Carcinoplax abyssicola ( Miers, 1885 )

Ng, Peter K. L. & Castro, Peter, 2020, A revision of Carcinoplax abyssicola (Miers, 1885) and seven related species of Carcinoplax H. Milne Edwards, 1852, with the description of two new species and an updated key to the genus (Crustacea, Decapoda, Brachyura, Goneplacidae), Zoosystema 42 (17), pp. 239-284 : 243-251

Carcinoplax abyssicola ( Miers, 1885)

( Figs 1 A-D; 2 A-H; 3 A-I; 4 A-H; 5 A-H; 23 A-D, E-H; 26 A-F)

Pseudorhombila (Pilumnoplax) abyssicola Miers, 1885: 588 [ Fiji].

Pilumnoplax abyssicola Miers, 1886 : xxiv, xl, xlviii, 226, 227 [in list], 228, pl. 19, figs 2, 2a, 2b [ Fiji]. — Tesch 1918: 155 [in list], 156 [in key], 156 [ Indonesia]. — Serène 1968: 90 [in list]. — Guinot 1969: 526; 1971: 1081 [in list]. — Serène & Lohavanijaya 1973: 62 [in list], 65 [in key].

Not Pilumnoplax abyssicola – Whitelegge 1900: 158 (= Pycnoplax meridionalis (Rathbun, 1923)) .

Neopilumnoplax abyssicola – Serène 1968: 90 [in list].

Carcinoplax abyssicola – Guinot 1969: 526; 1989: 305, fig. 38; pl. 9, figs A-C [holotype] [ Fiji]. — Castro 2007: 623 [in list]. 627 [in key], 628 [holotype] [ Fiji]. — Ng et al. 2008: 80 [in list].

Carcinoplax specularis [part] – Castro 2007: 640 [ Indonesia, New Guinea, Solomon Islands, Vanuatu, New Caledonia, Fiji, Tonga].

TYPE MATERIAL. — Holotype. Fiji. ♂, 8.2 × 10.0 mm ( Castro 2007), Challenger ; stn 173; NHM 84.31 .

TYPE LOCALITY. — Fiji, Challenger; stn 173; 576 m depth.

MATERIAL EXAMINED. — Indonesia • 1 ♀, 11.2 × 15.2 mm; Kai Is.; KARUBAR; stn CP59; 08°20’S, 132°11’E; 399-405 m depth; 31.X.1991; MNHN-IU-2016-100 (= MNHN-B29387 ) • 1 ♀, 19.3 × 24.5 mm; KARUBAR; stn CP63; 08°00’S, 132°58’E; 214-215 m depth; 1.XI.1991; MNHN-IU- 2016-99 (= MNHN-B29380 ) • 1 ♀, 12.4 × 17.6 mm; Java; E. Sunda Strait; SJADES; stn CP7; 05°44.678’S, 104°51.151’E; 379-409 m depth; 25.III.2018; ZRC 2018.1414 • 4 ♀, 1 ovigerous ♀, 1♂; same data as ZRC 2019.0568 • 1 ♀, 13.9 × 19.9 mm, 1 ♀, 14.8 × 20.0 mm, 1 ♂, 12.8 × 19.1 mm, 1 ♂, 13.6 × 18.4 mm; Java; E. Sunda Strait; SJADES; stn CP8; 05°45.126’S, 104°51.080’E; 425-442 m depth; 25.III.2018; ZRC 2018.1415 • 5 ♀, 7.6 × 10.1 mm to 14.5 × 21.2 mm; same data as ZRC 2019.0569 • 5 ♀; same data as ZRC 2019.0569 • 1♂, 13.0 × 19.4 mm; SJADES; stn CP10; Java; E. Sunda Strait; 05°45.399’S, 104°56.098’E; 429-446 m depth; 25.III.2018; ZRC 2018.1416 • 1 ♂, 2♀, 10.0 × 13.8 mm, 11.9 × 16.1 mm, 1 ♂, 13.9 × 20.3 mm; SJADES; stn CP39; E. Indian Ocean; 08°15.885’S, 109°10.163’E; 528-637 m depth; 30.III.2018; ZRC 2018.1418 .

Papua New Guinea • 1 ♂, 14.3 × 19.1 mm; BIOPAPUA; stn CP3570; 1.X.2010; 497-500 m depth; ZRC 2019.1029 ; ex MNHN- IU-2011-1469 • 1 ♂, 11.8 × 16.5 mm; BIOPAPUA; stn CP3740; 556-645 m depth; 10.X.2010; MNHN-IU-2011-2471 • 1 ♂, 13.2 × 16.4 mm; BIOPAPUA; stn CP3742; 448-470 m depth; 10.X.2010; ZRC 2019.1028 ; ex MNHN-IU-2011-2001 • 1 ♀, 13.9 × 11.0 mm; PAPUA NIUGNI; stn CP3970; 04°39’S, 145°52’E; 573 m depth; 4.12.2012; MNHN-IU-2013-9399 • 1 ♀, 11.0 × 11.7 mm; PAPUA NIUGNI; stn CP4033; 04°52’S, 145°53’E; 780 m depth; 16.12.2012; MNHN-IU-2013-9402 • 1 ♀, 11.8 × 16.7 mm; PAPUA NIUGNI; stn CP4042; 03°53’S, 144°40’E; 495-693 m depth; 18.XII.2012; MNHN-IU-2013-9391 • 1 ♂, 8.7 × 11.0 mm; PAPUA NIUGNI; stn CP4048; 03°20’S, 143°28’E; 325-345 m depth; 19.XII.2012; MNHN-IU-2013-9405 • 1 ♂, 6.0 × 7.4 mm; same data as MNHN- IU-2013-9405; MNHN-IU-2013-15592 • 1 ♂, 8.1 × 9.9 mm; same data as MNHN-IU-2013-9405; MNHN-IU-2013-9393 .

Solomon Islands • 1 ♀, 11.7 × 15.9 mm; SALOMON 1; stn CP1747; 09°21.8’S, 159°58.7’E; 364-402 m depth; 25.IX.2001; MNHN- IU-2016-129 (= MNHN-B29394 ) • 1 ♀, 11.1 × 16.1 mm; SALO- MON 1; stn CP1748; 09°20.4’S, 159°58.2’E; 509-522 m depth; 25.IX.2001; MNHN-IU-2016-128 (= MNHN-B29395 ) • 1 ♂, 5.8 × 7.5 mm; SALOMON 1; stn DW1768; 08°21.4’S, 160°41.8’E; 194-286 m depth; 28.IX.2001; MNHN-IU-2016-127 (= MNHN- 29393 ) • 2 ♀, 6.2 × 7.6 mm; 12.9 × 16.5 mm; SALOMON 1; stn DW1808; 09°45.5’S, 160°52.5’E; 611-636 m depth; 2.X.2001; MNHN-IU-2016-130 (= MNHN-B29396 ) • 1 ♀, 12.3 × 18.8 mm; SALOMON 1; stn DW1851; 10°27.6’S, 162°00’E; 297-350 m depth; 6.X.2001; MNHN-IU-2016-131 (= MNHN-B29397 ) • 1 ♀, 10.5 × 13.7 mm; SALOMON 1; stn CP2288; 08°36.3’S, 157°26.5’E; 509-520 m depth; 7.XI.2004; MNHN-IU-2016-133 (= MNHN-B30095 ) . • 2 ♀, 10.9 × 14.0 mm; 13.8 × 19.2 mm; SALOMON 2; stn CP2195; 08°25.5’S, 159°26.4’E; 543-593 m depth; 24.X.2004; MNHN-IU-2016-136 (= MNHN-B30111 ) • 1 ovigerous ♀, 13.5 × 18.8 mm; SALOMON 2; stn 2212; 07°37.8’S, 157°41.7’E; 400-475 m depth; 26.X.2004; MNHN-IU-2016-134 (= MNHN-B30114 ) • 1 ♂; SALOMON 2; stn CP2213; 07°38.7’S, 157°42.9’E; 495-650 m depth; 26.X.2004; MNHN-IU-2016-138 (= MNHN-B30097 ) • 1 ♀, 2 ♂; SALOMON 2; stn CP2246; 07°42.6’S, 156°24.6’E; 664-682 m depth; 1.X.2004; MNHN-IU-2016-132 (= MNHN-B30109 ) • 1♂, 10.8 × 14.9 mm; SALOMON 2; stn CP2262; 07°56.4’S, 156°51.2’E; 460-487 m depth; 3.X.2004; MNHN-IU-2016-137 (= MNHN-B30112 ) • 1 juvenile, 6.7 × 8.3 mm; SALOMON 2; stn CP2287; 08°40.8’S, 157°24.6’E; 253-255 m depth; 6.XI.2004; MNHN-IU-2016-135 (= MNHN- B30089) • 1 ♀, cl 13.4 mm; carapace damaged; Malaita; SALOMON BOA 3; stn CP2787; 08°31’S, 160°39’E; NW 570-885 m depth; 14.IX.2007; MNHN-IU-2010-5567 • 1 ♂, 8.3 × 9.9 mm; same data as MNHN-IU-2010-5567; MNHN-IU-2010-5568 .

Vanuatu • 1 ♀, 11.9 × 16.2 mm, 2 ♂, 9.9 × 14.1 mm, 14.5 × 19.8 mm; BOA0; stn CP2304; 16°35’S, 167°59’E, 564-582 m depth; 14.XI.2004; MNHN-IU-2016-118 • 1 ovigerous ♀, 12.8 × 17.5 mm; BOA0 ; stn CP2313; 15°04’S, 166°55’E; 421-482 m depth; 16.XI.2004; MNHN-IU-2016-116) • 1 ♂, 10.7 × 14.0 mm; BOA0; stn CP2330; 295-890 m depth; 18.II.2004; MNHN- IU-2016-117 ) • 1 ♀, 11.9 × 14.8 mm; BOA1 ; stn CP2457, 16°16’S, 167°19’E; 630-690 m depth; 6.XII.2005; MNHN-IU-2016-115 • 2 ♀, 9.7 × 12.9 mm, 10.4 × 14.6 mm; SANTO 2006; stn AT9; W. Malo I.; 15°41.5’S, 167°01.3’E, 481 m depth; 17.IX.2006; ZRC 2008.0970 • 1 ♂, 8.0 × 10.6 mm; SANTO 2006; stn AT19; W Malo I.; 15°41’S, 167°01’E; 503-600 m depth; 21.IX.2006; ZRC 2018.1419 • 1 juvenile female; no data; ZRC 2009.0994 .

New Caledonia. 3 ♂; SMIB 6; stn DW212; 19°05.6’S, 163°30.2’E; 220-225 m depth; 2.III.1990; MNHN-IU-2016-120 (= MNHN- B29818) • 1 ♂, 13.0 × 17.6 mm; BATHUS 4; stn CP910; 18°59.32’S, 163°08.47’E; 560-608 m depth; 5.VIII.1994; MNHN-IU-2016-111 (= MNHN-B29417 ) • 2♂; BATHUS 4; stn CP911; 18°57.80’S, 163°08.47’E; 566- 558 m depth; 5.VIII.1994; MNHN-IU-2016-112 (= MNHN-B29420 ) • 1 ♂, 6.0 × 7.3 mm; EXBODI: stn CP3788; 22°13’S, 167°07’E; 264-273 m depth; 3.IX.2011; MNHN- IU-2011-8816 .

Fiji • 3 ♀, largest 11.2 × 15.6 mm; MUSORSTOM 10; stn DW1330; 17°09.5’S, 177°56.3’E; 567-699 m depth; 8.VIII.1998; MNHN- IU-2014-11513 (= MNHN-B29504 ) • 3 ♀, 1 ♂, 10.5 × 15.3 mm; BORDAU 1; stn DW1393; 16°45’S, 179°59’E; 426-487 m depth; 23.II.1999; MNHN-IU-2014-11531 (= MNHN-B29505 ) • 1 juve- nile ♀, 7 ♀, largest 11.7 × 16.0 mm, 2 ♂, larger one 11.0 × 15.5 mm; BORDAU 1; stn DW1395; 16°45’S, 179°59’E; 423-500 m depth; 23.II.1999; MNHN-IU-2014-11529 (= MNHN-B29505 ) • 1 ♀, 2 ♂; ZRC 2019.1030 ; same data as MNHN-IU-2014-11529 • 1 ♂, cl 13.4 mm, carapace damaged; BORDAU 1; stn CP1401; 16°35’S, 179°41’E; 600-648 m depth; 25.II.1999; MNHN-IU-2014-11532 (= MNHN-B29506 ) • 1 ♂, 13.3 × 17.8 mm; BORDAU 1; stn CP1407; 16°40’S, 179°39’E, 499-527 m depth; 25.II.1999; MNHN- IU-2014-11533 (= MNHN-B29507 ) • 9 ♀, largest 11.1 × 15.0 mm, 4 ♂, largest 12.4 × 17.6 mm; BORDAU 1; stn DW1447; 16°45’S, 179°59’E; 420-513 m depth; 4.III.1999; MNHN-IU-2014-11530 (= MNHN-B29503 ) • 2 ♀, 2 ♂; ZRC 2019.1027 ; same data as MNHN-IU-2014-11530 • 1 ♀; BORDAU 1; stn CP1448; 16°45’S, 179°59’E; 410-500 m depth; 4.III.1999; MNHN-IU-2014-11534 (= MNHN-B29508 ) • 2 ♀, 1 ♂; BORDAU 1; stn DW1451; 16°45’S, 179°59’E; 400-460 m depth; 4.III.1999; MNHN-IU-2014-11535 (= MNHN-B29509 ) • 1 juvenile ♀, 1 ♀, cl 9.4 mm, carapace damaged; BORDAU 1; stn DW1453; 16°45’S, 179°59’E; 414- 510 m depth; 4.III.1999; MNHN-IU-2014-11536 (= MNHN- B29510) • 1 ♀, 7.2 × 9.9 mm; BORDAU 1; stn DW1463; 18°10’S, 178°44’W; 300-400 m depth; 6.III.1999; MNHN-IU-2014-7671 (= MNHN-B29511 ) • 1 ♂; BORDAU 1; stn DW1491; 18°50’S, 178°52’W; 777-787 m depth; 11.III.1999; MNHN-IU-2014-7697 (= MNHN-B29511 ) .

Tonga • 1 juvenile ♀; BORDAU 2; stn CP1530; 21°12’S, 174°58’W; 802-803 m depth; 3.VI.2000; MNHN-IU-2014-11538 (= MNHN- B29555) • 3 ♀; BORDAU 2; stn CP1539; 21°37’S, 175°19’W; 558-586 m depth; 4.VI.2000; MNHN-IU-2014-11539 (= MNHN- B29558) • 1 ♀, 1 ♂; BORDAU 2; stn DW1553; 20°42’S, 174°54’W; 650-676 m depth; 6.VI.2000; MNHN-IU-2014-11544 (= MNHN- B29566) • 1 ♀; BORDAU 2; stn CP1556; 20°11’S, 174°45’W; 589-591 m depth; 7.VI.2000; MNHN-IU-2014-11541 (= MNHN- B29560) • 1 juvenile ♀; BORDAU 2; stn CP1557; 20°10’S, 174°42’W; 578 m depth; 7.VI.2000; MNHN-IU-2014-11543 (= MNHN-B29563 ) • 8 ovigerous ♀, 4 ♀, 1 ♂; BORDAU 2; stn CP1568; 21°02’S, 175°19’W; 431 m depth; 10.VI.2000; MNHN- 2014-11537 (= MNHN-B29309 ) • 1 ♀, 1 ♂; ZRC 2019.1031 ; same data as MNHN-2014-11537; 2 ovigerous ♀, largest 13.3 × 18.0 mm, 8 ovigerous ♀, 5 ♀, 2 ♂; same data as MNHN- 2014- 11537; MNHN-2014-11537 (= MNHN-B29309 ) • 2 ovigerous ♀; BORDAU 2; stn CP1620; 24°18’S, 176°20’W; 572 m depth; 18.VI.2000; MNHN-IU-2014-11540 (= MNHN-B29559 ) • 1 ju- venile ♀; BORDAU 2; stn CP1641; 21°09’S, 175°22’W; 395 m depth; 21.VI.2000; MNHN-IU-2014-11542 (= MNHN-B29561 ) .

RE- DESCRIPTION

Carapace ( Figs 1A, D ; 2A, B, I ; 3A, B ; 4A, B ; 5A, B ; 26 A-F) Quadrate, slightly wider than long (1.2 × as wide as long in holotype; Castro 2007), anterolateral borders arched; slightly convex, mostly smooth, rarely granular in large specimens, marked by slight transverse elevations in branchial regions. Front ( Figs 3C, D ; 4C, D ; 5C ) lamellar, straight, margin not marked by median notch; notch between front, inner edge of supraorbital border. Supraorbital borders sinuous, margins smooth; suborbital borders with short, rounded inner tooth, reduced in some specimens. Outer orbital angles truncated when seen dorsally; first anterolateral teeth rounded but sometimes acute, second curved, acute-tipped. Posterolateral borders arched. Subhepatic, pterygostomial regions, pterygostomial crest, pterygostomial lobe, merus, ischium of third maxilliped endopod with short, small granules. Posterior margin of epistome ( Figs 2C ; 3C, D ; 4C, D ; 5C ) straight, slight median projection in some specimens; u- or v-shaped notch on each lateral margin.

Chelipeds ( Figs 1A, C ; 2A, F, H ; 3A, F, I ; 4A, F, H ; 5A, H ; 26 A-F) and ambulatory legs ( Figs 1A, D ; 2A ; 3A ; 4A ; 5A ; 26 A-F)

Chelipeds (P1) nearly equal in females and males; fingers slender, about as long or slightly shorter as propodus, with cutting edges, broadly blunt teeth; nearly all distal portion of fingers dark brown in males, half to 3/ 4 in females ( Figs 1A, C ; 2A, F, H ; 3A, F, I ; 4A, H ; 5A, H ; 26 A-F). “Window” (see discussion of C. specularis below) observed on outer surface of cheliped propodi in several males (e.g. MNHN- IU-2014-11529, 11.0 × 15.5 mm [ Fig. 3I ] and MNHN- IU-2016-127, 5.8 × 7.5 mm). Inner, outer (dorsal), distal margin of cheliped carpus with short, triangular to acute tooth ( Figs 1A, C ; 2F ; 3F ; 4F ; 5E ). P2-P5 ( Figs 1A, D ; 2A ; 3A ; 4A ; 5A ; 26 A-F) slender, proportionally long, smooth; many short, simple setae along inner, outer margins of P5 propodus, dactylus, outer margin of P5 carpus; P5 dactylus long, slender, smooth.

Sternum, male pleon ( Figs 2D ; 3H ; 4G ), and male gonopods ( Fig. 23 A-C, E-G)

Tomentum on sternum and pleon of large individuals of both sexes. Male pleon ( Figs 2D ; 3H ; 4G ) proportionally wide, with 6 freely-movable somites plus telson; telson slightly wider than long, somite 3 covering space between P5 coxae. Somites 1, 2 slightly narrower than somite 3, thoracic sternite 8 not visible. G1 ( Fig. 23 A-C, E-G) straight, short, obtuse to slightly laterally pointed tip; dorsal surface with numerous minute spinules that nearly reach tip. G2 ( Fig. 23D, H ) slender, slightly longer than G1, slightly curved flagellum, tip with spinule at each side.

Female pleon ( Fig. 5F ) and vulva ( Fig. 5G )

Female pleon ( Fig. 5F ) wide; telson slightly wider than long. Somites 1, 2 covering space between P5 coxae, thoracic sternite 8 not visible.Vulva of mature females ( Fig.5G ) extending from edge of suture 5/6 to suture 6/7; membrane covering aperture leaving space open along pointed anterior margin.

COLOUR IN LIFE. — Carapace and chelipeds light to bright orange; legs white with broad orange band across middle ( Fig. 26 A-F).

GEOGRAPHICAL DISTRIBUTION. — Indonesia (Kai Is and southern Java), Papua New Guinea, Solomon Islands, Vanuatu, New Caledonia, Fiji, and Tonga.

DEPTH. — Present in samples collected at depths of 194- 890 m.

REMARKS

The taxonomy of C. abyssicola , C. longipes , and C. verdensis has been confused mainly because of a shortage of specimens, as well as having type specimens that are small or females. It has been made more difficult because these species sometimes overlap in distribution, with C. abyssicola and C. longipes now known to co-occur in southern Java.

Carcinoplax abyssicola has been a problematic species because it was described from only one small male (8.2 × 10.0 mm, NHM 84.31), and its affinities with allied taxa have been far from clear. Guinot (1989) and Castro (2007) examined the holotype male and the present study confirms the specimens from Fiji, Papua New Guinea, Solomon Islands, Vanuatu, New Caledonia, Tonga and Indonesia (Kai Is and southern Java) are conspecific with the type. The anterolateral armature varies to some degree; the holotype has a small first tooth on the right side while that on the left side is missing ( Fig. 1B ). A male (10.5 × 15.3 mm, MNHN-IU-2014-11531) also has an acute right tooth but an obtuse left tooth ( Fig. 2I ). The holotype specimen no longer has the male pleon and the gonopods are not in the bottle. The G1 and G2 of the holotype, however, were sketched by the second author in 2004. Their morphology agrees with the gonopods drawn here ( Fig. 23 A-C, E-G), except that the tip of the G1 appears slightly longer. It, however, falls within the variation observed in the species.

The description by Miers (1886: 228) agrees with the material at hand but the diagnostic details in the description are scant. We are therefore re-describing the species in order to include a good number of diagnostic characters not included in the original description. No mention was made of the notch at the lateral borders of the front as well as details on the morphology of the epistome and the gonopods. Miers’ figures clearly show the small granules along the anterior portion of the ventral surface of the carapace, which are diagnostic for the species ( Miers 1886: pl. 19, fig. 2a; Fig. 1B, C ), and the fingers of the male holotype were black along their distal twothirds ( Miers 1886: pl. 19, fig. 2b; Fig. 1A, C ) (now faded in the type specimen; Fig. 1G, H ).

With only one specimen at that time, Guinot (1989) accepted the validity of C. abyssicola and indicated that it was close to C. longipes . Castro (2007) commented on the similarities between the holotype of C. abyssicola and specimens of C. specularis s.l., a species in which he included two species now being resurrected. He found that the main difference between the two species was the truncated and posteriorly inclined outer orbital angles of the holotype of C. abyssicola , a condition that is visible in the illustrations of the holotype by Guinot (1989: fig. 38; pl. 9, figs A, B).

Although we are now able to separate C. specularis s. str. (and the allied C. adelphia n. sp.) from the other species previously included under it (see Remarks for this species), the taxonomic history of C. abyssicola , C. longipes , and C. verdensis is confusing and is best discussed together here.

The presence of a good series of fresh specimens of C. abyssicola and C. longipes in the deep waters of southern Java is significant as it allows us to compare them directly. They are most easily distinguished by the proportions of their legs, which in C. longipes are distinctly longer ( Figs 6A ; 7A ; 8A ; 9A ; 27 A-C), especially the meri. The ambulatory meri of C. abyssicola are relatively shorter and stouter ( Figs 1A, E ; 2A ; 3A ; 4A ; 5A ; 26 A-F). Another obvious difference, which can vary occasionally, is the armature of the anterolateral margin (not including the external orbital tooth). The anterolateral teeth of C. abyssicola , especially the first one, are more obtusely triangular in adults ( Figs 1E ; 2B, I ; 3B ; 4B ; 5B ). In C. longipes , the teeth are acutely triangular, appearing almost spiniform, and are spaced further apart as a result ( Figs 6B ; 7B ; 8B ; 9B ). The structure of the posterior margin of the epistome is also useful to separate the two species in most cases; in C. abyssicola , the median truncated lobe is separated from the lateral margins by a relatively shallower and narrower cleft ( Figs 2C ; 3D ; 4F ; 5C ) but this cleft is deeper and wider in C. longipes ( Figs 5C ; 6C ; 7D ; 8D ). The structures of their G1 are superficially similar but the general structure is proportionately shorter and more slender, especially on the basal part ( Fig. 23A, E ) in C. abyssicola , whereas the G1 is more elongated and the basal part is relatively broader and more truncated in C. longipes ( Fig. 23I ).

The two species differ in their colour in life. Carcinoplax abyssicola is a distinct orange ( Fig. 26 A-F), with larger specimens dull or dark orange. The legs are white with a broad orange band across middle portions. In contrast, the overall colour in C. longipes is a faded yellowish-orange with the legs more uniformly coloured ( Fig. 27 A-C).

Carcinoplax abyssicola and C. longipes are both superficially similar to C. verdensis in the shape of their carapaces and the relatively more elongated legs, but C. verdensis can usually be distinguished by several clear features. The inner distal tooth of the carpus of the cheliped in C. verdensis is usually elongated, with the distal half sharply tapering to an acute spine in both sexes and usually even in subadults ( Figs 14F ; 15E ). The inner distal tooth of the carpal spine is always more obtuse and the distal part is never spiniform in C. abyssicola ( Figs 2E ; 3G ; 4F , 5E ) and C. longipes ( Figs 6E ; 7F ; 8F ; 9E ). The carpal spine of Miers’ drawing of the holotype of C. abyssicola is nevertheless spiniform ( Fig. 1C ), but obtuse in Guinot’s photograph of the holotype ( Fig. 1E ). Some specimens of C. verdensis from the Philippine and South China seas, however, have relatively less elongated carpal spines ( Fig. 13F ); so this character is not always reliable. The ambulatory meri of C. verdensis is usually elongated and slender ( Figs 13A ; 14A ; 15A ) like in C. longipes ( Figs 6A ; 7A ; 8A ), but the ambulatory merus appears relatively shorter in a few specimens ( Fig. 9A ), although it is still longer than those of adult C. abyssicola ( Figs 1A, E ; 2A ; 3A ; 4A ; 5A ). The structure of the posterior margin of the epistome of C. verdensis resembles that of C. abyssicola , with the truncated median lobe separated from the lateral margins by a relatively deep cleft ( Figs 2C, D ; 4D ; 5C for C. abyssicola ; Figs 6C ; 7D ; 8D ; 9C for C. longipes ). Carcinoplax verdensis more closely resembles C. longipes in the shape of their anterolateral teeth, with the spines typically more acute and spiniform ( Figs 6B ; 7B ; 8B ; 9B for C. longipes ; Figs 13B ; 14B ; 15B for C. verdensis ). There are, however, several specimens that have more obtuse teeth ( Fig. 13B ), demonstrating that the shape of anterolateral teeth is not always a reliable character among these and other species of Carcinoplax .

Two characters, however, seem constant for C. verdensis and support our view that this is a distinct species. The fingers of the chelipeds in adult C. verdensis of both sexes are dark brown or almost black only along the distal two-thirds to half of the fingers ( Figs 13I, J ; 14H ; 15A ); whereas in C. abyssicola and C. longipes , almost the entire length of the fingers in adults is pigmented ( Figs 1C ; 2F, H ; 3F, I ; 4H ; 5H for C. abyssicola ; Figs 6A ; 7A ; 8H ; 9H for C. longipes ). While the G1 of C. verdensis is similar to that of C. abyssicola , being relatively shorter and less broad basally, the distal part in C. verdensis is always directed obliquely outwards ( Fig. 24 A-C), whereas the distal part is more truncated and the tip is directed laterally in C. abyssicola ( Fig. 23 A-C, E-G).

Additional support on the distinct nature of C. abyssicola has been provided by preliminary data based on the barcode region of the cytochrome oxidase I (COI) gene (L. Corbari, unpublished data) as well as C. abyssicola and the remaining species treated here (L. M. Tsang, unpublished data).

On the basis of the figures of the specimens, and in particular the structures of the G1, it is clear that the material referred to as ‘ Carcinoplax aff. longipes ’ by Guinot (1989) ( Fig. 24E, G ) belongs to C. verdensis as presently defined.

The known geographical distributions of the four species being discussed are relatively distinct. Carcinoplax abyssicola so far is known from the western Pacific, from southeastern Moluccas and southern Java in Indonesia to Tonga (see above) as well as in the easternmost part of the Indian Ocean. Carcinoplax longipes is known only from the Indian Ocean, although it occurs in the same area as C. abyssicola in southern Java. The two species, however, seem to have different habitats and were only collected together from one station (out of 10 stations) in Java. Carcinoplax verdensis is known for certain only from Japan, Taiwan, Philippines, and South China Sea (see below). Carcinoplax fasciata is so far known from the Arabian Sea off the coast of Kerala, India. Carcinoplax abyssicola and the species treated here so far extend east as far as Tonga. The only species of Carcinoplax east of Tonga are two small-size species, C. velutina Castro, 2007 and C. uncinata Castro, 2009 both known from French Polynesia. Carcinoplax velutina is also found in Vanuatu, New Caledonia, and Fiji ( Castro 2007); C. uncinata in New Caledonia and Solomon Islands ( Castro 2009). Carcinoplax uncinata is herein recorded from French Polynesia for the first time (male 8.8 × 11.4 mm, TARASOC; stn CP3376, Tuamotu Archipelago, 15°41’S, 146°54’W, 646- 737 m depth; 10.V.2009, MNHN-IU-2011-5233).

The depth distribution is similar in all three species. Specimens of C. abyssicola and C. longipes were taken at maximum depths of 890 m and 870 m, respectively, but one specimen of C. verdensis was recorded at 2149 m, which is likely to be in error.

Individuals of C. abyssicola and C. verdensis appear to be larger in size (largest specimens measured reaching 19.3 mm CL and 19.2 mm CL, respectively) than those of C. longipes (largest specimen measured 10.8 mm CL). Of the six species being treated here, C. polita is characterised by having the largest measured individuals, with one specimen 25.9 mm CL.

Specimens collected by the Siboga Expedition from Indonesia and identified as C. abyssicola by Tesch (1918) could not be found in the ZMA, where all other Siboga goneplacids were originally deposited. This record is provisionally recognised as correct as the species is known from that area.

Guinot (1989: 307) commented that in the form of the carapace and anterolateral teeth, C. abyssicola was closest to C. verdensis , but differed in having the teeth more spiniform and the chelae being short and globose. While this difference is usually valid for the structure of the anterolateral teeth, the form of the chela varies with size and sex and it is not a reliable character. As discussed earlier, the two species, however, differ in other characters.

Figures

FIG. 1. — Carcinoplax abyssicola (Miers,1885),holotype ♂ (8.2 × 10.0 mm) (NHM 84.31),Fiji:A, overall habitus;B, dorsal view of carapace;C, frontal view of cepha- lothorax; D, left third maxilliped; E, thoracic sternum and third maxillipeds; F, dorsal view of left cheliped; G, outer view of right chela; H, outer view of left chela.

FIG. 2. — Carcinoplax abyssicola (Miers, 1885): A-H, ♂ (8.0 × 10.4 mm) (MNHN-IU-2014-11535), Fiji; I, ♂ (10.5 × 15.3 mm) (MNHN-IU-2014-11531), Fiji; A, overall habitus; B, I, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, dorsal view of left cheliped; F, dorsal view of right cheliped; G, thoracic sternum and pleon; H, outer view of chelae.

FIG. 3. — Carcinoplax abyssicola (Miers, 1885), ♂ (11.0 × 15.5 mm) (MNHN-IU-2014-11529), Fiji: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, posterior margin of epistome; E, left third maxilliped; F, dorsal view of left cheliped; G, dorsal view of right cheliped; H, thoracic sternum and pleon; I, outer view of chelae.

FIG. 4. — Carcinoplax abyssicola (Miers, 1885), ♂ (13.6 × 18.4 mm) (ZRC 2018.1415), Indonesia: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, posterior margin of epistome; E, left third maxilliped; F, dorsal view of carpus of right cheliped; G, thoracic sternum and pleon; H, outer view of chelae.

FIG. 5. — Carcinoplax abyssicola (Miers, 1885), ♀ (14.8 × 20.0 mm) (ZRC 2018.1415), Indonesia: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, dorsal view of carpus of right cheliped; F, thoracic sternum and pleon; G, sternopleonal cavity and vulvae; H, outer view of chelae.

FIG. 23. — Gonopods: A-D, Carcinoplax abyssicola (Miers, 1885), ♂ (8.0 × 10.4 mm) (MNHN-IU-2014-11535), Fiji; E-H, C. abyssicola, ♂ (11.0 × 15.5 mm) (MNHN-IU-2014-11529), Fiji; I-L, C. longipes (Wood-Mason, 1891), ♂ (9.9 × 13.9 mm) (ZRC 2018.1424), Java. A, E, I, left G1 (ventral view); B, F, J, distal part of left G1 (ventral view); C, G, K, distal part of left G1 (dorsal view); D, H, right G2 (left G2 damaged); L, left G2. Scale bars: A, D, E, H, I, L, 1.0 mm; B, C, F, G, J, K, 0.2 mm.

FIG. 26. — Colour in life, Carcinoplax abyssicola (Miers, 1885). A, ♀ (10.4 × 14.6 mm) (ZRC 2008.0970),Vanuatu; B, ♂ (8.0 × 10.6 mm) (ZRC 2018.1419),Vanuatu; C, ♀ (12.4 × 17.6 mm) (ZRC 2018.1414),Java; D, ♂ (13.0 × 19.4 mm) (ZRC 2018.1416), Java;E, ♂ (12.8 × 19.1 mm) (ZRC 2018.1415),Java; F, ♀ (14.8 × 20.0 mm) (ZRC 2018.1415), Java. Photographs: SJADES.

FIG. 6. — Carcinoplax longipes (Wood-Mason, 1891), ♂ (8.5 × 11.4 mm) (USNM 46291), India: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, dorsal view of carpus of right cheliped; F, thoracic sternum and pleon; G, outer view of chelae.

FIG. 7. — Carcinoplax longipes (Wood-Mason, 1891), ♀ (11.9 × 15.1 mm) (USNM 46291), India: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, posterior margin of epistome; E, left third maxilliped;F, dorsal view of carpus of right cheliped;G, thoracic sternum and pleon;H, sternopleonal cavity and vulvae; I, outer view of chelae.

FIG. 8. — Carcinoplax longipes (Wood-Mason, 1891) ♂ (9.9 × 13.9 mm) (ZRC 2018.1424), Indonesia: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, posterior margin of epistome;E, left third maxilliped; F, dorsal view of carpus of right cheliped; G, thoracic sternum and pleon; H, outer view of chelae.

FIG. 9. — Carcinoplax longipes (Wood-Mason,1891): A-E, G, H, ovigerous ♀ (10.8 × 14.3 mm) (ZRC 2018.1424), Indonesia; F, ♀ (9.9 × 12.9 mm) (ZRC 2018.1424), Indonesia. A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, right third maxilliped; E, dorsal view of carpus of right cheliped; F, thoracic sternum and pleon; G, sternopleonal cavity and vulvae; H, outer view of chelae.

FIG. 27. — Colour in life: A, Carcinoplax longipes (Wood-Mason, 1891), ♂ (9.0 × 12.4 mm) (ZRC 2018.1422), Java; B, C. longipes, ♂ (10.8 × 14.4 mm) (ZRC 2018.1427), Java; C, C. longipes, ovigerous ♀ (10.8 × 14.3 mm) (ZRC 2018.1420), Java; D, C. specularis Rathbun, 1914, ♂ (18.4 × 25.8 mm) (ZRC 2001.0134), Taiwan; E, C. adelphia n. sp., paratype ♂ (15.7 × 21.2 mm) (ZRC 2009.0922), Vanuatu; F, C. adelphia n. sp., paratype ♀ (16.9 × 22.4 mm) (ZRC 2009.0922(, Vanuatu; G, C. polita Guinot, 1989, ♀ (12.8 × 17.8 mm) (ZRC 2006.0176), Philippines; H, C. polita, ♂ (6.5 × 7.9 mm) (ZRC 2018.1417), Java. Photographs: A-C, SJADES; D, P.-H. Ho; E-H, T.-Y. Chan.

FIG. 14. — Carcinoplax verdensis Rathbun, 1914, ♂ (15.7 × 21.4 mm) (ZRC 2019.0549), Philippines: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, posterior margin of epistome; E, left third maxilliped; F, dorsal view of carpus of right cheliped; G, thoracic sternum and pleon; H, outer view of chelae.

FIG. 15. — Carcinoplax verdensis Rathbun, 1914, ♀ (16.3 × 21.9 mm) (ZRC 2019.0546),Philippines: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, dorsal view of carpus of right cheliped; F, thoracic sternum and pleon; G, sternopleonal cavity and vulvae.

FIG. 13. — Carcinoplax verdensis Rathbun, 1914, holotype ovigerous ♀ (10.5 × 13.0 mm) (USNM 46167), Philippines: A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, posterior margin of epistome; E, left third maxilliped; F, dorsal view of carpus of right cheliped; G, thoracic sternum and pleon; H, sternopleonal cavity and vulvae; I, outer view of right chela; J, outer view of left chela.

FIG. 24. — Gonopods: A-D, Carcinoplax verdensis Rathbun, 1914, ♂ (14.9 × 20.2 mm) (ZRC 2019.0547), Philippines; E, F, C. verdensis, ♂ (18.0 × 24.4 mm) (MNHN-B10377), Philippines; G, H, C. verdensis, ♂ (13.0 × 18.0 mm) (MNHN-B10264), Philippines; I, J, C. polita Guinot, 1989, holotype ♂ (15.0 × 19.0 mm) (MNHN-B10141), Philippines; K, C. polita, ♂ (14.5 × 20.0 mm) (ZRC 2000.0173), Philippines; L-O, C. polita, ♂ (25.9 × 30.1 mm) (ZRC 2019.0545), Philippines. A, K, L, left G1 (ventral view); B, M, distal part of left G1 (ventral view); C, N, distal part of left G1 (dorsal view); E, G, I, right G1 (dorsal view); D, J, O, D, L, H, left G2; F, H, J, right G2. E-H, after Guinot (1989: figs 35A, B; 36A, B) (as C. aff. longipes); I, J, after Guinot (1989: fig. 37A, B). Scale bars: A, D, K, L, O, 1.0 mm; B, C, M, N, 0.5 mm; E, F, G, H, not to scale.