Hexaplax aurantium, Rahayu & Ng, 2014

Rahayu, Dwi Listyo & Ng, Peter K. L., 2014, New genera and new species of Hexapodidae (Crustacea, Brachyura) from the Indo-West Pacific and east Atlantic, Raffles Bulletin of Zoology 62, pp. 396-483 : 473-474

Hexaplax aurantium , new species

( Figs. 2F , 56C , 57C , 58C , 59D–F , 60B , 61A , 63 , 64 )

Hexaplax megalops – Tesch, 1918: 242. (not Hexaplax megalops Doflein, 1904 )

Material examined. Holotype: male (15.3 × 10.8 mm) ( MNHN- IU-2158 ), CP 3707, 04°59'S 145°50'E, Madang, 460–466 m, Papua New Guinea, coll. BIOPAPUA Expedition, 2 October 2010 . Paratypes: Papua New Guinea: 6 females (12.4 × 8.7 mm – 18.7 × 13.3 mm) (MNHN-IU-2011-2794), station CP 3692, 02°10'S 147°19'E, southeast Manus Island , 408–448 m, coll. BIOPAPUA Expedition, 29 September 2010 ; 2 males (12.0 × 8.6 mm, 12.1 × 8.4 mm), 3 females (11.8 × 8.8 mm – 16.3 × 11.5 mm) ( MNHN- IU-2011-1527 ) , 2 males (14.0 × 9.5 mm, 14.2 × 9.8 mm), 5 females (11.9 × 8.3 mm – 15.2 × 10.7 mm) (MNHN-IU-2011-1066), station CP 3635, 07°29'S 147°33'E, south of Lae, Gulf of Huon , 280–302 m, coll. BIOPAPUA Expedition, 23 August 2010 ; 3 males (13.1 × 9.0 mm – 18.1 × 12.4 mm), 4 females (17.3 × 12.4 mm – 20.7 × 15.0 mm) (MNHN-IU-2011-3519), station CP 3708, 04°58'S 145°50'E, Madang, 502–529 m, coll. BIOPAPUA Expedition, 2 October 2010 ; 2 males (14.6 × 10.0 mm, 16.9 × 11.6 mm), 3 females (13.3 × 9.6 mm – 16.6 × 12.1 mm) ( ZRC 2013.1696 ex MNHN-IU-2158), station CP 3707, 04°59'S 145°50'E, Madang, 460–466 m, coll. BIOPAPUA Expedition, 2 October 2010 ; 1 male (13.8 × 9.6 mm), 2 females (14.6 × 10.4 mm, 14.9 × 10.6 mm) (MNHN-IU-1461), 1 male (13.0 × 8.7 mm) (MNHN-IU-1392), station CP 3669, 04°08'S 151°56'E, north of Rabaul , 382–389 m, coll. BIOPAPUA Expedition, 24 September 2010 ; 2 females (13.9 × 9.4 mm, 16.5 × 11.3 mm) (MNHN-IU-2640), station CP 3691, 02°11'S 147°18'E, southeast of Manus Island , 499–517 m, coll. BIOPAPUA Expedition, 29September 2010 ; 1 female (12.2 × 8.6 mm) (MNHN-IU-2011-1723), station CP 3729, 07°52'S 148°03'E, Mambare Bay , 575–655 m, coll. BIOPAPUA Expedition, 8 October 2010 ; 1 female (9.5 × 6.6 mm) (MNHN-IU-2011-993), station CP 3734, 08°16'S 150°30'E, Lancasey Island , 389 m, coll. BIOPAPUA Expedition, 9 October 2010 ; 1 male (13.6 × 9.6 mm) ( MNHN- IU-2011-987 ), station CP 3655, 02°15'S 150°16'E, west of New Hanover , 402–440 m, coll. BIOPAPUA Expedition, 28 August 2010 ; 1 male (12.3 × 8.6 mm), 3 females (9.6 × 6.9 mm – 14.1 × 9.9 mm) (MNHN-IU-2011-3386), station CP 3646, 06°45'S 147°49'E, Tami Island , 460–485m, coll. BIOPAPUA Expedition, 24 August 2010 ; 3 males (12.1 × 8.5 mm – 14.6 × 10.1 mm), 4 females (10.1 × 7.2 mm – 18.5 × 12.9 mm (MNHN-IU-2011-1704), station CP 3728, 07°52'S 148°01'E, Mambare Bay , 498–501 m, coll. BIOPAPUA Expedition, 8 October 2010 ; 1 female (13.2 × 9.5 mm) ( ZRC 2013 . 1697), CP 3957, 05°05'S 145°51'E, Bismarck Sea, Madang, west of Sek Island , 452–504 m, coll. Expedition PAPUA NUIGINI, 28 November 2012 .

Diagnosis. Carapace subquadrate, about 1.4 times as broad as long, dorsal surface finely granulated; regions indistinct, median H-shaped depression shallow ( Fig. 63 ). Anterolateral margin arcuate; posterolateral corner with small angle over base of posterior pereopods. Front not deflexed ( Fig. 56C ), divided into 2 lobes, not projecting beyond distal edge of orbits. Orbit distinct, transverse; eye movable, large, corneas dilated, pigmented, much wider than peduncle ( Figs. 56C , 61A ). Pterygostomial region with oblique stridulatory ridge consist of long row of 25 short striae, including about 14 shorter, less produced striae adjacent to epistome ( Fig. 60B ); shallow oblique groove above ridge. Third maxillipeds ( Figs. 64A ) relatively broad, not completely covering buccal cavity, with gap when closed; ischium longer than broad, longer than merus, dilated distally, mesial margin rounded; merus squarish, as long as broad; exopod relatively narrow, about 0.3 width of ischium, flagellum well developed. Chelipeds subequal ( Fig. 57C ); major chela with slight gap when fingers closed; with large teeth at cutting edge of dactylus and fixed finger; dactylus, palm and carpus granulated on outer surface; outer surface of dactylus with 2 longitudinal ridges; inner surface with longitudinal ridge consist of oblique striae; fixed finger with 2 longitudinal ridges; lower margin with row small teeth continuing to lower margin of palm; minor chela with gap proximally when fingers closed; ornamentation similar to that of major chela. P2–P4 long, slender ( Fig. 63 ); outer surface granulated; merus of P4 7.6 times as longas broad, upper margin of merus and carpus granulated, shallow longitudinal groove on outer surface of propodus ( Fig. 59D–F ). Male thoracic sternum broad ( Fig. 58C ), surface finely granular; sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 not separated from sternite 4, sternites 4–7 well developed, separated by distinct sutures; sternoabdominal cavity reaching middle of sternite 4, no thoracic sternal groove; sternite 8 not visible. Male abdomen relatively narrow ( Figs. 58C , 64B ); somite 1 hidden under carapace; somite 2 free, somites 3–5 fused with shallow suture visible, lateral margin sinuous; somite 6 wider than long, lateral margin slightly expanded subproximally; telson rounded, about same length as somite 6. G1 long, slender, tapering to pointed tip ( Fig. 64C, D ), unarmed. Female thoracic sternum broad; sternoabdominal cavity reaching middle of sternite 4; female abdomen relatively broad ( Fig. 64E ); somite 1 hidden under carapace; somite 2–6 free; telson rounded, as long as somite 6.

Colour. In life, the carapace is cream-mottled with orange margin, the eye is cream with orange longitudinal stripes on the lateral and mesial margins, and an orange spot under the cornea. T cheliped is white with an orange stripe on the articulation of the dactylus and palm, and distal margins of the carpus and merus of P2−P4 are orangish-white ( Fig. 2F ).

Etymology. From the Latin noun aurantium for citrus; alluding to the orange colour of the species in life.

Remarks. See remarks for H. megalops s. str. for differences with congeners.

Tesch (1918) recorded several specimens of “ Hexaplax megalops ” from Saleyer Island (southern Sulawesi) and north of Bali. On the basis of the adult measurements provided by Tesch (1918: 243), the carapace width to length ratios of these specimens ranged from 1.34 to 1.43, indicating they probably belong to H. aurantium , new species. Hexaplax megalops , which also occurs in New Guinea waters and may be present in Sulawesi and Bali, has a proportionately broader carapace, with a width to length ratio of 1.5.

Type locality. Madang, Papua New Guinea .

Distribution. Papua New Guinea. Deep water, 280− 655 m.

Figures

Fig. 2. Colours in life. A, Mariaplax ourabay, new species, holotype male (7.6 × 5.4 mm) (RUMF-ZC-2114), Oura Bay, Okinawa Island, Japan; B, Mariaplax ourabay, new species, paratype female (9.2 × 7.0 mm) (ZRC 2012.1032), Oura Bay, Okinawa Island, Japan; C, Mariaplax narusei, new species, holotype male (9.6 × 5.8 mm) (RUMF-ZC-2112), Funaura Bay, Iriomote Island, Japan; D, Rayapinus maenosonoi, new species, holotype male (6.6 × 4.9 mm) (RUMF-ZC-2115) Sesoko, Okinawa, Japan; E, Hexaplax megalops Doflein, 1904, male, (13.5 × 9.0 mm) (MNHN-IU-2011-1026), west of New Hanover; F, Hexaplax aurantium, new species, paratype male (12.1 × 8.4 mm) (MNHN-IU-2011-1527), south of Lae, Gulf of Huon; G, Hexaplax saudade, new species, paratype male (16.9 × 9.8 mm) (ZRC 2013.1692), AURORA, 2007, station CP2658, Philippines; H, Hexaplax saudade, new species, male (15.9 × 11.1 mm) (ZRC 2008.1456), Su-Ao fish port, Ilan province, Taiwan.

Fig. 56. Frontal view of cephalothorax. A. Hexaplax megalops Doflein, 1904, holotype male (15.0 × 10.0 mm) (ZMB); B, Hexaplax megalops Doflein, 1904, male (18.7 × 12.1 mm) (MNHN-IU-2011-2251); C. Hexaplax aurantium, new species, holotype male (15.3 × 10.8 mm) (MNHN-IU-2011-2158); D. Hexaplax saudade, new species, holotype male (16.4 × 12.1 mm) (NMCR).

Fig. 57. Chelae. A. Hexaplax megalops Doflein, 1904, male (18.7 × 12.1 mm) (MNHN-IU-2011-2251); B, Hexaplax aurantium, new species, holotype male (15.3 × 10.8 mm) (MNHN-IU-2011-2158); C, Hexaplax aurantium, new species, paratype female (13.2 × 9.5 mm) (ZRC 2013.1696); D, Hexaplax saudade, new species, holotype male (16.4 × 12.1 mm) (NMCR).

Fig. 58. Ventral view of carapace showing abdomen and telson and third maxillipeds. A, Hexaplax megalops Doflein, 1904, holotype male (15.0 × 10.0 mm) (ZMB); B, Hexaplax megalops Doflein, 1904, male (18.7 × 12.1 mm) (MNHN-IU-2011-2251); C, Hexaplax aurantium, new species, holotype male (15.3 × 10.8 mm) (MNHN-IU-2011-2158); D, Hexaplax saudade, new species, paratype male (17.9 × 12.7 mm) (ZRC 2013.1694)

Fig. 59. Right P4, outer surface. A, Hexaplax megalops Doflein, 1904, holotype male (15.0 × 10.0 mm); B, Hexaplax megalops Doflein, 1904, female (17.7 × 12.2 mm) (MNHN-IU-2011-2251); C, Hexaplax megalops Doflein, 1904, male (18.7 × 12.1 mm) (MNHN- IU-2011-2251); D, Hexaplax aurantium, new species, holotype male (15.3 × 10.8 mm)(MNHN-IU-2011-2158); E, Hexaplax aurantium, new species, paratype female (17.6 × 12.4 mm) (MNHN-IU-2011-2158); F, Hexaplax aurantium, new species, paratype female (13.2 × 9.5 mm) (MNHN); G, Hexaplax saudade, new species, holotype male (16.4 × 12.1 mm); H, Hexaplax saudade, new species, paratype female (13.1 × 9.7 mm).

Fig. 60. Pterygostomial region showing row of stridulatory striae. A, Hexaplax megalops Doflein, 1904, male (18.7 × 12.1 mm) (MNHN- IU-2011-2251); B, Hexaplax aurantium, new species, holotype male (15.3 × 10.8 mm)(MNHN-IU-2011-2158); C, Hexaplax saudade, new species, holotype male (16.4 × 12.1 mm) (NMCR).

Fig. 61. A, Hexaplax aurantium, new species, paratype female (13.2 × 9.5 mm); B, Hexaplax saudade, new species, paratype male (17.9 × 12.7 mm) (ZRC 2013.1694); C, Hexaplax megalops Doflein, 1904, male (18.7 × 12.1 mm) (MNHN-IU-2011-2251). A, front showing eyes in orbit; B, anteroventral view of cephalothorax showing abdomen and telson, third maxillipeds and stridulatory ridge on pterygostomial regions; C, inner surface of palm.

Fig. 63. Hexaplax aurantium, new species. Overall view of carapace, chelipeds and P2–P4. A, holotype male (15.3 × 10.8 mm) (MNHN- IU-2011-2158); B, paratype female (17.6 × 12.4 mm) (ZRC 2013.1696, ex MNHN-IU-2011-2158); C, paratype female (13.2 × 9.5 mm) (ZRC 2013.1697).

Fig. 64. Hexaplax aurantium, new species. A–D, holotype male (15.3 × 10.8 mm) (MNHN-IU-2011-2158); E, paratype female (13.2 × 9.5 mm). A, left third maxilliped; B, male abdomen and telson; C, D, G1; E, female abdomen and telson. Scale bars = 1.0 mm.