Heterochelamon tessellatum, Naruse, Tohru, Zhu, Chunchao & Zhou, Xianmin, 2013

Naruse, Tohru, Zhu, Chunchao & Zhou, Xianmin, 2013, Two new species of freshwater crabs of the genus Heterochelamon Türkay & Dai, 1997 (Crustacea: Decapoda: Brachyura: Potamidae) from Guangxi Zhuang Autonomous Region, southern China, Zootaxa 3647 (4), pp. 567-576 : 568-573

Heterochelamon tessellatum n. sp.

( Figs. 1–3 )

Material examined. Holotype: NCU MCP 2012.0003, male, 29.4 × 35.6 mm, Ting xian creek, Dong Men Zhuang, Shuangluo Village, Sanli Town, Sanli Town, Shanglin County, Guangxi Zhuang Autonomous Region, 23°33ʹ44ʺN 108°35ʹ46ʺE, 105 m asl, coll. Lijun Shi, 14 Aug. 2006.

Paratypes: 1 male, NCU MCP 2012.0004, 22.6 × 27.5, 1 male, NCU MCP 2012.0005, 24.5 × 29.6 mm, 1 male, RUMF-ZC-2317, 24.2 × 29.2 mm, 1 male, NCHUZOOL 13571, 27.0 × 32.3 mm, 1 female, NCHUZOOL 13572, 24.4 × 28.7 mm, same data as holotype.

Description. Carapace ( Fig. 1 a) broader than long, widest across anterior third of carapace, CW 1.18–1.21 times (mean = 1.20, n = 6) CL; dorsal surface glabrous, longitudinally convex, transversely. Epigastric cristae low, oblique, postorbital cristae absent, H-shaped gastric groove shallow. Front directed antero-ventrally, anterior margin weakly bilobed. Supra-, infraorbital margins ( Fig. 1 a, b) cristate, granular, crista lower at lateral end of infraorbital margin, suborbital region smooth, pterygostomial regions slightly rugose. External orbital angle sharp, long, anterolateral margin convex laterally, cristate, lined with relatively sharp teeth.

Epistome ( Fig. 1 b) with cristate posterior margin, medial lobe projected.

Antennular fossa narrow, oblong.

Thoracic sternite 2 slightly lower than sternite 3; sternites 3, 4 demarcated by shallow, oblique depressions. Abdominal cavity reaching imaginary line joining posterior third of cheliped coxae ( Fig. 2 a), cavity relatively narrow, distance between inner ends of sutures of thoracic sternites 4/5 about half distance between sternal condyles; sternal condyle placed middle of thoracic sternite 5.

Third maxilliped rectangular, mid-length of ischium more than 2 times that of merus, exopod reaching proximal third of outer margin of merus, flagellum long, exceeding mesial end of merus.

Chelipeds strongly unequal in male ( Figs. 1 a, 2b), major chela with strongly curved fingers. Merus of major cheliped rather smooth, with small subdistal denticle on ventromesial margin. Carpus with strong inner angle, with proximoventral small granule. Palm ( Fig. 2 b) moderately convex, high, fingers strongly curved, forming oblong gape, cutting edge lined regularly with small teeth.

Ambulatory legs ( Figs. 1 a) moderately long, second, third legs longest when stretched laterally; meri with small subdistal angle on anterior margin; dactyli as long as respective propodi, subdistal spine of outer dorsal margin of fourth leg as long as distal spine, placed slightly inner with respect to outer dorsal margin.

Male first abdominal segment with transverse ridge; third segment widest; telson triangular, width 1.27 times (n = 1) length, 1.27 times (n = 1) longer than sixth segment, sixth segment width 2.03–2.07 times (mean 2.05, n = 2) length.

G1 ( Figs. 3 a, b) with slightly sinuous subdistal segment, knuckle-shaped distal segment; distal segment gently bent inwards, length about three-fifths of subdistal segment. G2 ( Fig. 3 c) about same length of G1, strongly curved medially; distal flagellum about half of subdistal segment.

Vulva oblong, large.

Colouration. Only preserved material was examined; no fresh colour was recorded. After a two-year preservation in 75% ethanol, however, olive background colour were still recognizable, together with a reddish mosaic patterns on the dorsal surface and suborbital and subhepatic regions of the carapace ( Fig. 1 ). The mosaic patters are also seen mainly on the upper surfaces of chelipeds and the ambulatory legs.

Etymology. The specific epithet ‘ tessellatum ’ is Latin for ‘mosaic’, referring to its mosaic-like colour pattern of the carapace and appendages.

Ecological note. According to the collector of H. tessellatum , the site was a relatively small and unnamed branch of a stream from a river near northeast of the village with karst terrain. The creek is about 1 m wide and 0.5 m deep, with sandy bed and aquatic vegetation.

Remarks. Heterochelamon tessellatum is morphologically most similar to H. yangshuoense Türkay & Dai, 1997 , in its strongly gaping fingers of the male major chela and fist-shaped distal end of the G1 (Türkay & Dai, 1997: fig. 6–2, 6–5, 6–6). The G1 of the holotype of H. yangshuoense , however, was drawn as both subterminal and terminal segments are straight, including a median groove for the G2 on the ventral surface (Türkay & Dai 1997, fig. 6–5), while that of H. tessellatum has slightly sinuous subterminal segment and strongly bent terminal segment ( Fig. 3 c, d). The holotype of H. tessellatum (CW 35.6 mm) is larger than the holotype of H. yangshuoense (CW 29.4 mm). Small males of H. tessellatum tend to have stronger bent at the distal segment of the G1, which indicates that the differences of the bent observed in H. tessellatum and H. yangshuoense appears to be not a sizerelated. Furthermore, the supraorbital margin of H. tessellatum shows shallower concavity in dorsal view ( Fig. 1 a), while that of H. yangshuoense is much deeper (Türkay & Dai, 1997: pl. 1–7).

Heterochelamon castanea n. sp. ( Figs. 4–6 )

Material examined. Holotype: male, 21.8 × 26.7 mm, NCU MCP 2012.0001, Lituan Village, Baiming Town, Liujiang County, Liujiang City, Guangxi Zhuang Autonomous Region, 24°08ʹ33ʺ N 109°16ʹ16ʺ E, 122 m asl, coll. Xiaojia WeiAug. 2006.

Paratypes: 1 male, 21.6 × 26.2 mm, 1 female, 18.4 × 22.8 mm, RUMF-ZC-1971, 1 female 20.1 × 24.1 mm, NCU MCP 2012. 0 0 0 2, same data as holotype.

Description. Carapace ( Fig. 4 a) broader than long, CW 1.20–1. 24 times (mean 1.22, n = 4) CL; dorsal surface convex longitudinally, transversely, smooth, sparsely punctate; epigastric region slightly raised, postorbital region barely raised, cervical groove indiscernible, H-shaped gastric groove shallow but distinct. Front directed anteriorly, concave medially. Front, supra-, infraorbital margins ( Fig. 4 b) cristate, granulated, crista lower at lateral end of infraorbital margin; suborbital, pterygostomial regions rough, sparsely granulated. External orbital angle low, strong, almost right angle, directed anterior-inward, outer margin about 2 times longer than inner margin; epibranchial tooth distinct, sharp, anterolateral margin cristate, distinctly granulated, shorter than posterolateral margin, margin slightly turning upwards. Antennular fossa oblong, inferior margin convex sublaterally; epistome granulated, with posterior margin cristate, granulated, with 3 lobes, median longest, triangular.

Mandible palp three-segmented, with terminal segment simple. Third maxilliped rectangular, midlength of ischium about 2 times that of merus, exopod reaching slightly shorter than half length of merus, flagellum long.

Thoracic sternites 2, 3 ( Fig. 5 a) demarcated by distinct suture, sternites 3, 4 discernible by shallow but clear groove. Abdominal cavity reaching imaginary line joining posterior third of cheliped coxae, cavity relatively narrow, distance between inner ends of sutures of thoracic sternites 4/5 wider than third length of distance between sternal condyles; sternal condyle positioned slightly proximal to middle of thoracic sternite 5; thoracic sternite 8 demarcated medially by uninterrupted longitudinal median line, without transverse ridge at inner ends of sutures between thoracic sternites 7, 8.

Chelipeds subequal in males ( Fig. 4 a), major cheliped stouter than minor; merus granular on dorsal, ventral margins, granules larger on dorsal margin, subdistal tooth on ventral surface small; carpus with long, sharp inner angle, small protuberance below base of inner angle; palm with moderately convex outer surface, smooth, height slightly shorter than palm length; fingers shorter than palm, narrow gape when chela closed, cutting edge lined with low teeth ( Fig. 5 b).

Ambulatory legs ( Fig. 4 a) moderately long, almost glabrous, second, third legs longest when stretched laterally, surfaces rough, merus with low subdistal angle on anterior margin; dactyli longer than respective propodi. Subdistal tooth on upper-outer raw of teeth of P5 larger than other teeth, slightly positioned inward.

Male first abdominal segment with transverse ridge; third segment widest, lateral margins of third to six segments almost straight, convergent distally; telson triangular, lateral margin slightly concave, width 1.29–1.31 times length (mean 1.22, n = 2), 1.35–1.42 times (mean 1.38, n = 2) longer than sixth segment, sixth segment width 2.23–2.28 times length (mean 2.26, n = 2). G1 ( Figs. 6 a, b) slender, straight. Distal segment slightly shorter than third of G1, distally bulging. Groove for G2 running mid-line of ventral surface, weakly curving laterally at proximal part of bulge, turning mesially to subdistal opening. Dorsal side with narrow synovial membrane between distal, subdistal segment. G2 ( Fig. 6 c) longer than G1, flagellum about third length of G2.

Vulva oblong, large.

Etymology. The specific epithet castanea is Latin for “chestnut” and refers to its maroon body colour. The name is used as a noun in apposition.

Ecological note. According to the collector of H. castanea n. sp., the collection site was a small ditch about 1 km from Lituan Village. There were many planted rice and lotus roots on both sides of the ditch. The ditch was about 1 m wide, about 0.3 m deep, with a muddy bed. The crabs seem to be more common among aquatic grasses than from holes on muddy sediments.

Remarks. The G1 of Heterochelamon castanea n. sp. is morphologically close to that of H. guangxiense Türkay & Dai, 1997 , in its slender shape and slightly bulged distal end ( Fig 6 a, b; Türkay & Dai, 1997: fig. 5–4, 5– 5). The new species can be, however, distinguished from H. guangxiense by an acute and triangular external orbital tooth ( Fig. 4 a) (tooth blunt and semicircular lobe-like in H. guangxiense, Türkay & Dai 1997 : pl. 1–6), epibranchial tooth distinct but not separated from external orbital tooth by wide gape ( Fig. 4 a) (epibranchial tooth separated by distinct V- to U-shaped gape in H. guangxiense, Türkay & Dai 1997 : pl. 1–6), and distal segment of G1 straight ( Fig. 6 a, b) (slightly directed mesially in H. guangxiense, Türkay & Dai 1997 : fig. 5–4, 5–5).

Figures

FIGURE 1. Holotype of Heterochelamon tessellatum n. sp.: a, dorsal view; b, frontal view. Photographs were taken in Dec. 2008 after more than a two-year preservation in 75 % ethanol.

FIGURE 2. Holotype of Heterochelamon tessellatum n. sp.: a, thorax, thoracic cavity, and gonopods; b, major chela.

FIGURE 3. Holotype of Heterochelamon tessellatum n. sp.: a, left G 1, ventral view; b, left G 1, dorsal view; c, left G 2, ventral view. Scales = 1.0 mm.

FIGURE 4. Holotype of Heterochelamon castanea n. sp.: a, dorsal view; b, frontal view. Photographs were taken in Jun. 2012 after more than a six-year of preservation in 75 % ethanol.

FIGURE 5. Holotype of Heterochelamon castanea n. sp.: a, thorax and abdomen; b, major chela.

FIGURE 6. Holotype of Heterochelamon castanea n. sp.: a, left G 1, ventral view; b, left G 1, dorsal view; c, left G 2, ventral view. Scales = 1.0 mm.