Aiyunamon Pan, Ng & Sun, 2022

Ng, Peter K. L. & Tri, Ngo Van, 2023, Two new species of semiaquatic freshwater crabs of the genera Tortomon and Aiyunamon from karst forests in northern Vietnam (Crustacea: Brachyura: Potamidae), Zootaxa 5284 (2), pp. 364-376 : 369-370

Genus Aiyunamon Pan, Ng & Sun, 2022

Type species. Eosamon daiae Zhang & Sun in Zhang, Pan, Hao & Sun, 2020, by original designation.

Remarks. Pan et al. (2022) recently argued that four potamid species in China and Myanmar, which had previously been placed in Eosamon Yeo & Ng, 2007 , should be referred to a new genus, Aiyunamon : A. daiae (Zhang & Sun in Zhang, Pan, Hao & Sun, 2020), A. lushuiense ( Dai & Chen, 1985) , A. tengchongense ( Dai & Chen, 1985) and A. tumidum ( Wood-Mason, 1871) . Pan et al. (2023) subsequently showed that A. tumidum was a species complex and described a new species from southern China. We here add one new species from Vietnam, the first record of the genus from the country.

Pan et al. (2022: 323) separated Aiyunamon from Eosamon by its postorbital cristae being rugose and lower (versus not sharp and prominent), the external orbital tooth is low and is just separated from the anterolateral margin by shallow cleft (versus external orbital tooth prominent, and separated by a distinct cleft, the epibranchial tooth is low and sometimes barely visible indistinct (versus epibranchial tooth well-developed and sharp, the lateral margins of the male pleon are more or less straight or gently convex (versus male pleon lateral margins slightly concave to sometimes straight), the outer margin of the G1 at the junction of the two segments is distinctly concave (versus margin gently concave), the G1 terminal segment dose not have a visible dorsal flap in ventral view (versus with low, broad dorsal flap), and the anterior margin of the vulva is appressed on the suture of thoracic sternites 5/6, without a clear vulvar cover (versus anterior edge of vulva touching suture of thoracic sternites 5/6, with distinct vulvar cover). Ng & Clark (2022), in describing a new species of Eosamon from Cambodia, noted that the shape of the lateral margins of the male pleon is not taxonomically reliable. The dorsal flap on the G1 terminal segment is an indicative character but may not be always reliable as well. In Eosamon species, the dorsal flap on the G1 terminal segment is always wide and distinct, being clearly visible usually from the ventral perspective ( Yeo & Ng 2007: fig. 5; Yeo 2010: fig. 2; Ng & Clark 2022: fig. 3A–C). In Aiyunamon species, there is no obvious flap or only a low or small one is present; in A. vietnamicum n. sp., there is a low and wide flap when viewed dorsally ( Fig. 9C ) although when viewed ventrally, there is no obvious flap ( Fig. 9A, B ).

Figures

FIGURE 9. Aiyunamon vietnamicum n. sp., holotype male (21.5 × 17.5 mm) (ZRC 2022.790), Vietnam. A, left G1 (ventral view); B, distal part of left G1 (ventral view); C, distal part of left G1 (dorsal view); D, left G2. Scales: A, D = 1.0 mm; B, C = 0.5 mm.