Aiyunamon, Pan & Ng & Sun, 2022

Pan, Da, Ng, Peter K. L. & Sun, Hongying, 2022, Aiyunamon, a new genus for southern Chinese potamid species previously placed in Eosamon Yeo & Ng, 2007 (Decapoda: Brachyura: Potamidae), Raffles Bulletin of Zoology 70, pp. 320-328 : 321-325

publication ID	https://doi.org/ 10.26107/RBZ-2022-0016
publication LSID	lsid:zoobank.org:pub:1E7D8362-E5CF-49F2-B4EA-778E67B5CC94
persistent identifier	https://treatment.plazi.org/id/CF07CA02-AB5B-4202-A230-7E01A2858D7B
taxon LSID	lsid:zoobank.org:act:CF07CA02-AB5B-4202-A230-7E01A2858D7B
treatment provided by	Felipe
scientific name	Aiyunamon
status	gen. nov.

Treatment

Aiyunamon View in CoL , new genus

Type species. Eosamon daiae Zhang & Sun, 2020 View in CoL , by present designation.

Material examined. Aiyunamon daiae ( Zhang & Sun, 2020) : 1 male (26.6 × 22.2 mm, NNU 190503 ) (holotype), Bangyang Village , Longba Town , Longchuan County, Dehong Prefecture, Yunnan Province, China, coll. X. Hao & Z. Zhang, 5 May 2019 ; 1 female (20.1 × 16.5 mm, NNU 190505 ) (paratype), same data as holotype. Aiyunamon lushuiense ( Dai & Chen, 1985) : 1 male (26.5 × 22.1 mm, NNU 148401 ), Wagu Village , Liuku Town, Lushui City, Yunnan Province, China, coll. K. Chu, P. Wang & H. Sun, 4 May 2016 ; 1 female (21.4 × 18.3 mm, NNU 282103 ), Shuishan Village , Lushui City, Yunnan Province, China, coll. K. Chu, P. Wang & H. Sun, 4 May 2016 . Aiyunamon tengchongense ( Dai & Chen, 1985) : 1 male (37.9 × 30.1 mm, NNU 193261 ), Lianghe County, Yunnan Province, China, coll. X. Hao & Z. Zhang, 9 May 2019 ; 1 female (25.5 × 20.5 mm, NNU 282202 ), Hongdoushu Village , Menglian County, Tengchong City, Yunnan Province, China, coll. K. Chu, P. Wang & H. Sun, 5 May 2016 . Aiyunamon tumidum ( Wood-Mason, 1871) : 1 male (23.2 × 18.7 mm, IZCAS CB11382 ), Sipai Mountain , Yunnan Province, China, coll. 1964 ; 1 female (23.6 × 18.4 mm, IZCAS CB11383 ), Sipai Mountain , Yunnan Province, China, coll. 1964. Eosamon smithianum ( Kemp, 1923) : 1 male (49.6 × 39.1 mm, ZRC 1990.498 View Materials – 514 View Materials ), 1 female (39.5 × 33.4 mm, ZRC 1990.498 View Materials – 514 View Materials ), Krating Waterfall area, near Kitchagood National Park, eastern Thailand, fast flowing water with smooth rocks, sand substrate, coll. P. K. L. Ng, December 1988 .

Diagnosis. Carapace slightly broader than long, dorsal surface slightly convex, regions distinctly defined; epigastric cristae distinct, rugose, separated from postorbital cristae by shallow groove; postorbital cristae distinct, rugose; H-shaped groove distinct ( Figs. 2A–D View Fig , 3A–D View Fig ). Frontal margin slightly sinuous, gently concave medially, placed anterior to level of external orbital angles; external orbital angle low, separated from rest of margin by small or shallow cleft; epibranchial tooth low, not prominent; anterolateral margins slightly convex, cristate, lined with distinct granules; posterolateral margins gently converging posteriorly ( Fig. 2A–D View Fig ). Third maxilliped exopod with long flagellum. Male pleon triangular, lateral margins almost straight ( Fig. 4A–D View Fig ). G1 curved outwards; distal part of outer margin of subterminal segment at junction with terminal segment deeply concave; terminal segment conical, straight to slightly curved, without dorsal flap ( Fig. 5A–D, F–I View Fig ); G2 slender. Female vulvae with anterior margin appressed against suture of thoracic sternites 5/6, ovate, without operculum ( Fig. 6A–D View Fig ).

Etymology. The genus is named after the late Prof. Aiyun Dai, in honour of her immense contributions to Chinese freshwater crab taxonomy. Gender of genus neuter.

Remarks. This new genus currently contains four species, Aiyunamon daiae ( Zhang & Sun, 2020) (type species), A. lushuiense ( Dai & Chen, 1985) , A. tengchongense ( Dai & Chen, 1985) , and A. tumidum ( Wood-Mason, 1871) .

Morphologically, Aiyunamon is most similar to Eosamon but can be separated by the following characters: postorbital cristae rugose ( Figs. 2A–D View Fig , 3A–D View Fig ) (versus postorbital cristae sharp in Eosamon ; Figs. 2E View Fig , 3E View Fig ; cf. Yeo & Ng, 2007: fig. 5); external orbital angle low, separated from the lateral margin by shallow cleft ( Figs. 2A–D View Fig , 3A–D View Fig ) (versus external orbital angle prominent, separated from lateral margin by deep cleft in Eosamon ; Figs. 2E View Fig , 3E View Fig ; cf. Yeo & Ng, 2007: fig. 5); epibranchial tooth indistinct ( Fig. 2A–D View Fig ) (versus epibranchial tooth distinct, sharp in Eosamon ; Fig. 2E View Fig ; cf. Yeo & Ng, 2007: fig. 5); male pleon lateral margins straight ( Fig. 4A–D View Fig ) (versus male pleon lateral margins slightly concave in Eosamon ; Fig. 4E View Fig ; cf. Yeo & Ng, 2007: fig. 5); G1 subterminal segment with distal part of outer margin, at junction with terminal segment, deeply concave ( Fig. 5A–D, F–I View Fig ) (versus G1 outer margin of subterminal segment gradually tapering to junction with terminal segment, margin appearing gently concave in Eosamon ; Fig. 5E, J View Fig ; cf. Yeo & Ng, 2007: fig. 5); G1 terminal segment without any trace of dorsal flap ( Fig. 5A–D, F–I View Fig ) (versus G1 terminal segment with low, broad dorsal flap in Eosamon ; Fig. 5E, J View Fig ; cf. Yeo & Ng, 2007: fig. 5); and anterior margin of female vulvae appressed on suture of thoracic sternites 5/6, without operculum ( Fig. 6A–D View Fig ) (versus only anterior edge of female vulvae touching suture of thoracic sternites 5/6, with distinct lateral operculum present in Eosamon ; Fig. 6E View Fig ).

Aiyunamon is also superficially similar to Indochinamon Yeo & Ng, 2007 which is also present in southwestern China. Aiyunamon can easily be distinguished by its proportionately less transverse carapace ( Fig. 2A–D View Fig ) (versus more transverse carapace in Indochinamon ; cf. Yeo & Ng, 1998: fig. 7D); the epigastric cristae being separated from postorbital cristae by shallow groove ( Fig. 2A–D View Fig ) (versus epigastric cristae being separated from postorbital cristae by distinct groove in Indochinamon ; cf. Yeo & Ng, 1998: fig. 7D; the external orbital angle is low and separated from the rest of the margin only by a shallow cleft ( Figs. 2A–D View Fig , 3A–D View Fig ) (versus well-developed external orbital angle separated from rest of margin by a deep cleft in Indochinamon ; cf. Yeo & Ng, 1998: fig. 7D); the low epibranchial teeth ( Fig. 2A–D View Fig ) (versus more distinct, sharp epibranchial teeth in Indochinamon ; cf. Yeo & Ng, 1998: fig. 7D) and relatively more slender G1 terminal segment ( Fig. 5A–D, F–I View Fig ) (versus relatively stouter terminal segment in Indochinamon ; cf. Yeo & Ng, 1998: fig. 5I, J). The carapace of Aiyunamon can be distinguished from Doimon Yeo & Ng, 2007 by the same suite of features as in Indochinamon (cf. Naiyanetr & Ng, 1990: fig. 4); and the G1 terminal segment is gently curved to straight and without any dorsal flap ( Fig. 5A–D, F–I View Fig ) (versus more curved terminal segment with a clear dorsal flap in Doimon ; cf. Naiyanetr & Ng, 1990: fig. 5A−C). Aiyunamon differs from Iomon Yeo & Ng, 2007 in having the external orbital angle low and separated from the rest of the margin only by a shallow cleft ( Fig. 2A–D View Fig ) (versus external orbital angle relatively large, broadly triangular in Iomon ; cf. Ng & Naiyanetr, 1993: fig. 13), and the G1 slightly bent outwards ( Fig. 5A–D, F–I View Fig ) (versus G1 distinctly bent outwards in Iomon ; cf. Ng & Naiyanetr, 1993: fig. 48).

In its external features, Aiyunamon is also superficially similar to Potamiscus montosus Dai , Song, He, Cao, Xu & Zhong, 1975, and P. yiwuensis Dai & Cai, 1998 . The new genus, however, is easily separated by possessing a distinct flagellum on the third maxilliped exopod (cf. Dai, 1999: figs. 91, 92, 93; Zhang et al., 2020: fig. 4) (versus absent or vestigial flagellum in Potamiscus ; cf. Dai & Cai, 1998: fig. 2; Dai, 1999: fig. 99) and the relatively slender G1 terminal segment ( Fig. 5A–D, F–I View Fig ) (versus relatively stouter G1 terminal segment in Potamiscus ; cf. Dai & Cai, 1998: figs. 5, 6; Dai, 1999: fig. 99).

The confirmed distribution of Aiyunamon is southwestern Yunnan ( Fig. 1 View Fig ), about 1,300 –1,700 m above sea level. Aiyunamon tumidum was described from Yunnan and upper Myanmar ( Wood-Mason, 1871: 454) but we are not certain if all his specimens belong to the same species; they will need to be re-examined. Yeo & Ng (2007: 304) recorded one syntype male and seven non-type specimens of A. tumidum in their revision of the Potamidae , but all were from Yunnan. Aiyunamon species are usually found hiding under stones and/or burrowing on the banks of shallow hilly streams, and they have also been found in holes on the ridges of rice fields. The burrows in the rice fields are about 30–50 cm deep.

The dispersal abilities and fecundity of freshwater crabs are relatively low. As such, genera usually do not have disjunct distributions, especially for highland taxa. Therefore, as exemplified by this study, genera with disjunct distributions should be restudied to see if the taxa are monophyletic. Another case is Tenuipotamon Dai, 1990 , which also has a disjunct distribution, but studies have since shown that the genus is not monophyletic (cf. Pan et al., 2022: figs. 2, 3).