Bioacoustics of Indochinamon frontatum

Remarks. The genus Indochinamon was established by Yeo & Ng (2007) for Indochinese species previously placed in Potamon Savigny, 1816 s. l. , and defined by the G1 terminal segment being relatively short and stout, with the groove for the G2 marginal in position. The carapace characters are very similar in most Indochinamon species : carapace low, with relatively flat dorsal surface; epigastric cristae separated from postorbital cristae by distinct groove; and the postorbital cristae not confluent with the epibranchial tooth. However, the morphological differences of the G1 terminal segments among the species in this genus can be very significant. Thus, Ng & Win Mar (2018) separated Indochinamon into four main groups by the morphological characters of the G1 terminal segments: 1) short and stout, gently bent; 2) slender, elongate, and straight; 3) curved; and 4) strongly bent. The G1 of new species closely resembles that of the curved G1 group (group 3). In this group, the new species is likely to be confused with I. malipoense Zhang & Sun in Zhang, Pan, Hao & Sun, 2020 , as the G1 terminal segment gently bent outwards and curving. However, the new species can be distinguished by the following combination of diagnostic morphological characters: the frontal region of carapace with prominently cristae in median position just behind of frontal margin ( Fig. 2A ) (versus the incomplete cristae or rugosity just behind the frontal margin); the G1 terminal segment is prominently hooked and bent at about 45° outward, and the dorsal flap with low, broadly rounded apex medial in position ( Figs. 5A–D , 6A, B ) (versus the G1 terminal segment is slightly hooked and bent at about 30° outward, and the dorsal flap with rounded apex proximal in position) (cf. Zhang, Pan, Hao & Sun 2020 : I. malipoense figs. 7B, 8B, C, F, 10A). The new species is also superficially similar to I. ahkense Naruse, Chia, & Zhou, 2018 in this group, but can be further distinguished by a unique combination of the curved G1 terminal segment and the higher dorsal flap exceeding inner margin (versus the relatively straight G1 terminal segment with the lower dorsal flap not exceeding inner margin) (cf. Naruse, Chia & Zhou, 2018 : I. ahkense fig. 4). The new species is externally differentiated from the strongly curved G1 group (group 4), such as I. boshanense ( Dai & Chen, 1985 ) , I. flexum ( Dai, Song, Li & Liang, 1980 ) , and I. dangi Naruse, Nguyen & Yeo, 2011 , by the the G1 terminal segment being slender, more strongly hooked, and gently tapering distally ( Figs. 5A–D , 6A, B ) (versus the G1 terminal segment is stout, relatively straight, with inflated proximal part) (cf. Dai 1999 : I. boshanense , fig. 96, I. flexum fig. 97; Naruse, Nguyen & Yeo, 2011 : I. dangi , fig. 9d, 9e). The new species is different from most of the congeners in having distinctly convex cristae on the frontal region, at least based on the series of six specimens on hand which includes adults and juveniles. We regard this as a diagnostic character for I. frontatum sp. nov.