Tayninhon, Dang & Tien & Tu, 2025

Tayninhon View in CoL gen. nov.

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Type species. Tayninhon nuibaden View in CoL gen. nov., sp. nov., by present designation.

Diagnosis. Carapace medium in size ( 13.7–26.5 mm, n = 12), subquadrate, dorsal surface relatively flat, rugae and striae on branchial and metabranchial regions; external orbital angle broadly triangular; epigastric and postorbital cristae low, rounded, distinctly separated by short groove; epistome with posterior margin acutely triangular at median, each lateral margin with two concavities; epibranchial tooth low with shallow notch; concavity between frontal margins broad, shallow; anterolateral margin weakly serrated; H-shaped grove well developed ( Fig. 1A–D View FIGURE 1 ). Exopod of third maxillipeds reaching beyond upper edge of ischium with well-developed flagellum ( Fig. 1E View FIGURE 1 ). Fingers of adult male major chela with almost no gap when closed ( Fig. 2A View FIGURE 2 ); ambulatory legs not elongated, third pair longest, first pair shortest; ratio of length to width of fourth merus less than 4 ( Fig. 1A, B View FIGURE 1 ). Sternopleonal cavity reaching to imaginary line connecting anterior edges of cheliped coxae ( Figs. 2C View FIGURE 2 , 3A View FIGURE 3 ). Thoracic sternum relatively wide; sternites 3 and 4 completely fused, separated by shallow oblique grooves; sternite 8 not visible when pleon closed ( Figs. 1B View FIGURE 1 , 2C View FIGURE 2 ). Telson triangular, relatively narrow, lateral margins concave ( Fig. 2D View FIGURE 2 ). G1 subterminal segment relatively broad; G1 terminal article slender, hook shape, with dorsal fold extending at basal part of terminal article, curved inwards ( Figs. 3A View FIGURE 3 , 4A–D View FIGURE 4 ). G2 slightly shorter than G1, distal article shorter than basal article. Vulvae oblique in position, proximal margin of each just touching suture with sternite 5 ( Fig. 4E, F View FIGURE 4 ).

Etymology. The genus is named after the location, the province of Tay Ninh, in combination with the genus name Potamon . The gender is neuter.

Remarks. Tayninhon gen. nov. is morphologically closest to Demanietta Bott, 1966 , in the shape of the carapace and the presence of a dorsal flap on the terminal segment of the first gonopod but is easily distinguished by the following characteristics: (1) the carapace size is smaller, the largest specimen is 26.5 mm in width (versus CW 27.7–62.8 mm of Demanietta see Rathbun 1904, 1905; Naiyanetr 1986; Yeo et al. 1999; Ng 2018; Shi et al. 2020; Lheknim et al. 2023; Tan et al. 2024); (2) sternopleonal cavity reaches to imaginary line connecting anterior edges of cheliped coxae ( Figs. 1B View FIGURE 1 , 2C View FIGURE 2 ) (versus sternopleonal cavity reaches to imaginary line connecting median points of cheliped coxae in Demanietta ; see Yeo et al. 1999: fig. 1F; Lheknim et al. 2023: fig.4C); and (3) G1 terminal article is bent and curving inwards with dorsal fold present only along the proximal part ( Figs. 3A View FIGURE 3 , 4A–D View FIGURE 4 ) (versus G1 terminal article bent and curving outwards with dorsal fold extending across the middle part in Demanietta ; see Tan et al. 2024: fig. 4D).

According to Yeo et al. (1999), almost all species of Demanietta were collected from fast-flowing mountain streams, waterfalls and cascades. However, the habitats of the new genus are more terrestrial. The holotype specimen was collected in an area without water, this individual appeared after heavy rain, crawling on large rocks.

Tayninhon View in CoL gen. nov. resembles Thaiphusa View in CoL somewhat in the form of the G1, but the new genus can be distinguished by the following characters: (1) the carapace is relatively flat and all regions are well defined ( Fig. 1A View FIGURE 1 ) (versus the carapace is distinctly swollen and all regions are smooth in Thaiphusa View in CoL ; e.g., see Ng & Naiyanetr 1993: fig. 22); (2) the anterolateral margins are serrated and cristae ( Fig. 1A View FIGURE 1 ) (versus the anterolateral margins are almost smooth and cristae very low; e.g., see Ng & Naiyanetr 1993: fig. 22); (3) the epigastric cristae are distinctly separated from the postorbital cristae ( Fig. 1A View FIGURE 1 ) (versus epigastric cristae are not distinctly separated from postorbital cristae; e.g., see Ng & Naiyanetr 1993: fig. 22); and (4) the terminal segment is about 0.4 times the length of the subterminal article with the dorsal fold prominent only along the proximal part of the terminal article ( Figs. 3A View FIGURE 3 , 4A–D View FIGURE 4 ) (versus terminal article is about 0.63 times length of subterminal article; and with the dorsal fold extends to the median part of terminal article; e.g., see Ng & Naiyanetr 1993: fig. 56).