Chiromantes eurymerus, 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 : 21-24

Chiromantes eurymerus sp. nov.

( Figs 3 I, J, 4D, 5E, 6E, 7E, 9E, 14)

Material Examined. HOLOTYPE: NMNS-7028-002, male (18.7× 14.8 mm), west coast of Lanyu Island, Taiwan, calcareous rock terraces, spray zone, C.D. Schubart & H.-C. Liu, 20– 21.09.1999. PARATYPES: ZRC 2000.1823, Pingtung County, Hsiang Chiaowan, Taiwan, H.-C. Liu, 25.08.1999, male (18.2×14.0 mm), 2 females (17.0×13.2, 19.9×15.0 mm).—ZRC 2000.1822, male (13.3× 10.2 mm), Pingtung County, Hsiang Chiaowan, Taiwan, H.-C. Liu, 5.07.1999.—QM-W29171, male (20.0× 15.4 mm), west coast of Lanyu Island, Taiwan, calcareous rock terraces, spray zone, C.D. Schubart & H.-C. Liu, 20– 21.09.1999. NMMBA-3504b, male (19.3× 14.8 mm), female (22.6× 16.7 mm), Hsiang-Chiau-Wan, Kenting, Pingtung County, Taiwan, C.C. Li, 23.08.2012.—NMNS, 2 males (17.5×13.4, 16.7× 12.3 mm), Siatanzai, Kenting, Pingtung County, Taiwan, 21°55’36.6”N, 120°44’21.8”S, J.-H. Lee & W.-J. Wang, 17.08.2012.—ZRC 2012.0956, male (15.4× 12.3 mm), ovigerous female (18.0× 13.4 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.—NMNS, female (18.8× 13.6 mm), same data as ZRC 2012.0956.

NON-TYPE: ZRC 2012.0957, dried female exuvium (24.8× 18.7 mm), Dingtanzai, near nuclear power station, Kenting, Pingtung County, Taiwan, P.K.L. Ng, 4.10.2012.

Diagnosis. Carapace transversely subovate, c. 1.3 times broader than long; dorsal carapace, lateral branchial regions markedly swollen; exorbital tooth with outer margin broadly convex marking widest point of carapace; front c. 0.65–0.7 times carapace width, margin broadly convex in frontal view, but medial part relatively straight in dorsal view, appears smooth but microscopically granular, with pair of low lateral swellings behind margin; supraorbital margin entire, semicircular; dorsal surface of carpus of cheliped covered in small granules; walking legs relatively short; merus of P4 c. 2.0 times longer than wide; that of P5 similar at 2.0–2.1 times longer; propodus of P5 also 2.1–2.2 times; male abdomen ( Fig. 14 C) moderately broad; somite 6 with distolateral margins relatively straight, strongly divergent, margins convex overall; somite 3 width 3.1 times basal width of telson; G1 ( Fig. 14 E, G, H) markedly stout, with margins subparallel to obtusely angled subdistal shoulder; distally slender, strongly bent to 45° angle; terminal process short, not projecting past line of gonopod shaft, moderately tapering.

Description. Carapace transversely subovate, c. 1.3 times (range 1.29–1.32) 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 broadly convex marking widest point of carapace, margin not constricted behind (sometimes slightly flattened) such that entire lateral border appears convex, no trace of second anterolateral tooth. Postfrontal lobes well demarcated but relatively low, rounded, separated by broad grooves, median lobes similar in width to lateral lobes. Front c. 0.65–0.7 times carapace width (0.65 in holotype), markedly deflexed, margin broadly convex in frontal view, but medial part relatively straight in dorsal view; laterally triangular, bluntly pointed; frontal margin emarginate, microscopically granular but appearing relatively smooth; surface relatively flat behind, but with pair of low lateral swellings behind frontal margin. Supraorbital margin entire, semicircular but oblique medial section somewhat straight; 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 covered in small granules. Palm dorsal surface slightly striated along margin, with scattering of moderate sized granules, otherwise smooth, punctate. Palm outer surface broadly rounded, smooth; no indication of subventral longitudinal ridge. Inner face of palm of males smooth except for curved projecting crest of large tubercles behind gape ( Fig. 6 E). Cutting margin of fixed finger typically with 3 or 4 blunt teeth, proximal 3 similar in size, distal-most larger, rounded, conical, placed medially; dactylus with 2 teeth proximally, distal-most being large, third much smaller blunt tooth slightly distal of medial tooth of ventral finger. Dorsal surface of dactylus smooth. Fingers with tips chitinous; 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. Merus of P4 c. 2.0 times longer than wide; that of P5 similar at 2.0–2.1 times longer. Carpi with 2 accessory carinae on outer surface but not strongly marked. Propodus of P4 c. 2.1–2.2 times longer than wide; that of P5 also 2.1–2.2 times. Dactyli 0.8 times length of propodi, slightly recurved, terminating in acute chitinous tip.

Thoracic sternites ( Fig. 9 E) smooth, mostly bare of setae except for a few scattered bristles; abdominal cavity reaching to thick transverse setal fringe at the junction of sternites 3, 4. Male abdomen ( Fig. 14 C) moderately broad; telson broadly rounded apically, 1.2 times longer than wide, markedly longer than somite 6 (1.4–1.5 times); somite 6 c. 2.3 times wider than long, distolateral margins relatively straight, strongly divergent, margins convex overall; somites 3–5 trapezoid, lateral margins of somites 4, 5 relatively straight, lateral margins of somite 3 convex; somite 3 width 3.1 times basal width of telson; somites 1, 2 transversely, longitudinally narrow.

G1 ( Fig. 14 E, G, H) markedly stout, relatively straight, with margins subparallel to obtusely angled subdistal shoulder; distally slender, strongly bent to 45° angle; terminal process short, not projecting past line of gonopod shaft, moderately tapering. G2 short, as for the genus ( Fig. 14 F).

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. Carapaces of adult males and females are generally pale grey and white to yellowish-brown to yellowish-grey; with chelae of both sexes, notably dactylus, white, without obvious pink or red; eyes blue to bluish-green ( Fig. 3 I, J).

Remarks. Chiromantes eurymerus sp. nov. is separated from its sympatric Taiwanese congener, C. leptomerus sp. nov., by its obviously broader legs, and by its stouter G1 with its much shortened tip, a unique character within the species-group, and which easily separates it from all other species described here. Numerous other features that distinguish C. eurymerus from other related species are given in Table 1 . Chiromantes leptomerus sp. nov. is similar to C. obtusifrons sp. nov. in having the outer margin of the exorbital tooth broadly convex, and in not having the carapace laterally constricted behind the exorbital tooth. It differs from that species by having a less conspicuously granular carapace and claws, and by the stouter G1 already mentioned.

Both species also appear to be distinctively coloured. In C. leptomerus , corneas are typically light green to yellowish green ( Fig. 3 G, H), whereas in C. eurymerus , the eyes are blue to bluish-green ( Fig. 3 J). The colours of the carapace and chelae also appear different, although the reliability of these characters will need to be tested with more specimens. The carapace background colour of adult males of C. leptomerus varies from pale brown to a darker grey-green ( Fig. 3 D–H); whereas in C. eurymerus adult males (and females) are generally pale grey and white to yellowish-brown to yellowish-grey ( Fig. 3 I, J). Finally, in C. leptomerus the chelae of adult males are often reddish-pink to purplish red overall, especially on the dorsal surfaces and dactyli ( Fig. 3 H); whereas in C. eurymerus the chelae of both sexes, and notably the dactyli are yellowish to off-white, without any obvious pink or red tinging ( Fig. 3 J).

Etymology. Derived from the Greek eury meaning “broad”, and meros meaning “thigh”, and refers to the relatively shorter and stouter legs of this species compared to the other sympatric Taiwanese species, C. leptomerus sp. nov. It is used here as a noun in apposition.

Distribution. So far only known from Taiwan. We are pleased to thank Peter Castro for his careful and constructive criticism of the manuscript.

Ecology. Supratidal; calcareous rock terraces, spray zone. Found comingled with C. leptomerus 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 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 14. Chiromantes eurymerus sp. nov., NMNS- 7028 - 002, holotype male (18.7 × 14.8 mm), Taiwan. A, left third maxilliped; B, left side of anterior thoracic sternum; C, male abdomen (somites 3 – 6, telson); D, ventral view of left G 1; E, dorsal view of left G 1; F, left G 2; G, ventral view of distal part of left G 1; H, dorsal view of distal part of left G 1. All structures denuded. Scales: A – F = 1.0 mm; G, H = 0.5 mm.