Taxonomic notes on three species of Tiwaripotamon Bott, 1970 (Crustacea: Brachyura: Potamidae) from Vietnam and China, one of which is new to science Author Ng, Peter K. L. text Zootaxa 2024 2024-07-04 5476 1 298 313 http://dx.doi.org/10.11646/zootaxa.5476.1.24 journal article 10.11646/zootaxa.5476.1.24 1175-5326 12681699 880763E8-5AE7-4F9C-AB40-EC5FC386E052 Tiwaripotamon xiurenense Dai & Naiyanetr, 1994 ( Figs. 9–12 ) Material examined. Holotype : male (48.6 × 34.1 mm ) ( ZRC 2020.169 ), Xiuren County , Guangxi Zhuang Autonomous Region , China , coll. 15 February 1938 . Paratype : 1 female (29.7 × 23.1 mm ) ( CAS-CB 5197 ), same data as holotype. Others : 1 male (39.7 × 29.5 mm ) (NCHUZOOL 18610), Lipu , Guangxi , southern China , coll. 18 May 2009 . Diagnosis. Carapace subquadrate, distinctly wider than long ( Figs. 9A, B , 10A ); epigastric cristae very low, postorbital cristae not visible ( Figs. 9A, B , 10A ); external orbital tooth acutely triangular, distinct, outer margin gently convex to distinctly concave, separated from anterolateral margin by cleft ( Figs. 9A, B , 10A ); epibranchial tooth small sharp, rest of anterolateral margin subcristate, almost smooth, entire ( Figs. 9A, B , 10A ); suborbital margin convex, smooth, without inner tooth; suborbital region smooth, subhepatic, pterygostomial and sub-branchial regions weakly rugose to smooth ( Figs. 10F, H ); posterior margin of epistome with low, wide median lobe, broadly triangular ( Fig. 10B, H ). Male thoracic sternites punctate ( Figs. 10F ); tubercle of male pleonal locking mechanism on posterior third of somite 5 ( Dai 1999 : fig. 185-3). Ambulatory legs very long ( Figs. 9 , 11B, C ). Male pleon is quadrate, somites 3 and 4 very wide ( Fig. 10F, G ). G1 with subterminal segment gently curved outwards, outer margin gently concave; terminal segment long, sharply tapering, distinctly upcurved, basal part with low rounded lobe ( Figs. 12A–F ). Vulva large, ovate, opening subtriangular, directed obliquely inwards, occupying most of sternite 6, gently pressing onto the suture with sternite 5 ( Fig. 11D ). Females and variation. The female paratype is smaller than the holotype male and the carapace is quite different in appearance. Compared to the male ( Fig. 9A ), its carapace is distinctly more quadrate, proportionally narrower with the branchial regions less swollen, the external orbital tooth is less acute with the outer margin gently convex and the epibranchial tooth is not sharp ( Fig. 9B ). As with most potamids, the female chelae are relatively smaller and the major chela is not inflated and enlarged ( Fig. 9B versus Figs. 9A , 11A ). Remarks. Among the many specimens of Chinese crabs donated to the ZRC in the 1990s as part of an exchange of material with the late Prof Dai Ai-Yun was a specimen of Tiwaripotamon xiurenense . It was not labelled as a type and has been placed in the main shelves of the ZRC since the exchange. A re-examination of this specimen shows that it is actually the holotype male described and figured by Dai & Naiyanetr (1994) , agreeing in all details, including the measurements. It is here re-catalogued as the holotype of the species. This also explains why Ng Ngan Kee, Zhou Xianmin and Tohru Naruse could not locate the holotype of the species when they photographed the types of freshwater crabs in CAS; and only the paratype female was found ( Fig. 9B ). A smaller male (39.7 × 29.5 mm , NCHUZOOL 18610), collected from Lipu in Guangxi , is also here identified with T. xiurenense ; its carapace features and G1 structure agree very well with the holotype male. FIGURE 9. Tiwaripotamon xiurenense Dai & Naiyanetr, 1994 , overall dorsal habitus. A, holotype male (48.6 × 34.1 mm) (ZRC 2020.169), China; B, paratype female (29.7 × 23.1 mm) (CAS-CB 5197), China It is important to note that the G1 as depicted in the original figure of the species ( Dai & Naiyanetr 1994 : fig. 2-4, 2-5; Dai 1999 : fig. 185-4, 185-5) is drawn tilted to one side. In these figures, the G1 subterminal segment is slender, the terminal segment is very long and slender, and there is a small basal dorsal flap visible in the ventral and dorsal views (see Fig. 12B, E ). When the G1 is viewed with the lateral surfaces horizontal and centred (standard orientation for freshwater crab figures), however, the structure looks very different, with the subterminal segment much wider, the terminal segment is relatively shorter and the basal dorsal flap is not visible in the ventral or dorsal views ( Fig. 12A, C, D, F ). The very different appearance of the G1 when figured from different perspectives is a factor that must be considered when comparisons with allied taxa are made. Previous papers describing species of Tiwaripotamon have relied primarily on the original figures by Dai & Naiyanetr (1994) and Dai (1999) for T. xiurenense and T. pingguoense , so these comparisons are not completely reliable (e.g., Yeo & Ng 2001 ; Do et al. 2017 ).