Tiwaripotamon hamyen, Do & Nguyen & Dang, 2017

Do, Van Tu, Nguyen, Tong Cuong & Dang, Van Dong, 2017, Two new species of freshwater crabs of the genus Tiwaripotamon Bott, 1970 (Crustacea, Decapoda, Brachyura, Potamidae) from northern Vietnam, Raffles Bulletin of Zoology 65, pp. 455-465 : 461-464

Tiwaripotamon hamyen , new species

( Figs. 6–8 )

Material examined. Holotype: male (41.7 × 32.3) (IEBR- FC THx01), 22°03.341′N 105°09.638′E, Binh Xa commune, Ham Yen district, Tuyen Quang province, Vietnam, 232 m, coll. Chu H. Q., 27 August 2015.

Paratypes. 5 males (37.2 × 28.4, 36.4 × 28.3, 35.7 × 27.8, 35.0 × 27.3, 29.4 × 23.2) ( IEBR-FC THx02–06), 3 females (43.8 × 33.0, 40.6 × 29.8, 40.0 × 30.8) ( IEBR-FC THx07–09), same data as holotype.

Comparative material. Tiwaripotamon edostilus Ng & Yeo, 2001: 1 male (26.1 × 21.4), ( IEBR-FC TE01 ), Cat Ba island , Hai Phong city, Vietnam, 15–170 m, coll. V. T. Do, 18–19 March 2013. Tiwaripotamon vietnamicum ( Dang & Ho, 2002) : 2 males (44.5 × 32.8, 41.3 × 31.2), ( IEBR-FC TVn01, NCHUZOOL 13612), Cuc Phuong National Park , Ninh Binh province, Vietnam, 500 m, coll. V. T. Do, 14 May 2013 . Tiwaripotamon vixuyenense Shih & Do, 2014: 1 male (26.4 × 20.5) ( IEBR-FC TVx01), Tung Ba commune, Vi Xuyen district, Ha Giang province, Vietnam, 758 m, coll. N.L. Doan & X.N. Nguyen, 2 July 2013 . Tiwaripotamon pluviosum : 1 male (32.2 × 23.2) ( IEBR-FC TPx01), 22°43′466″N 106°39′051″E, Coong village , Duc Quang commune, Ha Lang district, Cao Bang province, Vietnam, 572 m, coll. T.C. Pham, 7 June 2014 .

Diagnosis. Medium-sized (CW: 28–44 mm). Carapace about 1.3 times broader than long, transverse, low; dorsal surface flat, glabrous; regions poorly defined, cervical groves indiscernible, H-shaped depression very shallow. Anterolateral margins of carapace very weakly serrated (in males) and nearly smooth (in females); postorbital cristae indistinct, smooth, not obviously confluent with epibranchial tooth. Epibranchial tooth very small, low, not prominent. Posterior margin of epistome with low median blunt tooth. Exopod of third maxilliped with very short flagellum, about 0.1 times width of merus. Ambulatory legs long and slender; 4 th pair with length of merus about 4.1 times width. G1 terminal segment curved outwards, hook-shaped, without dorsal flap in posterior part. Telson triangular with lateral margins gently convex.

Description. Carapace transverse, low, about 1.3 time broader than long (n=9); dorsal surface flat, glabrous; regions poorly defined, cervical grooves indiscernible, H-shaped depression very shallow, indiscernible ( Fig. 5A ). Epigastric cristae very low, weak and smooth, separated by very short, shallow groove that opens up into inverted V-shape posteriorly, no groove between epigastric cristae and postorbital cristae; postorbital cristae weakens, indistinct, smooth, not obviously confluent with epibranchial tooth; regions behind epigastric and postorbital cristae smooth ( Fig. 5A ). Frontal margin slightly emarginate medially; frontal region turned downwards, smooth; supra- and infraorbital margins cristate, supraorbital margin sinuous, infraorbital margin almost straight; orbital region smooth, relatively narrow; subhepatic and subbranchial regions smooth ( Figs. 5A , 6B ). External orbital angle triangular, outer margin convex, weakly cristate to smooth; epibranchial tooth very small and low, separated from external orbital angle by narrow and shallow triangular cleft; anterolateral margin slightly convex, very weakly serrated (in males) and nearly smooth (in females); posterolateral margin entire, almost straight, not strongly convergent posteriorly; branchial and metabranchial regions smooth ( Figs. 5A , 6B ). Epistome anterior margin with median triangle; posterior margin with low median blunt tooth, slightly crenulated laterally, with outer part deeply concave ( Fig. 5B ).

Ischium of third maxilliped subrectangular, about 1.4 times longer than broad, with shallow longitudinal median sulcus; merus squarish, longer than half (0.6 times) of ischium length; exopod relatively short, equal or slightly exceeding upper edge of ischium, with very short flagellum, about 0.1 times width of merus (n=9) ( Fig. 5C ).

Chelipeds ( Fig. 5D ) subequal; outer surface smooth to slightly rugose, subequal in length to palm, tips overlapping. Right chelipeds with length of palm+pollex about 3.1 times palm height, carpus with smooth outer surface, with strong, obliquely directed, subdistal spine on inner margin; merus with serrated edges, without subterminal spine.

Ambulatory legs ( Fig. 5A ) glabrous, long and slender; second leg with dactylus about 8.4 times longer than proximal width, propodus about 4.7 times longer than broad and equal or slightly longer than dactylus, carpus about 0.6 times length of dactylus, merus about 1.4 times longer than dactylus (n=9); fourth leg with dactylus about 8.3 times longer than proximal width, propodus slightly longer than dactylus, carpus about 0.7 times length of dactylus (n=8), merus without serrated upper margins, about 4.1 times longer than proximal width (n=8) and about 1.4 times longer than dactylus (n=8).

Suture between anterior thoracic sternites 2 and 3 complete, distinct, slightly convex in the middle; groove between sternites 3 and 4 complete, distinct ( Fig. 7A ). Male abdominal cavity reaching imaginary line joining posterior points of cheliped bases (below the suture between thoracic sternites 3 and 4) ( Fig. 7B ).

Male abdomen broadly triangular; telson triangular, broader than long (about 1.4 times), lateral margins gently convex, tip rounded, subequal in length to sixth segment; segment 6 with proximal width about 2.2 times length, lateral margins almost straight; lateral margins of segments 4 to 5 straight; lateral margins of segment 3 gently convex ( Fig. 6A ).

Gl gently sinuous, reaching just to over half of the fourth sternum; terminal segment slender, about 0.4 times length of subterminal segment, about 2.9 times longer than proximal width, without dorsal flap, curved outwards, hook-shaped, opening on tip visible from dorsal and ventral views, distal part of groove for G2 visible on ventral side, tip truncated; subterminal segment relatively slender, sinuous, without neck-like distal part ( Figs. 6B , 7 A–D). G2 shorter than G1 (0.9 times length of G1) with distal segment about 0.3 times length of basal segment ( Fig. 7E, F ). Female gonopore in thoracic sternite 6, round, without operculum, opened posterio-mesially ( Fig. 6C ).

Etymology. The new species is named after the type locality, Ham Yen. The name is used as a noun in apposition.

Live colouration. Carapace and chela milky to light gray, ambulatory legs vary from milky to light gray or purple mixed light orange ( Fig. 8 A–D).

Ecological notes. This species inhabits limestone mountains. Our observation of this species and other Tiwaripotamon species from Vietnam confirm that they have terrestrial habits. They were often found far from water sources like streams and ponds. We observed a female T. edostilus carrying juveniles walking on the forest floor not close to any water body. It means these juveniles did not develop in streams or ponds.

Remarks. Tiwaripotamon hamyen is easily separated from all other Tiwaripotamon species by: (1) median tooth of epistome posterior margin is low and blunt (vs. median tooth of epistome posterior margin is triangular); (2) ambulatory legs are relatively less longer and slender compared to the congeners (the merus of 4 th pair leg of this species is about 4.1 longer than broad compared to 4.3 for T. pingguoense , 4.5 for T. annamense (see Do et al., 2016), 4.8 for T. pluviosum , 5.1 times for T. vietnamicum , 5.3 times for T. xiurenense (unpublished data), 5.6 times for large T. edostilus specimens, and 6.5 for T. vixuyenense ( Shih & Do, 2014) ; (3) G1 terminal segment is curved outwards, hook shape (vs. curved upwards, not hook shape) ( Dai & Naiyanetr, 1994: Figs. 1–2 ; Ng & Yeo, 2001: Figs. 1–5 ; Shih & Do, 2014: Figs: 2–7; Dang & Ho, 2012: Fig. 78; Do et al., 2016: Figs: 1–5).

Figures

Fig. 6. Tiwaripotamon hamyen, new species, holotype, male (CW 41.7 mm), IEBR-FC THx01. A, ventral view; B, sternoabdominal cavity showing G1s and G2s; C, female gonopore (CW 43.8 mm), IEBR-FC THx07.

Fig. 7. Tiwaripotamon hamyen, new species, holotype, male (CW 41.7 mm), IEBR-FC THx01. A–F, right G1: A, ventral view; B, ventral view of terminal segment; C, dorsal view; D, dorsal view of terminal segment; E, right G2; F, right G2 of terminal segment.

Fig. 8. A–D, Tiwaripotamon hamyen, new species, with differences living colour in carapace and ambulatory legs.

Fig. 5. Tiwaripotamon hamyen, new species, holotype, male (CW 41.7 mm), IEBR-FC THx01. A, carapace, dorsal view; B, frontal view; C, left third maxilliped; D, chela outer view.

Fig. 1. Collection sites of Tiwaripotamon xuanson, new species and T. hamyen, new species.

Fig. 2. Tiwaripotamon xuanson, new species, holotype, male (CW 33.1 mm), IEBR-FC TXx01. A, carapace, dorsal view; B, frontal view; C, left third maxilliped; D, chela outer view.

Fig. 3. Tiwaripotamon xuanson, new species, holotype, male (CW 33.1 mm), IEBR-FC TXx01. A, ventral view; B, sternoabdominal cavity showing G1s and G2s; C, female gonopore (CW 32.6 mm), IEBR-FC TXx06; D, A habitat in Ten mountain, Xuan Son National Park, Thanh Son District, Phu Tho Province, Vietnam.

Fig. 4. Tiwaripotamon xuanson, new species, holotype, male (CW 33.1 mm), IEBR-FC TXx01. A–F, right G1: A, ventral view; B, ventral view of terminal segment; C, dorsal view; D, dorsal view of terminal segment; E, right G2; F, right G2 of terminal segment.