Genus Boninpagurus Asakura & Tachikawa, 2004

[New Japanese name: Okinawa-akashima-hon-yadokari-zoku]

Boninpagurus Asakura & Tachikawa, 2004: 157 .

Type species. Boninpagurus acanthocheles Asakura & Tachikawa, 2004 [= Boninpagurus pilosipes (Stimpson, 1858), n. comb]. Original designation.

Emended diagnosis. Eleven pairs of biserial phyllobranchiate gills, including 2 pairs of arthrobranchiae above bases of third maxilliped to fourth pereopod and 1 pleurobranch on seventh thoracic somite (above base of fourth pereopod). Rostrum (Fig. 2 A) broadly triangular, not particularly developed. Ocular acicles (Fig. 2 A) each with submarginal spine. Antennal peduncle (Fig. 2 A) with supernumerary segmentation; acicles well developed. Maxillule with produced external lobe on endopod (Fig. 2 B). Third maxilliped with well developed crista dentata consisting of fine row of corneous teeth and accessory tooth on ischium (Fig. 2 D). Chelipeds distinctly unequal with right longer and stouter than left (Figs 1 A–C, 3, 4A, C). Second and third pereopods generally similar (Figs 1 A–C, 4D, E). Fourth pereopods semichelate, lacking preungual process on dactylus; propodal rasp of more than 2 rows of corneous scales (Fig. 2 E). Fifth pereopods chelate. Coxa of right fifth pereopod in male bearing sexual tube of medium length, directed laterally or posterolaterally (Fig. 2 G, H, L); coxa of left fifth pereopod with short protrusion of vas deferens (Fig. 2 J). Female with paired gonopores. Male pleon with 3 unequally biramous left pleopods; female pleon with 4 unequally biramous left pleopods. Telson (Fig. 2 K) with lateral indentations; posterior lobes separated by median cleft, left larger; terminal margins oblique, each with spines.

Remarks. The original generic diagnosis of Boninpagurus given by Asakura & Tachikawa (2004) contains a few minor discrepancies or inconsistencies, and therefore is slightly emended herewith. The rostrum was described as “well developed”, but examination of the present series of specimens has shown that the rostrum is usually broadly triangular, not showing particular development. The original authors stated that the propodal-carpal articulation of the left cheliped was rotated counter-clockwise 30° from the horizontal plane, but we found no particular degree of rotation in our specimens.

As noted above, males of the newly collected specimens from Okinawa Islands have the right sexual tube of a medium length (about 5.0 times of the coxal length; see Fig. 2 C). In every diagnostic aspect, Pagurus pilosipes agrees with the diagnosis of Boninpagurus given by Asakura & Tachikawa (2004), and thus the species is herein transferred to Boninpagurus . As dicussed below, conspecificity between B. pilosipes and B. acanthocheles is strongly supported by comparisons of morphology and barcoding gene.