Leander tenuicornis

Leander tenuicornis (Say, 1818)

(Figs. 2, 13A)

Material examined. Badouzih, Keelung City, artificial lobster larvae collector, 4 males (pocl 2.6-6.1 mm), 15.XI.1993 (NTOU M01234); same location, 1 male (pocl 5.3 mm), 30.XII.1993 (NTOU M 011230; same location, 1 ovig. female (pocl 6.1 mm), XII.2009 (NTOU M00951); Bitoujiao, New Taipei City, 1 female (pocl 6.1 mm), 15.X.2007 (NTOU M01381).

Diagnosis. Rostrum sexually dimorphic, expanded vertically in female, less than 1.5 times carapace length; rostral formula 2+6–12/5–7; basal antennular segment straight or concave distally, lateral to second segment; stylocerite reaching beyond midlength of basal antennular segment; second pereiopods with carpus shorter than chela, fingers longer than palm, without teeth on opposable margin of fixed finger.

Colour pattern. Body brownish with white and darker spots; white spots particularly dense dorsally and almost aligned as an longitudinal line. Pereiopods and antennal flagella distinctly alternated with brown and white bands.

Remarks. The rostrum of L. tenuicornis is sexually dimorphic being broadly arched in females and slightly ascendant with converging margins in males. All specimens examined herein possess a conical tooth on the fourth thoracic sternite, a feature previously believed to be absent in this species (Chace & Bruce, 1993); comparison with other material of L. tenuicornis from elsewhere in its range also shows that this tooth is also present in all examined specimens.

Ecology. Shallow water, frequently associated with seagrass beds, algae and, in the open sea, floating mats of Sargassum.

Distribution. Near cosmopolitan in tropical and subtropical seas being absent only from the eastern Pacific; now recorded from Taiwan.