Pseudopaguristes pachydactylus, Rahayu, 2008

Rahayu, Dwi Listyo, 2008, The genus Pseudopaguristes McLaughlin (Crustacea: Decapoda: Anomura: Diogenidae) from the southwestern Pacific, with the descriptions of two new species, Zootaxa 1840, pp. 54-66 : 60-62

Pseudopaguristes pachydactylus n. sp.

( Figs.3–5)

Material examined. HOLOTYPE: New Caledonia, Musorstom IV : Holotype, female, 2.1 mm, stn. DW184, 19º04'S, 163º27.5'E, 260 m, 18 Sep 1985 ( MNHN) . PARATYPES: 1 male, 1.5 mm, 2 females ovig., 1.8, 2.2 mm, same locality as holotype ( MNHN) ; Volsmar : 2 males, 2.1, 2.3 mm, stn. DW 42, 22º17'S, 168º41.50'E, 400 m, 8 Jun 1989, 400m; MUSORSTOM 5: 1 male, 2.2 mm, stn. DW 301, 22º06.9'S, 159º24.6'E, 487–610 m, 12 Oct 1986 ( MNHN) . Norfolk , Smib 5 : 1 male, 2.7 mm, stn. DW 79, 23º41.3'S, 169º01.1'E, 285 m, 7 Sep 1989; 1 male, 2.1 mm, 1 female, 1.5 mm, stn DW 87, 22º18.7'S, 168º41.3'E, 370 m, 13 Sep 1989 ( MNHN) . Chesterfield Islands , Ebisco : 1 male, 2.5 mm, stn. DW 2533, 22º18'S, 159º28'E, 10 Oct 2005 ( MZB) ; 1 female ovig. 3.0 mm, stn. DW 2612, 19º35'S, 158º41'E, 392– 392 m, 19 Oct 2005 ( MZB) .

Description. Gills biserial; branchiostegites each with few small spinules on dorsal margin distally, anterior margins each with 1 spinule.

Shield ( Fig. 3A) 1.2 longer than broad; anterolateral margins sloping; anterior margin between rostrum and lateral projections concave; posterior margin rounded; several spines on dorsolateral surface. Lateral projections triangular, with or without terminal spinule. Rostrum triangular, reaching half length of ocular acicles, with terminal spinule and with sparse, moderately long plumose setae marginally.

Ocular peduncles subequal, left slightly longer, about half length of shield, few setae on dorsal surfaces proximally; corneal diameter 0.5 of peduncular length. Ocular acicles triangular, each with bifid or simple terminal spine; separated basally by approximately basal width of 1 acicle.

Antennular peduncles, when fully extended, as long as left ocular peduncle or slightly overreaching right distal corneal margin. Ultimate segment unarmed; penultimate segment with small spine on ventral surface at approximately midlength. Basal segment with acute spine on dorsolateral margin of statocyst lobe and 1 spine at ventromesial distal angle.

Antennal peduncles not reaching bases of corneas; fifth and fourth segments unarmed; third segment with ventromesial distal angle produced, terminating in acute spine; second segment with dorsolateral distal angle produced, terminating in bifid spine, lateral margin with 1 prominent spine; dorsomesial distal angle with small spine; first segment unarmed. Antennal acicles each reaching to or slightly beyond midlength of fifth peduncular segment, with bifid terminal spine; mesial margin unarmed, lateral margin without or with 1 spine. Antennal flagellum much shorter than carapace; each article with 2–4 moderately short setae.

Coxae of third maxillipeds each with 2 tiny spines on ventromesial margin; ischia each with well developed crista dentata and 1 small spine on ventrodistal margin; meri each with 3 spines on ventral margin.

Chelipeds subequal ( Fig. 3B), with chela somewhat triangular (in dorsal view), armature generally similar; dactyl and fixed finger with narrow hiatus. Dactyl 1.8 longer than palm; dorsomesial margin with row of prominent corneous-tipped spines, decreasing in size distally and accompanied by tufts of moderately long plumose setae, dorsal surface with irregular row of spines and tufts of plumose setae, obscuring armament; mesial face ( Fig. 3C) with proximal and dorsodistal unarmed areas, remainder of surface with irregular rows of small spines, ventral margin with few tufts of setae; cutting edge with row of small calcareous teeth in proximal 0.7, row of corneous teeth distally; terminating in small corneous claw. Palm short, 0.5 length of car- pus; dorsomesial margin with 3 prominent corneous-tipped spines and tufts of setae, dorsolateral margin delimited by row of prominent, semi transparent, corneous-tipped spines; weakly convex dorsal surface with several irregular rows of moderately large spines, each accompanied by tufts of moderately long plumose setae obscuring armament, rows extending to fixed finger; mesial face with row of spines near dorsal margin; ventral surface with row of semi transparent corneous-tipped spines and sparse tufts of plumose setae; cutting edge of fixed finger with row of moderately small calcareous teeth; terminating in large corneous claw. Carpus 0.6 length of merus; dorsomesial margin with row of 5 prominent, corneous-tipped spines, dorsal surface with irregular rows of corneous-tipped spines accompanied by tufts of long setae, dorsolateral margin delimited by row of prominent, corneous-tipped spines; lateral face with row of small corneous-tipped spines and tufts of setae next to dorsolateral margin; mesial face unarmed. Merus with few small spines on distal margin; dorsal margin with subdistal prominent corneous-tipped spines accompanied by sparse short setae, remainder of dorsal margin with row of small spinules; ventromesial and ventrolateral margins each with row of small corneous-tipped spines and long setae. Ischium with row of minute tubercles on ventromesial margin.

Second ( Fig. 4A, B) and third pereopods ( Fig. 4C, D) with dactyls 1.3 length of propodi; dorsal margins each with row of spines, moderately large on second pereopods, minute corneous spines on third, accompanied by tufts of moderately long, sometimes plumose setae; lateral faces each with few tufts of short setae dorsally; mesial faces each with short sulcus proximally, and few short setae; ventral margins each with row of 9 widely-spaced, corneous spines. Propodi as long as carpi; dorsal margins each with row of prominent corneous-tipped spines accompanied by tufts of moderately long plumose setae on second pereopods, third with row of tiny corneous spines arising from low protuberances, and also with tufts of moderately long plumose setae; mesial faces each with transverse rows of 2 or 3 small spines accompanied by moderately long setae on second pereopods, third with longitudinal row of spines near ventral margin and few spines medially; lateral surfaces each with dorsal row of tufts of setae; ventral surfaces each with row of small spinules and tufts of setae on second pereopods, third only with tufts of setae. Carpi 0.7 length of meri; dorsal margins each with row of prominent spines accompanied by long plumose setae on second pereopods, third with 2 prominent spines distally, remainder of dorsal margin with smaller spines also accompanied by long plumose setae; lateral faces each with weak longitudinal sulcus and small spine near dorsal margin on second pereopods, 2 or 3 spines on third; ventral surfaces each with tufts of short setae. Meri each with dorsal row protuberances and tufts of moderately short plumose setae; ventral margins of second pereopods each with row of small spines and tufts of moderately short setae, third with few spines subdistally and with sparse tufts of setae. Ischia unarmed but with sparse setae. Fourth pereopods ( Fig. 3D) each with small preungual process at base of claw, carpi each with dorsodistal spine.

Male first pleopods ( Fig. 5A, B) each with row of moderately short setae on lateral margin of inferior lamella, external lobe overreaching distal margin of inferior lamella; internal lobe short, with long marginal setae. Basal segment of second pleopods ( Fig. 5C, D) with few setae, distal segment with sparse setae distally on endopod, appendix masculina with row of long marginal setae. Female gonopores paired. Brood pouch ( Fig. 5E) oblong, large, covering pleopod 2 and 3. Eggs large, oval, completely shielded by brood pouch, noneyed eggs size 1 x 0.7 mm.

Telson ( Fig. 5F, G) with deep lateral incisions separating anterior and posterior lobes; asymmetrical posterior lobes separated by median cleft; left lobe longer and larger, terminal margin of both lobes with row of moderately large spines and sparse setae.

Color. Unknown.

Etymology. From Greek pachy, meaning thick, and dactylus, for the short and thick dactyls of the chelipeds.

Distribution. New Caledonia, 260– 394 m.

Remarks. Variation which possibly size related is noted in the shape of the male first pleopod. In the small males of P. pachydactylus n. sp (shield length less than 2.5 mm) the distal margin of the inferior lamella of male first pleopod is smooth (fig. 5A, B), while in the larger males (shield length equal or more than 2.5 mm) it has three or four small protuberances (fig. 5E, F).

The distinctive, triangular shape of the chelae, with stout dactyl and short palm as well as the stout second and third pereopods immediately sets P. pachydactylus apart from other regional species. This species resembles P. mclaughlinae described above in having the mesial face of the dactyls of the chelipeds covered by small tuberculate spines. Two significant differences between these species are the shape of male first pleopod and the female brood pouch. In P. pachydactylus the first male pleopod is small, without row of hooked spines or with small protuberances on the distal margin of the inferior lamella, and quite large and oblong female brood pouch that cover the second and third pleopod, and the eggs. In P. mclaughlinae a row of hooked spines on the distal margin of the inferior lamella of male first pleopod is present and the female brood pouch is small and subovate, not covering eggs, which are attached to the setae of tergal thickening of the second and third pleonal somites.

Comparison between specimens of the same size shows that P. pachydactylus has shorter and stouter ocular peduncles, about half length of shield, while those of P. mclaughlinae are longer and slenderer, about 0.7 of shield length. Additionally, P. pachydactylus has transverse rows of spines mesioventrally on the mesial faces of the propodi of the second pereopod and a row of spines near each ventral margin of the third, with some scattered spines medially. In contrast, P. mclaughlinae has two irregular longitudinal rows of spines on the mesial face of each second pereopod and a median row on each third. However, these last two differences can be attributable to intraspecific variation.