Tiwaripotamon xuanson, 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 : 455-461

publication ID	https://doi.org/ 10.5281/zenodo.4504476
publication LSID	lsid:zoobank.org:pub:2CB78941-EAAD-461E-BFFC-D4262A16AE3A
persistent identifier	https://treatment.plazi.org/id/7547FEA9-A65A-4327-9433-5A3EDE1065C7
taxon LSID	lsid:zoobank.org:act:7547FEA9-A65A-4327-9433-5A3EDE1065C7
treatment provided by	Carolina
scientific name	Tiwaripotamon xuanson
status	sp. nov.

Treatment

Tiwaripotamon xuanson View in CoL , new species

( Figs. 2–4 View Fig View Fig View Fig )

Material examined. Holotype: male (33.1 × 25.6) (IEBR- FC TXx01), 21°7′7.4″N 104°57′7.6″E, Ten Mountain , Xuan Son National Park , Thanh Son district, Phu Tho province, Vietnam, 469 m, coll. V. T. Do, 19 September 2014. GoogleMaps

Paratypes: 2 males (31.6 × 23.7, 32.9 × 25.3), 3 females (30.2 × 23.2, 29.1 × 22.4, 32.6 × 24.5) ( IEBR-FC TXx02- 06), same data as holotype GoogleMaps .

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 Do et al, 2016: 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. Small-sized (CW: 29–33 mm). Carapace about 1.3 times broader than long, transverse, low, dorsal surface relatively flat, glabrous; regions not well-defined, cervical groves indiscernible; postorbital cristae indistinct, rounded, smooth, not obviously confluent with epibranchial tooth; external orbital angle triangular, with acute tip; epibranchial tooth very small, low; anterolateral margins of carapace very weakly serrate on anterior part. Ambulatory legs long and slender; 4 th pair with length of merus about 5.6 times width. Suture between sternites 3 and 4 distinct, demarcated as a deep groove in the middle. Telson broadly triangular with lateral margins gently convex. G1 terminal segment upcurved, subconical, without dorsal flap in posterior part.

Description. Carapace transverse, low, about 1.3 time broader than long (n=6); dorsal surface relatively flat; glabrous; regions not well-defined, cervical grooves undiscernible, H-shaped depression shallow but distinct ( Fig. 2A View Fig ). Epigastric cristae very weak, indistinct, not sharp, smooth to very weakly rugose, separated by short, shallow groove that opens up into inverted V-shape posteriorly, no groove between epigastric cristae and postorbital cristae; postorbital cristae indistinct, rounded, smooth, not obviously confluent with epibranchial tooth, weakens without breaking up into granules and rugae just before epibranchial tooth; regions behind epigastric and postorbital cristae smooth ( Fig. 2A, B View Fig ). Frontal margin broadly emarginate medially; frontal region turned downwards, appearing relatively narrow from dorsal view, smooth; supra- and infraorbital margins distinctly cristate, supraorbital margin sinuous, infraorbital margin almost straight; orbital region smooth, relatively narrow; eyes normal; subhepatic and subbranchial regions smooth ( Fig. 2B View Fig ). External orbital angle triangular, with acute tip, outer margin convex, weakly cristate to smooth; epibranchial tooth very small and low but distinct, separated from external orbital angle by a narrow and shallow triangular cleft; anterolateral margin slightly convex, very weakly serrate on anterior part; posterolateral margin entire, almost straight, not strongly convergent posteriorly; branchial and metabranchial regions smooth ( Fig. 2A View Fig ). Epistome anterior margin with median triangle; posterior margin with low median triangular tooth, slightly crenulated laterally, with outer part deeply concave ( Fig. 2B View Fig ).

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, with concave outer surface; palp normal; exopod relatively short, slightly exceeding upper edge of ischium, blunt tooth on distal part of inner margin weakly developed, with short but distinct flagellum, shorter than half width (0.4) of merus ( Fig. 2B, C View Fig ).

Chelipeds subequal, with outer surface smooth, subequal in length to palm, tips overlapping. Right chelipeds with length of palm+pollex about 3.0 times palm height, carpus with smooth outer surface, with strong, obliquely directed, subdistal spine on inner margin; merus with serrated edges, without subterminal spine ( Fig. 2D View Fig ).

Ambulatory legs ( Fig. 2A View Fig ) glabrous, conspicuously long and slender; all dactyli and propodi with obvious spines in both upper and bottom margins; second leg with dactylus about 10.1 times longer than proximal width, propodus about 6.2 times longer than broad and about 1.1 times longer than dactylus, carpus about 0.6 times length of dactylus, merus about 1.4 times longer than dactylus (n=6); fourth leg with dactylus about 9.5 times longer than proximal width, propodus about 0.9 times length of dactylus, carpus about 0.6 times length of dactylus (n=6), merus without serrated upper margins, about 5.6 times longer than proximal width (n=6) and about 1.3 times longer than dactylus (n=6).

Suture between anterior thoracic sternites 2 and 3 complete, distinct, convex in the middle; groove between sternites 3 and 4 distinct, demarcated as a deep groove ( Fig. 3A View Fig ); thoracic sternites 5 and 6 medially interrupted; sternites 7 and 8 medially separated by distinct longitudinal median suture. Male abdominal cavity reaching imaginary line joining posterior points of cheliped bases (below the suture between thoracic sternites 3 and 4) ( Fig. 3B View Fig ). Tubercles of male abdominal-locking mechanism positioned in thoracic sternite 5 ( Fig. 3B View Fig ).

Male abdomen broadly triangular; telson broadly triangular, broader than long (about 1.6 times), lateral margins gently convex, tip rounded, subequal in length to sixth segment; segment 6 with proximal width about 2.5 times length, lateral margins almost straight; lateral margins of segments 4 to 5 straight; lateral margins of segment 3 gently convex ( Fig. 3A View Fig ).

Gl sinuous, reaching to the tubercle of the fifth sternum; terminal segment upcurved, about 0.3 times length of subterminal segment, about 2.6 times longer than proximal width, without dorsal flap, subconical; subterminal segment relatively slender, sinuous, without neck-like distal part and subdistal cleft or shelf on outer margin ( Figs. 3B View Fig , 4 View Fig A–D). G2 slightly shorter or equal with G1, with distal segment about 0.4 times length of basal segment ( Fig. 4E, F View Fig ). Female gonopore in thoracic sternite 6, subovate, without operculum, opened posterio-mesially; anterio-external margin partially covered by raised rim; posterio-mesial margin surrounded by a low raised rim ( Fig. 3C View Fig ).

Etymology. The new species is named after the type locality, Xuan Son National Park. The name is used as a noun in apposition.

Live colouration. Carapace reddish, chela and ambulatory legs red.

Ecological notes. This species inhabits limestone mountains far from water bodies, on the forest floor. One specimen was found in a fallen dead tree ( Fig. 5 View Fig ). The other specimens were found in rock cavities and under leaf litter.

Remarks. The carapace shape of the new species is relatively similar with T. pluviosum . However, the G1 of these two species obviously different (G1 terminal segment is upcurved or upturned, about 0.30 times length of subterminal segment and 2.6 times longer than proximal width vs. strongly upcurved, about 0.34 times length of subterminal segment and 3.0 times longer than proximal width in T. pluviosum ) ( Fig. 4 View Fig A–D; cf. Do et al., 2016: Figs. 2–3 View Fig View Fig ).

Compared to T. araneum , this new species can be distinguished by a suite of characteristics: carapace more transverse, about 1.4 times broader than long; anterolateral margins of carapace very weakly serrate; branchial and metabranchial regions smooth; epistome posterior margin outer part deeply concave; ischium of third maxilliped subrectangular, about 1.4 times longer than broad (vs. carapace slightly transverse, about 1.24 times broader than long; anterolateral margins of carapace distinctly serrated in upper part; branchial and metabranchial regions weakly rugose; epistome posterior margin outer part gently concave; ischium of third maxilliped squarish, about 1.2 times longer than broad) ( Fig. 2 View Fig A–C; cf. Ng & Yeo, 2001: Figs. 2C View Fig , 3 View Fig ). Compared to T. annamense , the new species showed differences in the following characteristics: anterolateral margins of carapace very weakly serrate; ischium of third maxilliped subrectangular, about 1.4 times longer than broad; suture between sternites 3 and 4 distinct, demarcated as a deep groove; lateral margins of telson gently convex; terminal segment upcurved, stouter, about 0.3 times length of subterminal segment, about 2 times longer than proximal width (vs. anterolateral margins of carapace distinctly serrated; ischium of third maxilliped squarish, about 1.2 times longer than broad; suture between sternites 3 and 4 absent; lateral margins of telson are gently concave; terminal segment more upcurved, more slender, about 0.4 times length of subterminal segment, about 2.3 times longer than proximal width) ( Figs. 2 View Fig A–C; 4A–D; cf. Ng & Yeo, 2001: Figs. 1 View Fig , 2 View Fig ).

Compared to T. vietnamicum , the new species can be distinguished by the following characteristics: anterolateral margins of carapace very weakly serrate; epibranchial tooth very small and low but distinct; ambulatory legs slender,

RAFFLES BULLETIN OF ZOOLOGY 2017

merus of fourth pair leg about 5.6 times longer than broad; terminal segment of G1 curves inward (vs. anterolateral margins of carapace very weakly smooth; epibranchial tooth relatively much weaker and sometimes even absent; ambulatory legs stouter, merus of fourth pair leg about 5.1; terminal segment of G1 curves outward) ( Figs. 2 View Fig A–D, 4A–D; cf. Shih & Do, 2014: Fig. 6 View Fig ; Dang & Ho, 2012: Fig. 78).

This species can be distinguished from T. hamyen , new species, by some characteristics including ambulatory legs stouter, merus of fourth pair leg about 5.6 times longer than broad; terminal segment of G1 curves inward (vs. ambulatory legs slender, merus of fourth pair leg about 4.1 times longer than broad; terminal segment of G1 curves outward). ( Figs. 2A View Fig , 3B View Fig , 4 View Fig A–D, 5A, 6B, 7A–D).

This new species can be distinguished from T. vixuyenense by characteristics such as ambulatory legs stouter; G1 slender, sinuous (vs. ambulatory legs more slender; G1 conspicuously short, stout, straight). ( Figs. 2A View Fig , 4 View Fig A–D; cf. Shih & Do, 2014: Figs. 3 View Fig , 4 View Fig ).

Tiwaripotamon xuanson can be easily separated from other Tiwaripotamon species by the absent of dorsal flap in the terminal segment of the G1 (vs. dorsal flap present in T. edostilus (cf. Ng & Yeo, 2001: Fig. 5 View Fig ), T. pingguoense (cf. Dai & Naiyanetr, 1994: Fig. 1 View Fig ), T. pluviosum (cf. Do et al., 2016: Fig. 2 View Fig ), and T. xiurenense (cf. cf. Dai & Naiyanetr, 1994: Fig. 2 View Fig ).