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Stylocheiron indicum Silas and Mathew, 1967

Etymology: Stylocheiron - a column/hand; indicum - of India

Eye: The lower lobe is somewhat higher than wide, and 1.5-1.9x wider than the upper lobe. The upper lobe is without conspicuously enlarged crystalline cones, but 14-16 cones can be seen in a distal transverse row (S. indicum eye & rostrum, Stylocheiron table). In specimens of the same eye width (lower lobe), the upper lobe is about 10% wider in males than in females (Mathew, 1980a).

Peduncle of 1st Antenna: The 1st segment has an acute spine mid-ventrally at its distal end in the adult (S. indicum lappet), otherwise as in generic diagnosis in Higher Taxa.

Rostrum: In dorsal view it is sub-acute, almost rounded, not spiniform, in both sexes, reaching beyond mid-point of the eye (S. indicum dorsal head). It is slightly longer in the female than in the male, and is of the same shape.

Carapace: The gastric region is a low dome (S. indicum), with a low mid-dorsal keel which is relatively longer than in other species of the "S. longicorne group".

Thoracic legs: The 3rd leg has a "false chela" (S. indicum thoracic leg) formed of bristles from the propodal and dactyl segments. 5 of the 6 bristles of the dactylus curve inward; an elongate bristle on the inner margin of the dactylus is of irregular curvature and directed inward, opposing the long propodal bristle of the false chela.

Abdomen: The 6th abdominal segment is long, about 2.0-2.5x as long as high with the segment's length being proportionally greater than its height in females. The ventral margin of the 6th segment is evenly curving throughout its length. The combined length of the 4th and 5th segments is slightly greater than the length of the 6th segment (S. indicum).

Length: Adults are 8.25-13.75 mm, the largest specimens being females.

Petasma: The inner lobe has a rudimentary spine on its inner proximal margin, as in e.g. S. suhmi, S. insulare and S. elongatum . The terminal process is uniformly broad and distally curved as a short hook, narrowing to an acute tip. The proximal process is slightly shorter than the terminal, tapering to an acute tip with its distal one-third strongly bent outward. The lateral process is minute, as in S. elongatum, and pointed, hardly one-sixth the length of terminal process (S. indicum petasma).

Thelycum: Described by Costanzo and Guglielmo, 1991.

Comments: The eye structure and shape of the frontal plate are characteristic. The 6th abdominal segment is as long as in S. longicorne North Indian Ocean Form. That characteristic led Brinton (in Brinton and Gopalakrishnan, 1973) to incorrectly identify that form of S. longicorne as S. indicum.

The three known localities are associated with slope waters on the southwest coast of India near Cochin, the western Philippines, and the Moluccas at the equator (S. indicum distribution).

The only known adults were caught in tows to 300-500 m depth off southwest India. Juveniles from near the Philippines and Moluccas were caught above 200 m.


Stylocheiron indicum