Tuesday, August 9, 2016

[Crustacea • 2016] Tiwaripotamon pluviosum • A New Species of Freshwater Crab of the Genus Tiwaripotamon Bott, 1970 (Brachyura, Potamidae) from northern Vietnam and southern China

Tiwaripotamon pluviosum 
Do, Shih & Huang, 2016

 A new freshwater crab species of the family Potamidae is described from the boundaries of northern Vietnam and southern China. Tiwaripotamon pluviosum sp. nov. can be distinguished from other species by a suite of morphological characters, including a relatively flat carapace, relatively less slender legs, and distinct dorsal flaps on the male first gonopods. Molecular data using the mitochondrial cytochrome oxidase subunit I (COI) also supports this species as being new.

Key words: Tiwaripotamon pluviosum, taxonomy, mitochondrial DNA, cytochrome oxidase subunit I, COI

Fig. 5. Tiwaripotamon pluviosum sp. nov., male (CW 39.8 mm, SYSU 001205).
 A, dorsal view; B, frontal view;
G, H, a habitat in Duc Quang Commune, Ha Lang District, Cao Bang Province, Vietnam. 


Family Potamidae Ortmann, 1896
Subfamily Potamiscinae Ortmann, 1896 (sensu Yeo & Ng, 2003)

Genus Tiwaripotamon Bott, 1970
Type species: Geothelphusa annamensis Balss, 1914, by original designation.

Tiwaripotamon pluviosum sp. nov

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.

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

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 G1 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).

Van Tu Do, Hsi-Te Shih and Chao Huang. 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: 187–193.