Chiromantes leptomerus, Davie, Peter J. F. & Ng, Peter K. L., 2013

Davie, Peter J. F. & Ng, Peter K. L., 2013, A review of Chiromantes obtusifrons (Dana, 1851) (Decapoda: Brachyura: Sesarmidae), with descriptions of four new sibling-species from Christmas Island (Indian Ocean), Guam and Taiwan, Zootaxa 3609 (1), pp. 1-25 : 19-21

Chiromantes leptomerus sp. nov.

( Figs 3 D–F, 4C, 5D, 6D, 7D, 8C, 9D, 13F–J)

Chiromantes obtusifrons —Lin et al. 2011: 45 (with colour photographs).

Material Examined. HOLOTYPE: NMNS-7028-001, male (16.8× 12.7 mm), Pingtung County, Hsiang Chiaowan, Taiwan, H.-C. Liu, 25.08.1999. PARATYPES: ZRC 2000.1860, 2 males (13.4× 10.3 mm, 16.4× 12.7 mm), west coast of Lanyu Island, Taiwan, calcareous rock terraces, spray zone, C.D. Schubart & H.-C. Liu, 20– 21.09.1999.—QM-W25699, male (16.2× 12.4 mm), female (18.1× 13.4 mm), data as for ZRC 2000.1860. NMMBA-3504a, 2 males (23.0× 18.3 mm, 16.7×13.0 mm), Hsiang-Chiau-Wan, Kenting, Pingtung County, Taiwan, C.C. Li, 23.08.2012.—ZRC 2012.0958, 2 females (21.0×15.7, 20.0× 14.9 mm), Siatanzai, Kenting, Pingtung County, Taiwan, 21°55’55.8”N 120°44’37.4”S, J.-H. Lee & W.-J. Wang, 6.08.2012.—NMNS, male (17.1×13.0 mm), female (20.5× 15.6 mm), Siatanzai, Kenting, Pingtung County, 21°55’36.6”N 120°44’21.8”S, Taiwan, J.-H. Lee & W.-J. Wang, 17.08.2012.—ZRC 2012.0959, male (18.1× 13.9 mm), Siatanzai, Kenting, Pingtung County, 21°55’36.6”N 120°44’21.8”S, Taiwan, J.-H. Lee & W.-J. Wang, 31.08.2012.—ZRC 2012.0960, male (17.8× 13.9 mm), ovigerous female (18.8× 14.2 mm), Siatanzai, Kenting, Pingtung County, 21°55’36.6”N 120°44’21.8”S, Taiwan, J.-H. Lee & W.-J. Wang, 31.08.2012.—ZRC 2012.0961, female (22.3× 16.6 mm), Hsiang- Chiau-Wan, Kenting, Pingtung County, Taiwan, P.K.L. Ng & C.-W. Lin, 1.10.2012.

NON-TYPE: RUMF-ZC-1351, male (16.1× 12.4 mm), Gazuda Beach, Hateruma I., Ryukyu Is., Japan, Y. Fujita, 2.05.2009.—RUMF-ZC-1386, 2 males (15.5×11.1, 13.2× 9.9 mm), beside Hateruma Port, Hateruma I., Ryukyu I., Japan, Y. Fujita, 19.04.2009.—RUMF-ZC-2075, male (16.9×13.0 mm), Dannu Beach, Yonagun Island, Ryukyu Islands, Japan, Y. Fujita, 15.11.2007.—RUMF-ZC-2076, male (19.7× 14.6 mm), Honba Coast, Minamidaito Island, Japan, Y. Fujita, 2.09.2008.—RUMF-ZC-2077, male (18.5× 13.9 mm), Honba Coast, Minamidaito Island, Japan, Y. Fujita, 2.09.2008.—RUMF-ZC-2078, male (10.9× 8.2 mm), Ubama Beach, Yonaguni Island, Ryukyu Islands, Japan, Y. Fujita, 16.11.2007.—RUMF-ZC-2079, male (17.2× 12.8 mm), Dannu Beach, Yonaguni Island, Ryukyu Islands, Japan, Y. Fujita, 15.11.2007.—RUMF-ZC-2080, male (12.5× 9.5 mm), Dannu Beach, Yonaguni Island, Ryukyu Islands, Japan, Y. Fujita, 15.11.2007.—RUMF-ZC-2082, female (16.9× 12.9 mm), Shimoji Island, Miyako Group, Ryukyu Islands, Japan, Y. Fujita, 23.09.2012.—RUMF-ZC-2083, female (15.6× 12.1 mm), Shimoji Island, Miyako Group, Ryukyu Islands, Japan, Y. Fujita, 23.09.2012.—RUMF-ZC-2089, female (18.0× 13.1 mm), Giza Banta, Okinawa Island, Ryukyu Islands, Japan, T. Maenosono, 2007.—RUMF-ZC-2090, 2 males (16.0×12.2, 14.1×11.0 mm), female (14.8× 11.6 mm), Kori Island, off Nakijin Village of Okinawa Island, Ryukyu Islands, Japan, T. Maenosono, 9.06.2010.—RUMF-ZC-2104, 2 males (17.5×13.7, 17.4× 12.9 mm), female (15.7× 12.1 mm), Muigah, Miyako Island, Ryukyu Islands, Japan, Y. Fujita, 4.05.2005.—ZRC, 6 males (largest 18.9× 14.5 mm, smallest 14.3× 10.8 mm), 5 females (largest 15.2× 11.3 mm, smallest 8.3× 7.1 mm), Muigah, Miyako Island, Ryukyu Islands, Japan, Y. Fujita, 4.07.2005.—RUMF-ZC-819, female (15.7×12.0 mm), Giza Banda, Yaese Town, Okinawa I., Ryukyu Is., Japan, T. Maenosono, 22.05.2007.

Diagnosis. Carapace transversely subovate, c. 1.3 times broader than long; dorsal carapace, lateral branchial regions markedly swollen; exorbital tooth moderately oblique, forming slight angle posteriorly marking widest point of carapace, most prominent in larger specimens; front c. 0.6 times carapace width, margin slightly to broadly concave in dorsal view, appears smooth but microscopically granular, with pair of prominent lateral swellings behind margin; supraorbital margin entire, semicircular; dorsal surface of cheliped carpus conspicuously granular; walking legs relatively short; P4 merus c. 2.3 times longer than wide; P5 merus similar, 2.2–2.3 times longer; propodus P4 propodus c. 2.8 times longer than wide; P5 propodus 2.4 times; male abdomen ( Fig. 13 F) moderately broad; somite 6 with divergent lateral margins, margins relatively evenly convex; somite 3 width 2.8 times basal width of telson; G1 ( Fig. 13 G–J) relatively slender, weakly tapering to broadly convex subdistal shoulder; distally slender, strongly bent to 45° angle; terminal process long, with dorsal margin concave, apex slightly flanged.

Description. Carapace transversely subovate, c. 1.3 times (range 1.26–1.35) broader than long; surface bare, lacking setal tufts; covered with fine, but distinct low granules becoming arranged into short striae posteriorly; mesogastric regions well defined; lateral carapace surface generally without obvious discrete oblique striae, except for strong, concave epibranchial sulcus beginning just behind exorbital tooth. Dorsal carapace, lateral branchial regions markedly swollen. Exorbital tooth triangular, pointed, outer margin long, moderately oblique, forming slight angle posteriorly marking widest point of carapace, most prominent in larger specimens; margin constricted behind, but no trace of second anterolateral tooth. Postfrontal lobes strongly demarcated, separated by broad grooves, median lobes similar in width to lateral lobes. Front c. 0.6 times carapace width (0.66 in holotype), markedly deflexed, margin slightly to broadly concave in dorsal view; laterally triangular, bluntly pointed; frontal margin emarginate, microscopically granular ( Fig. 8 C); surface somewhat concave behind but with pair of prominent lateral swellings behind frontal margin. Supraorbital margin entire, semicircular; secondary rim formed either side making a smooth, broadly triangular, deflexed central plate behind ocular peduncle. Eye not extending beyond exorbital tooth. Frontal plate protruding as a shelf; medial septum broad, largely covering anterior half of anterior half of epistome; antennae, antennules much reduced in size, lodged under overhanging front; basal antennular segment not much swollen; antennal, antennular basal segments adjacent, not separated by septum. Antennal flagellum very short, entering orbit.

Third maxillipeds with ischium, merus subequal in length; ischium with shallow longitudinal, curved, median sulcus. Inner margin of merus, ischium with long setae, proximal outer margin of ischium, base of exopod with dense setae; outer margin of merus with short scattered setae only. Exopod slender, hidden behind ishium, merus except near base, tip reaching half length of outer margin of merus, flagellum long, slender.

Chelipeds subequal, robust. Merus trihedral; posterior border broadly convex emarginate, minutely granular, without indication of subdistal spine or lobe; inner anterior border minutely granular, broadly triangular; outer surface broadly convex, with fine transverse striae but appearing almost smooth. Carpus subquadrilateral, inner angle moderately produced, apically granular; outer margin, dorsal surface conspicuously granular. Palm dorsal surface slightly striated along superior margin, with scattering of moderate sized granules, otherwise smooth, punctate. Palm outer surface broadly rounded, smooth; no indication of subventral longitudinal ridge. Palm inner face of males smooth except for curved projecting crest of large tubercles behind gape ( Fig. 6 D). Cutting margin of fixed finger with 3 or 4 blunt teeth, proximal 3 similar in size, distalmost larger, rounded, conical, placed medially; dactylus with 2 teeth proximally, distalmost large, third much smaller blunt tooth slightly distal of medial tooth of ventral finger. Dorsal surface of dactylus smooth. Fingers with chitinous tips; adult males with narrow but distinct gape when fingers closed.

Walking legs relatively short, broad, flattened; second, third pairs sub-equal, longer than other walking legs. Without setae except for scattering of short dark bristles on dactyli, ventral face of propodi. Dorsal margins of meri with blunt subdistal shoulder, but otherwise unarmed; outer surfaces of meri with minutely granular transverse striae. P4 merus c. 2.3 times longer than wide; P5 merus similar, 2.2–2.3 times longer. Carpi with 2 accessory carinae on outer surface but not strongly marked. P4 propodus c. 2.8 times longer than wide; P5 propodus 2.4 times longer than wide. Dactyli 0.8 times length of propodi, slightly recurved, terminating in acute chitinous tip.

Thoracic sternites ( Fig. 9 D) smooth, mostly bare of setae except for few scattered bristles; abdominal cavity reaching to thick transverse setal fringe at junction of sternites 3, 4. Male abdomen ( Fig. 13 F) moderately broad; telson broadly rounded apically, 1.1 times longer than wide, only slightly longer than somite 6; somite 6 c. 1.8 times wider than long, lateral margins divergent with margins relatively evenly convex; somites 3–5 trapezoidal, lateral margins of somites 4, 5 relatively straight, lateral margins of somite 3 convex; somite 3 width 2.8 times basal width of telson; somites 1, 2 transversely, longitudinally narrow.

G1 ( Fig. 13 G–J) relatively slender, almost straight, weakly tapering to broadly convex subdistal shoulder; distally slender, strongly bent to 45° angle; terminal process long, with dorsal margin concave, apex slightly flanged. G2 short, as for the genus.

Females. Chelipeds slightly smaller, less robust, lacking raised granular row on inner face of chela. Vulval morphology without clear species-specific characters.

Colour in life. ( Fig. 3 D–H). Carapace background colour of adult males varying from pale brown to a darker grey-green; females and smaller males mottled greyish white, sometimes yellowish. Upper surface of carapace and legs with some course blotches and streaks; a distinctive pattern of large dirty yellow to green blotches across anterior part of carapace. Chelae of adult males reddish-pink to purplish red overall, especially on dorsal surfaces and dactylus; smaller males and females with palm whitish to whitish-pink, dactylus always clearly tinged with red to pink in part or whole. Ocular peduncles similar to carapace; corneas light green to yellowish green.

Remarks. Easily separated from its sympatric Taiwanese congener, Chiromantes eurymerus , by its relatively narrower legs, but also by its more slender G1 with its markedly elongated tip, and other differences discussed further under that species account. The numerous features that distinguish this species from all other presently known species in this sibling complex are given in Table 1 .

Specimens from the Ryukyu Is. seem to show some minor variability in the proportions of the leg segments, with the meri of some individuals appearing a little broader than typical, and almost approaching the C. eurymerus condition. However, in all other characters, including the form of the thoracic sternum and G1, they appear to be typical C. leptomerus . Their live colours are also similar. Perhaps this could indicate some incipient population separation taking place between Taiwan and Japan, as has been observed for the mitten crab Eriocheir japonica (Varunidae) , with crabs from Okinawa proving to be genetically distinct from Taiwanese and Chinese populations (Xu et al. 2009). Twin species-pairs on either side of the deep-water strait between Taiwan and the Yaeyama Islands has now been observed for several crabs including Tmethypocoelis ceratophora and T. choreutes (Dotillidae) (Davie & Kosuge 1995), and Mictyris guinotae and M. brevidactylus (Mictyridae) (Davie et al. 2010). While we cannot discern any clear morphological grounds for separating the Japanese and Taiwanese populations of C. leptomerus for the moment, it will be interesting if future genetic studies may show some level of evolutionary divergence reflecting that observed for other populations and species between these two areas.

Etymology. Derived from the Greek leptos meaning “thin” and meros meaning “thigh”, and refers to the relatively more slender legs of this species compared to the other sympatric Taiwanese species, C. eurymerus sp. nov. It is used here as a noun in apposition.

Distribution. Only known from Taiwan and the Ryukyu Islands, southern Japan.

Ecology. Supratidal; calcareous rock terraces, spray zone. Found comingled with C. eurymerus sp. nov. in the same shore habitat; the nature and extent of niche separation has not been determined.

Figures

FIGURE 3. Colours in life. A – C, Chiromantes silus sp. nov., Guam; A, ZRC 2000.0573, female (15.2 × 11.2 mm); B, C, ZRC 2001.0742, male (15.7 × 11.7 mm). D – H, Chiromantes leptomerus sp. nov., D, RUMF-ZC- 2104, male (17.5 × 13.7 mm), Muigah, Miyako Island, Ryukyu Islands, Japan; E, RUMF-ZC- 2076, male (19.7 × 14.6 mm), Honba Coast, Minamidaito Island, Japan; F, male, southern Taiwan, specimen not kept; H, NMNS, male (17.1 × 13.0 mm), Siatanzai, Kenting, Pingtung County, Taiwan. I – J, Chiromantes eurymerus sp. nov., I, NMNS, male (17.5 × 13.4 mm); J, NMNS, male (16.7 × 12.3 mm), Siatanzai, Kenting, Taiwan. Photographs: B, C by H. - C. Liu; D – E by Y. Fujita; F – J by H. - T. Shih.

FIGURE 6. Inner views of chelae. A, Chiromantes obtusifrons (Dana, 1851), UFUF- 14837, male (17.7 × 13.2 mm), Hawaiian Is.; B, C. obtusifrons (Dana, 1851), ZRC 2002.0220, male (19.7 × 14.7 mm), Hawaiian Is.; C, C. silus sp. nov., ZRC 2012.0787, holotype male (16.3 × 12.8 mm), Guam; D, C. leptomerus sp. nov., NMNS 7028 - 001, holotype male (16.8 × 12.7 mm), Taiwan; E, C. eurymerus sp. nov., NMNS- 7028 - 002, holotype male (18.7 × 14.8 mm), Taiwan; F, C. garfunkel sp. nov., QM-W 29172, holotype male (17.0 × 13.0 mm), Christmas I.

FIGURE 8. Frontal margins (ventral views). A, Chiromantes obtusifrons (Dana, 1851), ZRC 2002.0220, male (19.7 × 14.7 mm), Hawaiian Is.; B, C. silus sp. nov., ZRC 2012.0787, holotype male (16.3 × 12.8 mm), Guam; C, C. leptomerus sp. nov., NMNS 7028 - 001, holotype male (16.8 × 12.7 mm), Taiwan; D, C. garfunkel sp. nov., QM-W 29172, holotype male (17.0 × 13.0 mm), Christmas I.

FIGURE 9. Ventral views of thoracic sternum and anterior parts of male abdomens. A, Chiromantes obtusifrons (Dana, 1851), UFUF- 14837, male (17.7 × 13.2 mm), Hawaiian Is.; B, C. obtusifrons (Dana, 1851), ZRC 2002.0220, male (19.7 × 14.7 mm), Hawaiian Is.; C, C. silus sp. nov., ZRC 2012.0787, holotype male (16.3 × 12.8 mm), Guam; D, C. leptomerus sp. nov., NMNS 7028 - 001, holotype male (16.8 × 12.7 mm), Taiwan; E, C. eurymerus sp. nov., NMNS- 7028 - 002, holotype male (18.7 × 14.8 mm), Taiwan; F, C. garfunkel sp. nov., QM-W 29172, holotype male (17.0 × 13.0 mm), Christmas I.

FIGURE 13. A – E, Chiromantes silus sp. nov., ZRC 2012.0787, holotype male (16.3 × 12.8 mm), Guam; F – J, C. leptomerus sp. nov., NMNS- 7028 - 001, holotype male (16.8 × 12.7 mm), Taiwan. A, F, male abdomen (somites 3 – 6, telson); B, G, ventral view of left G 1; C, H, dorsal view of left G 1; D, I, ventral view of distal part of left G 1; E, J, dorsal view of distal part of left G 1. All structures denuded. Scales: A – C, F – H, = 1.0 mm; D, E, I, J = 0.5 mm.