Carcinoplax fasciata, Ng, Peter K. L. & Kumar, Appukuttannair Biju, 2016

Ng, Peter K. L. & Kumar, Appukuttannair Biju, 2016, Carcinoplax fasciata, a new species of deep-water goneplacid crab from southwestern India (Crustacea: Decapoda: Brachyura: Goneplacoidea), Zootaxa 4147 (2), pp. 192-200 : 193-199

Carcinoplax fasciata n. sp.

( Figs. 1–4 )

Material examined. Holotype male (25.8 × 19.3 mm) (DABFUK), Neendakara fishing harbour, Kerala, southwestern India, 450–500 m, 8°38'N 76°14’E, Arabian Sea, western Indian Ocean, coll. B. Kumar, from trawler, 27 November 2015.

Comparative material. Carcinoplax specularis Rathbun, 1914 : holotype male (23.0 × 16.7 mm) ( USNM 46164 ), station 5113, Sombrero Island, off southern Luzon, Philippines, 13°51'30"N 120°50'30"E, 159 fathoms, coll. Albatross, 17 January 1908 . Carcinoplax verdensis Rathbun, 1914 : holotype ovigerous female (13.0 × 10.5 mm) ( USNM 46167 ), station 5119, Verde Island passage, Sombrero Island, Philippines, 13°45'05"N 120°30'30"E, 394 fathoms, coll. Albatross, 21 January 1908 .

Diagnosis. Carapace transversely rectangular; dorsal surface distinctly convex, smooth, without setae or granules; external orbital angle dentiform; front entire without median notch; anterolateral margin with 2 prominent spiniform teeth, tip of first tooth hooked; supraorbital margin with median notch, lateral end of margin with small knob-like tubercle just before external orbital tooth; last anterolateral tooth separated from posterolateral margin by distinct concavity; posterolateral margin gently but distinctly convex; third maxilliped with anteroexternal margin of merus slightly auriculiform, ischium elongate, subrectangular; dorsal margin of palm with low, rounded, crest-like structure; outer surface of palm rugose; distal inner angle of cheliped carpus with acute tooth; ambulatory legs moderately long, slender; thoracic sternum relatively wide, surface covered with short pubescence; male pleon triangular, somite 6 distinctly subrectangular, slightly wider than long; G1 relatively stout, almost straight, proximally broad; base with subrectangular process on outer part; distal part laterally flattened, subtruncate, forming flap-like structure from dorsal view; distal surfaces with numerous short spines; G2 slender, longer than G1. Female unknown.

Description of male holotype. Carapace ( Figs. 1 A, 2A) transversely rectangular, 1.3 times wider than long; dorsal surface distinctly convex, smooth, without setae or granules; regions poorly defined, epigastric region barely indicated, gastro-cardiac groove broad, shallow; external orbital angle distinctly dentiform, triangular, sharp, not extending to frontal margin. Front ( Figs. 1 A, 2A, 3A, B) lamellar, gently sinuous, lined with small granules, entire without trace of median notch; postorbital crest prominent, distinctly granulated, subparallel with frontal margin; front separated from supraorbital margin by small but distinct right-angled notch. Anterolateral margin ( Figs. 1 A, 2A) convex, with 2 prominent spiniform teeth, margins lined with small granules; first tooth acute, directed anteriorly with hooked tip, second tooth larger, acute, sharp, directed obliquely laterally; anterolateral margin separated from posterolateral margin by distinct concavity; posterolateral margin gently but distinctly convex, converging towards gently sinuous posterior carapace margin. Orbit short, ovate, much shorter than front ( Figs. 1 A, 2A, 3A, B); ocular peduncle stout, cornea large, round. Supraorbital margin ( Figs. 1 A, 2A) concave, lined with small rounded granules, with median notch, lateral end of margin with small, rounded knob-like tubercle, just before external orbital tooth. Suborbital margin ( Fig. 3 A, B) concave, entire, distinctly granulated, with low inner tooth near base of eye. Suborbital, subhepatic, anterior half of pterygostomial regions ( Fig. 3 A, B) covered with distinct small rounded granules. Basal antennular article ( Fig. 3 A, B) subrectangular; article 3 rectangular, distal margin touching frontal margin; article 4 shorter than article 3; flagellum long, folding transversely. Basal antennal article ( Fig. 3 B) mobile, short, quadrate, third article touches frontal margin. Epistome ( Fig. 3 A, B) longitudinally narrow; posterior margin of epistome with prominent triangular median projection, which has long longitudinal fissure; lateral margin prominently concave, with long fissure. Endostomial ridge distinct, long.

Third maxillipeds ( Figs. 2 B, C, 3B) almost completely closing buccal cavern when closed; merus quadrate, anteroexternal margin slightly auriculiform, median part depressed; ischium elongate, subrectangular, with submedian oblique sulcus, inner margin lined with dense stiff setae; exopod stout with prominent subdistal triangular tooth on inner margin, with long flagellum.

Chelipeds (P1) ( Fig. 1 A, 2A, 3C–F) unequal, right chela slightly larger; fingers relatively slender, shorter than palm; dorsal margin of palm forming low, rounded, crest-like structure, no trace of window-like ovate structure; outer surface of palm rugose with distinct punctae; inner surface smoother, with gently swollen longitudinal median part, ventro-proximal part with low lobiform rounded projection; pollex of major chela with distinct submarginal sulcus on outer surface, cutting edge with prominent small, large teeth; dactylus with 2 longitudinal sulci on outer margin cutting edge with prominent small, large teeth, basal one gently curved, fitting into concavity on distal margin of palm; fingers of minor chela similar to those on major chela except dactylus without curved basal tooth; carpus rounded with prominent acute, sharp tooth on distal inner angle; merus short, trigonal in crosssection, dorsal margin with prominent curved tooth on distal third.

Ambulatory legs (P2–P5) ( Figs. 1 , 2 A, 3G, H) moderately long, slender; P3 longest; P2–P5 merus subcylindrical, outer surface gently rugose, glabrous, ventral margin smooth, dorsal margin lined with small uneven granules, appearing gently serrated, smoothest in P5; P2–P5 carpus elongate, outer surface glabrous, proximal part of dorsal margin smooth, distal part with small granules; P2–P4 propodus of long, laterally flattened, with distinct shallow longitudinal median sulcus, lateral margins of distal third with short setae which do not obscure margin; P2–P4 dactylus elongate, falciform, entire surface except for sharp tip covered with short pubescence, otherwise smooth; P5 shortest, ca. 0.5 carapace length, when folded reaching to second anterolateral tooth, propodus longitudinally ovate with median sulcus, lateral margins lined with numerous long setae, dactylus relatively shorter than on other legs, with setae relatively longer; dactylo-propodal lock not prominently developed.

Thoracic sternum ( Figs. 1 B, 2C, D) relatively wide, surface smooth, covered with short pubescence; sternites 1, 2 completely fused, triangular, lateral margins gently sinuous, separated from sternite 3 but distinct gently sinuous suture; sternites 3, 4 fused with only lateral part of suture visible; sutures 4 / 5, 5 / 6, 7/8 medially interrupted, suture 6 / 7 complete; distinct median longitudinal groove extending across sternites 7, 8. Posterior edge of episternite 7 partially overlapping anterior part of P5 coxa. Sterno-pleonal cavity deep, extending to about half length of sternite 4, reaching imaginary line connecting proximal part of coxae of chelipeds; with deep longitudinal depression on sternite 4; pleon completely covering sternite 8 when closed. Press-button male pleonal locking mechanism present as short spur-like tubercle on anterior quarter of sternite 5. Opening for penis coxal, at anterior edge of condyle of P5 coxa; penis short.

Pleon ( Figs. 1 B, 2C, D) triangular, all somites, telson free; telson triangular, lateral margins almost straight; somite 6 subrectangular, slightly wider than long, lateral margins gently sinuous, gently converging towards telson; somites 3–5 trapezoidal, somite 3 widest, edges overlapping P5 coxae; somites 1, 2 longitudinally narrow, reaching to P5 coxae.

G1 ( Fig. 4 A–D) relatively stout, almost straight, proximally broad; base with subrectangular process on outer part, lined with long setae; distal part laterally flattened, subtruncate, forming flap-like structure from dorsal view; distal surfaces with numerous short spines. G2 ( Fig. 4 E, F) slender, longer than G1, distal segment long, about half length of basal segment, tip weakly bifurcated.

Colour in life. When freshly collected ( Fig. 1 ), dorsal surfaces of carapace and chelipeds bright orange; tips of anterolateral teeth and cheliped carpal spine white; fingers of chelipeds mostly white except for orange base, distal third light brown; ambulatory legs with dorsal surfaces mostly orange except for white patches on propodus, ventral surfaces paler; prominent red band present that stretches from ventrum of posterolateral carapace margin to below frontal margin; rest of ventral surfaces pinkish-white. This colour pattern is unique amongst the species of Carcinoplax where colour in nature is known.

Etymology. The name alludes to the prominent red band that spans the frontal and lateral parts of the carapace, which is diagnostic of the species.

Remarks. It is unfortunate that no female specimens of the new species are available as one of the diagnostic characters for Carcinoplax H. Milne Edwards, 1852 , s. str. is the large and expanded vulvae which do not have a cover or operculum (see Castro 2007: fig. 1). Carcinoplax fasciata n. sp. belongs to a group of species in which the carapace is distinctly more rectangular (rather than quadrate or subovate), with the dorsal carapace surface smooth, the external angle prominently developed into a distinct triangular tooth which does not reach the entire frontal margin, and the two anterolateral teeth are acute, slender and directed anteriorly with the tips hooked.

The new species is perhaps most similar to C. specularis Rathbun, 1914 (= C. verdensis Rathbun, 1914 ; C. polita Guinot, 1989 ) from the Philippines, Japan, Indonesia, Vanuatu, Solomon Islands, New Caledonia, Fiji, Tonga and Maldives ( Castro 2007: 642) but can be separated by several distinct characters. In C. fasciata n. sp., the anterolateral teeth are more acute and the tip of the first tooth is distinctly hooked ( Figs. 1 A, 2A, 3B) (distinctly broader and more triangular in shape in C. specularis , cf. Fig. 5 A; Guinot 1989: pl. 8A, B); the gastric and branchial regions are more inflated, with the posterolateral margin distinctly more convex ( Figs. 1 A, 2A) (branchial regions less inflated with the posterolateral margin slightly convex to almost straight in C. specularis , cf. Fig. 5 A, C; Guinot 1989: pl. 8A, B); the third maxilliped ischium is proportionately longer ( Fig. 2 B) (relatively more quadrate in C. specularis , Fig. 5 B); the inner distal angle of the cheliped is armed with an acute spine ( Figs. 1 A, 2A, 3C, D) (versus broader and more dentiform in C. specularis , Fig. 5 A); the chelae are less prominently inflated with the dorsal margin not distinctly crested and there is no window-like ovate structure present ( Figs. 1 A, 2A, 3C, D, F) (chelae prominently inflated in adult males with the dorsal margin prominently crested in C. specularis , cf. Fig. 5 A; Guinot 1989: pl. 8A, C, D); pleonal somite 6 is distinctly broader ( Fig. 2 C) (longitudinally more narrow in C. specularis , Fig. 5 D); the G1 is relatively more slender and longer with the distal part subtruncate ( Fig. 4 A–D) (proportionately shorter, stouter with the distal part resembling a bird’s head in C. specularis , cf. Guinot 1989: fig. 34A); and the G2 distal segment is proportionately shorter ( Fig. 4 E) (distinctly longer in C. specularis , cf. Guinot 1989: fig. 34B). The above differences are also valid for the two junior subjective synonyms of C. specularis ( C. verdensis and C. polita ), except for the presence of a window-like ovate structure on the dorsal part of the chela which is found only in C. specularis . Unpublished data by P. Castro, L. Corbari and the first author suggests C. specularis is a species complex; and the matter is now under study.

Compared to the allied C. uncinata Castro, 2009 , from New Caledonia, the anterolateral margin of C. fasciata n. sp. is relatively longer ( Figs. 1 A, 2A) (relatively shorter, with the first anterolateral tooth closer to the external orbital angle in C. uncinata , cf. Castro 2009: fig. 1A); the anterolateral teeth are more acute and the tip of the first tooth is hooked ( Figs. 1 A, 2A, 3B) (distinctly broader and more triangular in shape in C. uncinata , cf. Castro 2009: fig. 1A); male pleonal somite 6 is subrectangular in shape (trapezoidal in C. uncinata , cf. Castro 2009: fig. 1B); and the G1 is relatively more slender ( Fig. 4 A–D) (proportionately stouter in C. uncinata , cf. Castro 2009: fig. 1C); and the G2 distal segment is proportionately shorter ( Fig. 4 E) (distinctly longer in C. uncinata , cf. Castro 2009: fig. 1D).

Carcinoplax fasciata n. sp. also resembles C. longipes (Wood-Mason, in Wood-Mason & Alcock, 1891) (see Huys et al. 2014, for authorship and dates) in its carapace form. The C. longipes as figured in Alcock & Anderson (1895: pl. 14 fig. 7) in the Investigator plates from the Andamans differs from that shown in Serène & Lohavanijaya (1973: 65 [part], pl. 14D), Guinot (1989: 303, pl. 10A–C) and Castro (2007: 636) from the Andamans and Philippines in having more triangular anterolateral teeth and distinctly shorter ambulatory legs (see Castro 2007: 637). It is possible that the type material is mixed and contains two species. From C. longipes s. str. (as defined by Guinot 1989; Castro 2007), C. fasciata n. sp. differs in having the tip of the first anterolateral tooth hooked ( Figs. 1 A, 2A, 3B) (straight or almost so in C. longipes , cf. Guinot 1989: pl. 10A, B); the ambulatory legs are proportionately shorter, with the merus of P5 only reaching to the second anterolateral tooth ( Figs. 1 A, 2A) (P5 merus reaching beyond the second anterolateral tooth in C. longipes , cf. Guinot 1989: pl. 10A); the fingers of the chela are shorter than the palm ( Fig. 3 C, D, F) (fingers longer than the palm in C. longipes , cf. Guinot 1989: pl. 10C); the G1 is proportionately more slender and longer, with the distal part subtruncate ( Fig. 4 A–D) (shorter and stouter with the distal part more dilated in C. longipes , cf. Guinot 1989: figs. 35A, 36A); and the G2 distal segment is distinctly shorter ( Fig. 4 E) (proportionately longer in C. longipes , cf. Guinot 1989: figs. 35b, 36B).

Castro (2007: 641) listed two ovigerous female specimens of C. specularis from the Maldives (The Natural History Museum, London, catalogue number 2007.64-65, station 143, 05º15.8’N 73º22.8’E- 05º13.7’N 73º23.6’E, 797 m) collected by the John Murray Expedition on 30 March 1934. This was the only record of this species from the Indian Ocean. These specimens appear to have been misplaced (P. Clark, pers. comm.), and we have not been able to locate them for this study. Considering their provenance, it is possible they also belong to C. fasciata n. sp.

Figures

FIGURE 1. Carcinoplax fasciata n. sp., holotype male (25.8 × 19.3 mm) (DABFUK), Kerala, India. Colour in life. A, overall habitus, dorsal view; B, ventral view. Scale bar = 10.0 mm.

FIGURE 2. Carcinoplax fasciata n. sp., holotype male (25.8 × 19.3 mm) (DABFUK), Kerala, India. A, overall habitus; B, left third maxilliped; C, anterior thoracic sternum and pleon; D, posterior thoracic sternum and pleon.

FIGURE 3. Carcinoplax fasciata n. sp., holotype male (25.8 × 19.3 mm) (DABFUK), Kerala, India. A, B, frontal view of cephalothorax; C, outer view of right major chela; D, inner view of right major chela; F, outer view of left minor chela; E, inner view of merus and carpus of right major cheliped; G, left P 3; H, left P 5.

FIGURE 4. Carcinoplax fasciata n. sp., holotype male (25.8 × 19.3 mm) (DABFUK), Kerala, India. Gonopods. A, ventral view of left G 1; B, distal part of left G 1 (ventral view); C, distal part of left G 1 (dorso-mesial view); D, distal part of left G 1 (dorsal view); E, ventral view of left G 2; F, tip of distal segment of G 2. Scales: A, E = 1.0 mm; B – D, F = 0.5 mm.

FIGURE 5. Carcinoplax specularis Rathbun, 1914, holotype male (23.0 × 16.7 mm) (USNM 46164), Luzon, Philippines. A, overall habitus; B, left third maxilliped; C, frontal view of cephalothorax; D, anterior thoracic sternum and pleon.