europe. In the Indian Ocean it is present between about 12°N and 40°S; also in the Red Sea.

[After Brinton et al., 1999]

Stylocheiron abbreviatum