Tiwaripotamon pluviosum, Do & Shih & Huang, 2016

Do, Van Tu, Shih, Hsi-Te & Huang, Chao, 2016, A new species of freshwater crab of the genus Tiwaripotamon Bott, 1970 (Crustacea, Brachyura, Potamidae) from northern Vietnam and southern China, Raffles Bulletin of Zoology 64, pp. 213-219 : 214-218

Tiwaripotamon pluviosum sp. nov.

( Figs. 1–6 )

Material examined. Holotype: male (32.2 × 23.2 mm) ( 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 . Paratypes: 1 male (23.3 × 18.8 mm) ( IEBR-FC TPx02) , 2 females (29.7 × 22.1, 16.9 × 13.5 mm) ( IEBR-FC TPx03, IEBR-FC TPx04) ; 1 male (21.7 × 17.1 mm), 1 female (32.7 × 25.3 mm) (NCHUZOOL 14786); 1 male (21.0 × 16.3 mm), 1 female (16.7 × 13.1 mm) ( ZRC 2015.0482 ), same data as holotype . Other material: male (39.8 × 28.8 mm) ( SYSU 001205 ), Nonggang Natural Reserve , Longzhou County, Chongzuo City, Guangxi Province, China, coll. local collector, August 2013 .

Comparative material. Tiwaripotamon edostilus Ng & Yeo, 2001: 1 male (26.1 × 21.4 mm), ( IEBR-FC TE01 ), Cat Ba Island , Hai Phong City, Vietnam, 15–170 m, coll. V. T. Do, 18–19 March 2013. T. pingguoense Dai & Naiyanetr, 1994 : female (42.2 × 32.6 mm) ( SYSU 001166 ), Pingguo County, Baise City , Guangxi Province, China, coll. local collector, September 2013 . T. vietnamicum (Dang & Ho, 2002) : 2 males (44.5× 32.8 mm, 41.3× 31.2 mm), ( IEBR-FC TVn01, NCHUZOOL 13612), Cuc Phuong National Park , Ninh Binh Province, Vietnam, 500 m, coll. V. T. Do, 14 May 2013 . T. vixuyenense Shih & Do, 2014: 1 male (26.4 × 20.5 mm) ( 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 . T. xiurenense Dai & Naiyanetr, 1994: 1 male (39.6 × 29.7 mm) (NCHUZOOL 13610), Lipu , Guangxi, China, coll. local collector, 18 May 2009 .

Diagnosis. Carapace about 1.3 times broader than long; transverse, low; dorsal surface relatively flat; glabrous; regions poorly defined, cervical groves shallow; H-shaped depression shallow but distinct. Epigastric cristae distinct; postorbital cristae rounded, confluent with epibranchial tooth. External orbital angle triangular, outer margin gently convex; epibranchial tooth small, broadly triangular, separated from external orbital angle by distinct, broadly triangular cleft. Ambulatory legs less slender; fourth pair with length of merus about 4.7 times width. G1 terminal segment distinctly upcurved, with distinct dorsal flap in proximal part.

Description. Carapace ( Figs. 1A , 3A , 4A , 5A ) about 1.3 times broader than long (n = 8). Epigastric cristae rugose, separated by narrow, shallow groove that opens up into inverted V-shape posteriorly; postorbital cristae rugose, rounded, low, confluent with epibranchial tooth; regions behind epigastric and postorbital cristae weakly rugose. Frontal margin broadly emarginated medially; frontal region deflexed, appearing relatively narrow from dorsal view, smooth; supra-and infraorbital margins distinctly cristate, supraorbital margins sinous, infraorbital margin arched; orbital region smooth, relative narrow; eyes normal with no adaptations to cave environments. External orbital angle sharply triangular, outer margin slightly convex; epibranchial tooth small, broadly triangular, separated from external orbital angle by distinct broadly triangular cleft; anterolateral margin convex, serrated in upper part; metabranchial regions smooth.

Ischium of third maxilliped ( Fig. 1C ) quadrate, about 1.2–1.5 times longer than broad, with shallow longitudinal median sulcus; exopod with short but distinct flagellum, about 1/2 of merus width (n = 4).

Chelipeds ( Figs. 3A, C , 4A, C , 5A , 6 ) subequal, with outer surface smooth. Right cheliped large in holotype, with length of palm+pollex about 2.8 times palm height. Ambulatory legs ( Figs. 3A , 4A , 5A ) smooth, less slender; all dactylus and propodus with prominent spines in both upper and lower margins; second leg with dactylus about 9.1 times longer than proximal width, propodus about 5.6 times longer than broad and about 1.1 times longer than dactylus, carpus about 0.7 times length of dactylus, merus about 1.6 times longer than dactylus (n = 3); fourth leg with dactylus about 9.5 times longer than proximal width, propodus about 1.0 times length of dactylus; carpus about 0.6 times length of dactylus (n = 3), merus about 4.8 times longer than proximal width (n = 7) and about 1.3 times longer than dactylus (n = 3).

Male abdomen ( Figs. 1B , 3C , 5C ) broadly triangular, with proximal width of sixth segment about 2.8 times length; telson broadly triangular, tip rounded, with proximal width about 1.4 times length (n = 4).

Suture ( Figs. 3C , 5C, D ) between thoracic sternites 2 and 3 complete, distinct; groove between sternites 3 and 4 present; thoracic sternites 5 and 6 interrupted medially; sternites 7 and 8 medially separated by distinct longitudinal median suture ( Fig. 5E, F ). Male abdominal cavity reaching beyond imaginary line joining the base of the chelipeds. Tubercles of male abdominal-locking mechanism positioned in thoracic sternite 5.

G1 ( Fig. 2 A–F) relatively short; terminal segment distinctly upcurved, about 0.34 times length of subterminal segment, about 3.0 times longer than proximal width, with distal opening subventral in position. G2 ( Fig. 2G ) about 1.2 times longer than G1, distal segment well developed, about 0.5 times as long as basal segment ( Fig. 3I, J ). Female gonopore ( Fig. 5E, F ) in thoracic sternite 6, ovate, without operculum, opened posteromesially; anterioexternal margin partially covered by a raised rim; posteromesial margin surrounded by a low raised rim.

Etymology. The name “ pluviosum ” means rainy, which refers to the specimens being collected and active during the rainy season.

Live coloration. Various from reddish brown, purple to orange ( Figs. 3 , 4 , 5A, B , 6 ).

Ecological notes. This species inhabits limestone mountains ( Fig. 5G, H ), and are most active during the rainy season (personal observation). Similar to T. vixuyenense (cf. Shih & Do, 2014), specimens of this species were also found crawling on the leaves and twigs, with one specimen observed being one metre above the ground at night.

Remarks. This species fits well within the character descriptions of Tiwaripotamon defined by Ng & Yeo (2001) due to the squarish third maxilliped ischium, short third maxilliped exopod with a short flagellum, slender legs, broadly triangular male abdomen, and an upcurved G1 terminal segment ( Figs. 1–4 ). This new species can be separated from other congeners (see below) by the relatively flat and transverse dorsal surface of the carapace, proportionately stouter ambulatory legs and distinct dorsal flap on the G1.

The G1 of this species resembles T. edostilus in the presence of a dorsal flap, but it is smaller in size in the latter (versus larger in this species) ( Fig. 2 ; cf. Ng & Yeo, 2001: fig. 5). The new species can also be separated from T. edostilus by the flatter and more transverse carapace (ratios of CW: CL is 1.3 of this species; 1.2 of T. edostilus ; cf. Shih & Do, 2014) and stouter ambulatory legs (see below). The carapace of the new species is similar with T. annamense in the morphology of the anterolateral margin. However, the two can be easily separated by the presence of a dorsal flap on the G 1 in the former ( Fig. 2 ) and the absence of such in the latter ( Ng & Yeo, 2001: fig. 2D–I). The merus of the fourth ambulatory leg is about 4.8 times longer than broad for this species, which is shorter than most congeners: 6.5 for T. vixuyenense , 5.1 times for T. vietnamicum , 5.6 times for large T. edostilus specimens and 5.3 times for T. xiurenense (unpublished data; Shih & Do, 2014), but longer than T. pingguoense (4.3 times, unpublished data) and T. annamense (approximately 4.5 times, estimation derived from dactylus ratio, Ng & Yeo, 2001).

DNA results and discussion. The pairwise K2P-corrected genetic distances between species for COI are shown in Table 2. The minimum interspecific divergence between T. pluviosum sp. nov. and other species of Tiwaripotamon is 6.22%, which is large enough to support this species genetically (see below). This value is larger than the minimum interspecific K2P distances of other potamid crabs which have closely related species pairs, e.g., Geothelphusa (3.17% between G. tali Shy, Ng & Yu, 1994 and G. minei Shy & Ng, 1998 , recalculated from Shih et al. (2011a); 2.83% between G. candidiensis Bott, 1967 and G. olea Shy, Ng & Yu, 1994 , re-calculated from Shih et al. (2008)), Nanhaipotamon (2.17% between N. nanriense Dai, 1997 and N. dongyinense Shih, Chen & Wang, 2005 , re-calculated from Shih et al. (2011b)) and Longpotamon (= Sinopotamon , see Shih et al., 2016) (1.8% between L. shanxianense ( Dai & Chen, 1981) and L. tongbaiense ( Dai & Chen, 1981) of the L. yangtsekiense ( Bott, 1967) complex, Zheng et al., 2006),

.

)

parentheses

in vixuyenense

given T.

values) maximum vietnamicum 13.81 12.66 – (and. T 13.24 minimum () 10.88 12.51)

Tiwaripotamon . T

edostilus (10.87 – 10.86 12.33 12.15 – (of

species

Interspecific

)

) 9.78

)

13.02 six xiurenense 7.38 (– 7.2 (9.77 – 11.83 – (between. T 7.29 9.77 12.42 and

within sequences pingguoense 6.11 6.9 6.73 –) 7.07) 10.5 10.47 – (– 11.75

) (13.23.

(

COI T 10.48 12.49 the)) on based) 6.9 – –) 8.27 8.62) 11.93 – 14.15 – pluviosum (6.22 6.81 ((– 7.4 (10.47 (12.28 percent T. 6.45 7.36 7.95 11.04 13.27 in distances

pairwise

genetic

Intraspecific divergence Nucleotide () 3.18 – 0.15 5.25 — — % 0.30 % 0.31 1.86 % P-corrected

2

.

Mean

K

2 pluviosum pingguoense xiurenense edostilus vietnamicum vixuyenense

Table T.. T T.. T T.. T

although it is slightly smaller than Johora (6.70% between J. grallator Ng, 1988 and J. gua Yeo, 2001 , re-calculated from Yeo et al. (2007), excluding the possible conspecifics). In addition, although the intraspecific divergence is large from the nine specimens (mean: 3.18%; maximum: 5.25%), no further subdivision was found (phylogenetic tree not shown), which may be due to the wide distribution of T. pluviosum in the boundary region between Vietnam and China, with different degrees of geographical barriers.

Figures

Fig. 1. Tiwaripotamon pluviosum sp. nov., holotype (CW 32.2 mm, IEBR-FC TTx01). A, carapace, dorsal view; B, abdominal somites 3–6 and telson; C, right third maxilliped.

Fig. 2. Tiwaripotamon pluviosum sp. nov., holotype (CW 32.2 mm, IEBR-FC TTx01). A–F, left G1: A, ventral view; B, ventral view of terminal segment; C, dorsal view; D, dorsal view of terminal segment; E, mesial view; F, mesial view of terminal segment. G, right G2.

Fig. 3. Tiwaripotamon pluviosum sp. nov., holotype (CW 32.2 mm, IEBR-FC TTx01). A, dorsal view; B, frontal view; C, ventral view.

Fig. 4. Tiwaripotamon pluviosum sp. nov., paratype, female (CW 32.7 mm, NCHUZOOL 14786). A, dorsal view; B, frontal view; C, ventral view.

Fig. 5. Tiwaripotamon pluviosum sp. nov. A–D, male (CW 39.8 mm, SYSU 001205). A, dorsal view; B, frontal view; C, D, ventral view. E, F, female right gonopore (CW 32.7 mm, NCHUZOOL 14786). G, H, a habitat in Duc Quang Commune, Ha Lang District, Cao Bang Province, Vietnam.

Fig. 6. A, B, Tiwaripotamon pluviosum sp. nov., live coloration. Photos taken from Nonggang Natural Reserve, Longzhou County, Chongzuo City, Guangxi Province, China.Specimens not collected (courtesy of Heng-Wei He).