Singhaplax styrax, Castro, 2007

Castro, Peter, 2007, A reappraisal of the family Goneplacidae MacLeay, 1838 (Crustacea, Decapoda, Brachyura) and revision of the subfamily Goneplacinae, with the description of 10 new genera and 18 new species, Zoosystema 29 (4), pp. 609-774 : 720-724

Singhaplax styrax n. sp.

( Fig. 39 )

Goneplax nipponensis – Takeda & Miyake 1968: 567, fig. 7 [East China Sea]. — Guinot 1971: 1081 [in list] (part). — Serène & Umali 1972: 82 [discussion]. — Takeda 1973a: 13 [in list]; 1973b: 52; 1982: 19 [in list]; 2001: 248, 251, 259 [in list] [ Japan]. — Dai et al. 1986: 377 [in key] (part). — Dai & Yang 1991: 406 [in key] (part). — Miyake 1991: 220 [in list] [ Japan] (part). — Takeda et al. 2006: 205 [in list] [ Japan] (not Gonoplax [sic] nipponensis Yokoya, 1933 ).

Singhaplax nipponensis – Serène & Soh 1976: 18 [discussion].

TYPE MATERIAL. — KARUBAR, stn DW 18, ♂ holotype, cl 4.1 mm, cw 6.7 mm ( MNHN-B 29211). Paratypes: two other males, one mature female, and one pre-adult female specimen from the type locality as listed under Material examined ( MNHN-B 30073).

TYPE LOCALITY. — Indonesia, Kai Islands, 05°18’S, 133°01’E, 205- 212 m.

MATERIAL EXAMINED. — Indonesia. Kai Is , KARUBAR, stn DW 18, 05°18’S, 133°01’E, 205-212 m, 24.X.1991, ♂ holotype, cl 4.1 mm, cw 6.7 mm ( MNHN-B 29211 ) ; 2 ♂♂ paratypes (cl 4.4 mm, cw 7.4 mm; cl 2.4 mm, cw 3.9 mm), 1 pre-adult ♀, cl 3.0 mm, cw 4.6 mm, 1 ♀, cw 5.6 mm ( MNHN-B 30073 ) .

ETYMOLOGY. — From styrax, Greek name for the spike at the end of a spear, noun in apposition, in reference to

the pointed tip of the G1 characteristic of the species.

DISTRIBUTION. — Japan ( Takeda & Miyake 1968, as Goneplax nipponensis ) and now Indonesia (Kai Is). Depth: 110- 212 m.

DESCRIPTION

Carapace ( Fig. 39A ; Takeda & Miyake 1968: fig. 7a, as Goneplax nipponensis ) transversely rectangular, much wider than long (1.6 as wide as long in holotype). Carapace convex, without clear indication of regions. Front slightly convex. Slight notch between front, inner edge of supraorbital border in most specimens (missing in holotype male). Supraorbital borders broad, conspicuously sinuous, smooth, without conspicuous setae (short simple setae in some paratypes). Suborbital borders conspicuously sinuous, with short, acute granules; inner tooth short not visible dorsally or absent. Long, slender, acute tooth on outer orbital angle; tooth anteriorly placed on carapace. Lateral borders beyond outer orbital teeth slightly convex, no anterolateral teeth.

Subhepatic, pterygostomial regions, with low, round tubercles; long plumose setae on pterygostomial region.

Eye peduncles long (0.8 front width), cornea elongated, spherical distal margin, only slightly reniform (not dorso-ventrally flattened, not clearly divided into anterior, posterior portions).

Chelipeds (P1) ( Takeda & Miyake 1968: fig. 7b, c, as Goneplax nipponensis ) unequal in males, equal in pre-adult female (only female with P1); fingers slender, dactylus curved, conspicuously curved in larger chelae of males, slightly shorter than propodus, with blunt teeth; no dark colour on fingers; inner (ventral) margin of propodus smooth. Broad tooth on inner (ventral), proximal margin of carpus; outer (dorsal) margin of merus with conspicuous low to acute tubercles, long plumose setae. Ambulatory legs (P2-P5) long, slender, unarmed, varying number of long simple setae; dactyli long, slender, each with 2 carinae along each side; length of P5 merus 0.5 cl.

Male abdomen narrow, with 6 freely-movable somites plus telson; telson slightly longer than wide. Somite 3 covers most of space between P5 coxae; somite 2 only slightly narrower than somite 3, leaving relatively small portion of thoracic sternite 8 visible. G1 ( Fig. 39B ; Takeda & Miyake 1968: fig. 7d, e, as Goneplax nipponensis ) long, slender, slightly wider basal part with many small denticles, straight distal part with large denticles along outer margin, slightly pointed tip. G2 ( Fig. 39C ) slender, long, slightly longer than G1, curved flagellum longer than proximal part (peduncle), pointed tip.

Mature female paratype abdomen wide, outer margin of thoracic sternites visible. Telson much wider than long. Somite 2 covers space between P5 coxae, somites 1, 2 narrower than somite 3, leaving small portion of thoracic sternite 8 visible. Vulva of mature female paratype round, relatively large, extending from edge of suture 5/6 (displaced, arched to make contact with suture 4/5) to median portion of thoracic sternite 6, vulvar cover absent but slightly thicker outer posterior margin.

REMARKS

Serène & Soh (1976) included Goneplax nipponensis Yokoya, 1933 (as Gonoplax [sic] nipponensis ) in the genus Singhaplax on account of a G2 longer than the G1 and presumably on the general shape of the carapace. They did not examine any material of this species and based their conclusion on observations by Takeda & Miyake (1968). Although the carapace of the specimen illustrated by Takeda & Miyake (1968: fig. 7a) does agree with the characteristic morphology of the carapace and eye peduncles of Singhaplax , the illustration shown in the description of G. nipponensis ( Yokoya 1933: fig. 64) does not. The outer orbital teeth in Yokoya’s illustration are much smaller and shorter than in Singhaplax , and the orbits and supraorbital borders are straight instead of the conspicuously sinuous borders of Singhaplax . The type material of Yokoya’s species appears to be lost. His species clearly belongs to a different genus, possibly Hadroplax n. gen. from the general shape of the carapace. Yokoya (1933: 198) actually placed his new species as “near” Goneplax sinuatifrons Miers, 1886 (= Hadroplax sinuatifrons n. comb.).

The Japanese material examined and illustrated by Takeda & Miyake (1968), on which Serène & Soh (1976) based their conclusion, belongs instead to S. styrax n. sp. The material examined by Takeda & Miyake, a male and a female, was unfortunately not available for examination but the characteristic G1 of their material ( Takeda & Miyake 1968: fig. 7d, e) is identical to that of S. styrax n. sp. ( Fig. 39B ) with the single exception that the apex is slightly more pointed in the Japanese material than in S. styrax n. sp. The G2 of the male, which was not illustrated by Takeda & Miyake, was described as being longer than the G1 as in S. styrax n. sp. All other characters described by Takeda & Miyake agree with those of the new species.

The Taiwan material identified as Goneplax nipponensis by Ho et al. (2004: 659, fig. 6E) appears to be referable to Goneplacoides marivenae ( Komatsu & Takeda, 2003) n. comb. (see Remarks for the latter species).

Singhaplax styrax n. sp. departs from its other congeners by having a male abdomen that is narrower than in any of the species of Singhaplax where the shape of the abdomen is known, a characteristic of Microgoneplax n. gen. (see below). Another difference is that the supraorbital margins ( Fig. 39A ) are not as sinuous as in the remaining known species of Singhaplax . The G2 of the new species is nevertheless long in sharp contrast to the short G2 of Microgoneplax n. gen. and the supraorbital margins are smooth in contrast to the granular margins of Microgoneplax n. gen. The outer orbital teeth are more slender than those of its congeners. The teeth are placed slightly more anteriorly on the carapace than in most congeners, where they are more medi- ally placed on the carapace. Also characteristic of the new species are the long plumose setae along the outer (dorsal) margin of the cheliped meri and on the pterygostomial region.

The vulva of the only mature female in the material examined (cw 5.6 mm; MNHN-B 30073), and the only mature female reliably identified as belonging to Singhaplax , was round and relatively large. It extended from the edge of suture 5/6, which was uniquely displaced and arched to make contact with suture 4/5, thus appearing as if the anterior edge of the vulva extended from suture 4/5. There was no vulvar cover but the outer posterior margin was slightly thicker than the rest of the margin. The vulva of the second female examined, a pre-adult (cl 3.0 mm, cw 4.6 mm; MNHN-B 30073), was barely visible and suture 5/6 was not displaced or arched.

Singhaplax wolffi ( Serène, 1964) n. comb. ( Fig. 40 )

Goneplax wolffi Serène, 1964: 190 [in key], 191, pl. 16, fig. C; 1968: 89 [in list]. — Guinot 1969b: 522 [discussion]. — Serène & Umali 1972: 78 [in key]. — Zarenkov 1972: 233 [in list].

Goneplax wolfi [sic] – Komatsu & Takeda 2003: 1243 [in list].

TYPE MATERIAL. — Dana Expedition, stn 3612, ♀ holotype, cl 2.4 mm, cw 4.2 mm ( ZMUC 8627).

TYPE LOCALITY. — New Caledonia, off east coast, 21°40’S, 165°24’E, 165- 360 m.

MATERIAL EXAMINED. — New Caledonia. Dana Expedition, stn 3612, 21°40’S, 165°24’E, 165-360 m, 27.XI.1928, ♀ holotype, cl 2.4 mm, cw 4.2 mm ( ZMUC 8627).

BATHUS 1, stn DW 687, 20°34.62’S, 165°07.30’E, 408-440 m, 16.III.1993, 1 ♂ cl 2.1 mm, cw 3.5 mm ( MNHN-B 29351).

BATHUS 2, stn DW 715, 22°39.42’S, 167°10.99’E, 202-227 m, 11.V.1993, 1 ♀ cw 4.3 mm (MNHN-B 29432).

BATHUS 4, stn DW 896, 20°15.92’S, 163°51.70’E, 315-350 m, 3.VIII.1994, 1 ♂ cl 2.6 mm, cw 5.2 mm (MNHN-B 29251). — Stn CP 897, 20°15.93’S, 163°51.75’E, 305-350 m, 3.VIII.1994, 1 ♂ cl 2.4 mm, cw 5.0 mm (MNHN-B 29338).

?LAGON, stn 500, 19°04’S, 163°30’E, 225 m, 4.III.1985, 1 pre-adult ♀ (MNHN-B 29366).

DISTRIBUTION. — Known only from New Caledonia. Depth: 165- 360 m.

REMARKS

Serène (1964) described Goneplax wolffi from only one specimen, a small incomplete female collected off New Caledonia and illustrated only by a poor photograph ( Serène 1964: pl. 16, fig. C). Most of the description consisted of a comparison with Goneplax sinuatifrons (= Hadroplax sinuatifrons Miers, 1886 ), to which Serène believed it resembled. The description, however, gives two diagnostic characters unique for Singhaplax that were also present in several more recently collected specimens from New Caledonia: a recurved tooth (“une forte épine aigue [sic], longe et courbe”) on the median portion of the inner margin of the cheliped merus, and two small tubercles (“2 très petits tubercules”) at a prominence found at the anterolateral border of the carapace of the holotype ( Serène 1964: 192).

The examination of the holotype (cl 2.4 mm, cw 4.2 mm; ZMUC 8627 ) confirmed Serène’s description. The holotype and the additional material from New Caledonia, which includes three males, have permitted a more complete characterization .

The G1 ( Fig. 40A ) has a slender distal part, a pointed tip, and a wide, nearly triangular basal part, with small denticles along the outer border. The G2 ( Fig. 40B ) is as long as the G1, slender, with a straight flagellum that is about as long as the proximal part (peduncle), and an expanded tip with a terminal spinule. The male abdomen is wide as in the other species of Singhaplax with the exception of S. styrax n. sp. The vulva of the only mature but small female (cw 4.3 mm; MNHN-B 29432) extended from the edge of a slightly arched suture 5/6 to median portion of thoracic sternite 6. There was no evidence of a vulvar cover.

Each of the anterolateral borders of the carapace of the largest male (cl 2.6 mm, cw 5.2 mm; MNHN-B 29251) had four small tubercles on a short prominence just posterior to the outer orbital teeth, while there were two in a slightly more pronounced prominence in the small female holotype as indicated by Serène. Two small tubercles were present in a small female (cw 4.3 mm; MNHN-B29432) but the prominence of the holotype was absent. A varying number of tubercles and a prominence on each side of the carapace were found in two small males (cl 2.4 mm, cw 5.0 mm, MNHN-B 29338; cl 2.1 mm, cw 3.5 mm, MNHN-B 29351). There was a small triangular inner tooth on each suborbital border of the holotype as well as in the rest of the specimens that were examined.

The cheliped (P1) propodus was short in the holotype and in the small specimens that were examined. It was elongated, however, in the smallest cheliped of the largest male; its largest cheliped was thick and relatively smooth. There were conspicuous tubercles along the inner border of the propodus in the small cheliped of this male. There was a curved tooth on the median portion of the inner margin of the cheliped merus, a character previously indicated for the holotype ( Serène 1964: 192). The holotype and the small specimens examined had a small, acute tooth on the inner, distal angle of the carpus. It was missing in the largest male.

A relatively large yet sexually immature female from New Caledonia (cl 5.5 mm, cw 9.0 mm; MNHN-B 29366) had two acute teeth on the distal half of the inner margin of the cheliped merus, an acute and conspicuous tooth on the inner margin of the cheliped carpus, and a small tooth only on the posterior angle of the carpus of the left cheliped. The fingers were long and shovel-like, and the dactylus and propodus had long setae on the outer margins. The dorsal surface of the carapace had two shallow ridges and two slight prominences just posterior of each of the outer orbital teeth. The outer orbital tooth was similar to those of Singhaplax but not as prominent. These characters depart so much from those in the holotype and five other specimens of S. wolffi that were examined that it seems certain that they are not conspecific, perhaps not even congeneric.

Figures

FIG. 39. — Singhaplax styrax n. sp., ♂ holotype, cl 4.1 mm, cw 6.7 mm, Kai Is, Indonesia, KARUBAR, stn DW 18 (MNHN-B 29211): A, dorsal surface of the carapace; B, left G1, ventral view; C, left G2, ventral view. Scale bars: A, 5 mm; B, C, 1 mm.

FIG. 40. — Singhaplax wolffi (Serène, 1964), ♂, cl 2.6 mm, cw 5.2 mm,north of New Caledonia,BATHUS 4,stn DW 896 (MNHN-B 29251): A, right G1, ventral view; B, right G2, ventral view. Scale bars: A, B, 0.5 mm.