Bioacoustics of Chinapotamon pusillum

Remarks. Examined specimens have characters agreeing well with Chinapotamon pusillum ( Song, 1984 ) . The species are characterized by: the small body size; the carapace dorsal surface being gently convex; the relatively distinct epigastric and postfrontal cristae ( Fig. 4A, B ); the quadrate ischium of third maxilliped, about 1.5 times longer than broad ( Fig. 4C ); there is almost no gap when the fingers of male major chela closes ( Fig. 4D ); the broadly rectangular male pleonal somite sixth, width to length ratio is 1.9 ( Fig. 5A ); the G1 is relatively slender, terminal segment directed upwards ( Fig. 5B ). Our specimens displayed some differences when compared to the descriptions of this species in Dai & Naiyanetr (1994) , Dai (1999) , Ng (2017) and Zou et al. (2018) : the anterolateral crista is low ( Figs. 4A, B ) (vs. the anterolateral crista is distinct; cf. Dai, 1999 : pl. IV, fig. 4; Ng, 2017 : table 1; Zou et al ., 2018 : table 2); G1 does not exceed the suture of sternites 4 and 5 ( Fig 5A ) (vs. G1 exceeds the suture of sternites 4 and 5; cf. Dai & Naiyanetr 1994 : Fig. 10.4 ; Dai 1999 : Fig. 42.4). The live colouration is overall brown in the specimens collected from Vietnam ( Fig. 10B ).

Remarks. The discovery of Chinapotamon pusillum ( Song, 1984 ) , in northern Vietnam may not come as a surprise, especially considering the similar geography of the area, with China . The Vietnamese specimens were collected from Dong Van Commune, Binh Lieu District, Quang Ninh Province , Vietnam , an area directly bordering Fangcheng District, Guangxi Province , southern China , which is the type locality of C. pusillum (Fig. 15 ). The two areas are part of a contiguous mountain range known as Shiwan Mountain ( Hu et al. 2023 ); it is very possible that the species is distributed throughout the range. Differences between C. pusillum ( Song, 1984 ) and its closest congener, C. insulare , have been discussed in detail in Le et al. (2024) . However, Le et al. (2024) treated specimens from Vietnam as C. cf. pusillum because they noted that they differed from the type description and figures in possessing more distinct anterolateral crista and a longer G 1 terminal article that reaches to beyond the suture between thoracic sternites 4 and 5. We obtained fresh photographs of the holotype of C. pusillum (Fig. 10 ) and we can now confirm that there are no obvious differences in the strength of the anterolateral cristae (Fig. 6 A ). The difference noted in how far the G 1 terminal article reaches beyond the suture between thoracic sternites 4 and 5 (Fig. 7 B ) can be affected by how much the male pleon is opened and flexed as well as the state of preservation of the specimens. Unfortunately, this is not apparent from the recent photographs of the holotype male. As such, we can only rely on the figure of this condition in Dai (1999 : fig. 42.4) which may not have been drawn accurately. Nevertheless, on the basis of the available morphological characters and close geographical proximity, we are now confident they are actually conspecific with C. pusillum ( Song, 1984 ) s. str. (Figs 6 – 8 , 10 , 15 ). Morphologically, C. pusillum ( Song, 1984 ) and C. insulare Le, Dang & Do, 2024 , are quite distinct compared to congeners. These two species have a carapace that is more subquadrate and G 1 terminal articles are directed more vertically, whereas in C. depressum ( Dai, Song, Li & Liang, 1980 ) , C. anglongense Dai & Naiyanetr, 1994 , C. clarkei Ng, 2017 , C. dashiwei Ng, 2017 , C. glabrum ( Dai, Song, Li & Liang, 1980 ) , C. halangense sp. nov. , C. longlinense Dai & Naiyanetr, 1994 , C. maolanense Zou, Bai & Zhou, 2018 and C. xingrenense Dai & Naiyanetr, 1994 , the carapace is more transversely subovate and the G 1 terminal article is distinctively bent outwards (Figs 1 , 5 , 6 , 10 ; cf. Ng 2017 : figs 2, 6, 8; Zou et al. 2018 : fig. 7, table 2). For now, C. pusillum and C. insulare will be retained in the genus Chinapotamon until the genus can be revised.