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Stylocheiron microphthalma Hansen, 1910

Etymology: Stylocheiron - a column/hand; microphthalma - small eyed

Eye: The eye is small and narrow, the upper lobe has only 2 enlarged crystalline cones in a transverse row (Stylocheiron table), 4 cones altogether. The width of the lower lobe : the width of the upper lobe is about 2.75 (S. microphthalma eye & rostrum).

Peduncle of 1st Antenna: As in the generic diagnosis in Higher Taxa (S. microphthalma lappet lacking).

Rostrum: It is produced as an acute process in the female but is a triangular plate in the male (S. microphthalma eye & rostrum).

Carapace: The gastric region is domed and there is a small ill-defined keel at the highest point (S. microphthalma).

Thoracic legs: The 3rd leg has a "false chela" (Stylocheiron-elongated legs) characteristic of the "S. longicorne group", formed of spiniform bristles from the propodal and the dactyl segments.

Abdomen: The 6th segment is rather short, its length : height is about 1.5. In lateral view, the ventral margin curves distinctly upward posteriorly (S. microphthalma ), but not as abruptly as in S. insulare and S. suhmi . The combined length of the 4th and 5th segments is greater than the length of the 6th segment.

Length: Adults are 6-7 mm.

Petasma: The terminal process is blade-like, truncating terminally with the outer distal angle acute, and the inner angle obtuse. The proximal process terminates in a sub-acute tip directed laterally and outward. The lateral process is less broad than the terminal and proximal, and terminates bluntly (S. microphthalma petasma).

Thelycum: Described by Costanzo and Guglielmo, 1991.

Comments: The slender eye of the adult, terminating always in four enlarged crystalline cones (two in transverse row) is characteristic. Immature S. suhmi may also have this characteristic.

The distribution of S. microphthalma is tropical. It occurs In the Indian Ocean between 10°N and 20°S, and southward in the Agulhas current to 30°S, but it is not in the Arabian Sea or Bay of Bengal. In the western Pacific it occurs northward in the Kuroshio system to 40°N. In the eastern Pacific it is lacking in most of the Eastern Tropical Pacific but enters that region in the belt of the North Equatorial Counter Current, 0°-10°N. It appears to be lacking in the Atlantic (S. microphthalma distribution).

S. microphthalma is present above 200 m.


Stylocheiron microphthalma