Nanhaipotamon guangdongense Dai, 1997

Huang, Chao, Wong, Kai Chin & Ahyong, Shane T., 2018, The freshwater crabs of Macau, with the description of a new species of Nanhaipotamon Bott, 1968 and the redescription of Nanhaipotamonwupingense Cheng, Yang, Zhong & Li, 2003 (Crustacea, Decapoda, Potamidae), ZooKeys 810, pp. 91-111 : 98-100

Nanhaipotamon guangdongense Dai, 1997 Figs 2B, 6G, 7

Nanhaipotamon guangdongense Dai, 1997: 229, fig. 9; Dai 1999: 121, pl. 8(1), fig. 60; Huang et al. 2012: 57, fig. 1A, 60; fig. 4, 61; fig. 5 A–C.

Type material.

Holotype: AS-CB 05141, male (33.2 × 26.4 mm), Guangdong Province, China, gift from Sun Yat-Sen Medical College, no date [photographs examined].

Other material examined.

SYSU 001001, male (38.5 × 30.0 mm), Xiangzhou (22.25N, 113.57E), Zhuhai City, Guangdong, blue, mud hole next to small hillstream, coll. C. Huang, May 2012. SYSBM 001003, 1 male (36.2 × 28.4 mm), Xiangzhou, Zhuhai City, Guangdong, mud hole next to small hill stream, coll. C. Huang, February 2011. SYSBM 001004, 1 male (30.5 × 24.3 mm), Xiangzhou, Zhuhai City, Guangdong, mud hole next to small hill stream, coll. C. Huang, August 2012. SYSBM 001177, 1 male (35.4 × 29.4 mm), Xiangzhou, Zhuhai City, Guangdong, mud hole next to small hill stream, coll. C. Huang, May 2013. SYSBM 001178, 1 female, (35.9 × 29.4 mm), same data as above. SYSU 001758-001760, 3 males (40.1 × 32.7 mm, 36.0 × 29.8 mm, 30.2 × 25.1 mm), Xiangzhou, Zhuhai City, Guangdong, blue, mud hole next to small hillstream, coll. C. Huang, September 2018. SYSU 001761-001764, 4 males (42.1 × 33.5 mm, 40.5 × 32.4 mm, 38.1 × 32.0 mm, 32.5 × 27.0 mm), Xiangzhou, Zhuhai City, Guangdong, mud hole next to small hill stream, coll. C. Huang, September 2018. SYSBM 001141-001143, 3 males (38.4 × 31.5 mm, 40.8 × 32.2 mm, 36.7 × 29.4 mm), Gujing (22.36N, 113.12E), Jiangmen City, Guangdong, coll. local, August 2013. IACM, 2 males (39.5 × 31.5 mm, 25.2 × 21.1 mm), Taipa (22.16N, 113.58E), Macau, mud hole next to small hill stream, coll. K.C. Wong, March 2018. SYSBM 001645-001646, 2 males (35.9 × 28.8 mm, 30.9 × 24.8 mm), Taipa, Macau, mud hole next to small hill stream, coll. C. Huang, June 2018. SYSBM 001656, 1 male (45.5 × 37.0 mm), Dahengqin mountain (22.11N, 113.50E), Hengqin Island, Zhuhai City, Guangdong, in small hill stream pool, coll. C. Huang, August 2017. SYSBM 001672, 1 male (22.4 × 18.5 mm), Jinwan (22.08N, 113.35E), Zhuhai City, Guangdong, mud hole next to small hill stream, coll. C. Huang, June 2018. SYSBM 001673-001674, 2 females (31.7 × 25.7 mm, 25.9 × 20.8 mm), same data as above. SYSBM 001017-001019, 3 males (33.4 × 26.5 mm, 29.2 × 23.6 mm, 27.6 × 21.7 mm), Doumen (22.19N, 113.29E), Zhuhai City, Guangdong, coll. local, April 2013. SYSBM 001657-001658, 2 males (36.9 × 30.4 mm, 23.0 × 19.5 mm), Jinzhong Reservoir (22.48N, 113.38E), Zhongshan City, Guangdong, mud hole next to small hill stream, coll. C. Huang, January 2018. SYSBM 001659, 1 female (23.6 × 19.8), same data as above. SYSBM 001016, 1 male (40.5 × 33.1 mm), Qi’ao Island (22.43N, 113.66E), Zhuhai City, Guangdong, mud hole next to small hill stream, coll. C. Huang, May 2011. SYSBM 001023, 1 female (40.5 × 33.1 mm), same data as above. SYSBM 001750, 1 male (39.6 × 32.5 mm), Gudou Mountain (22.22N, 112.97E), Jiangmen City, Guangdong, coll. local, July 2018. SYSBM 001751, 1 male (35.1 × 26.0 mm), Xinhui (22.52N, 113.08E), Jiangmen City, Guangdong, coll. local, July 2018.

Colour in life.

Highly variable, even within the same population. Carapace and ambulatory legs dark brown to purple; chelipeds a combination of brown, orange and white (Fig. 2B). Blue variants are sometimes seen.

Distribution.

Guangdong: Zhuhai, Zhongshan, Jiangmen; Macau: Taipa.

Remarks.

Nanhaipotamon guangdongense has been found at only one locality in Macau (Tai Tam Hill, Taipa). One specimen (SYSBM 001646) has exopods on the G2 on both sides, the first such report for a freshwater crab (Fig. 6G). The G2 exopod is likely the result of a developmental abnormality and is an extremely rare occurrence (Gordon, 1963). The majority of brachyurans lack the male G2 exopod although it is being increasingly recognized as a normal feature among many pinnotherid crabs ( Ahyong et al. 2012; Ng and Ho 2016).

Little was previously known about N. guangdongense as it was described from a single specimen without a precise locality. Attempts to sequence the DNA of N. guangdongense were unsuccessful, probably because of formalin fixation, compounding the problem of its identification ( Shih et al. 2011). Huang et al. (2012) reported N. guangdongense from Zhuhai. Small differences in the G1 morphology, however, suggest the holotype of N. guangdongense was probably collected from another locality (Peter Ng pers. comm.). More recent collection efforts in Guangdong have found this species at multiple locations in Zhuhai, Zhongshan, and Jiangmen. Specimens from Gujing, Jiangmen (Fig. 7 A–C) most closely resemble the holotype in G1 morphology suggesting that the holotype was probably collected from that area.

Normal and blue coloured Nanhaipotamon were sympatric at a locality in Xiangzhou, Zhuhai. Nanhaipotamon zhuhaiense Huang, Huang & Ng, 2012 was described based on only three blue specimens that had a distinctive G1 that pointed laterally and not anterolaterally as seen in the normal coloured comparative specimens. More recent collections from Xiangzhou, Zhuhai, however, have found a normal coloured specimen that has a laterally pointing G1 (Fig. 7E) and also a blue specimen that has an anterolaterally pointing G1 (Fig. 7F). Therefore, the colouration of the crab does not always correspond to a particular gonopod morphology. Specimens of intermediate G1 morphology have also been collected, while one uncollected female specimen was observed to be of intermediate colour. Furthermore, the COI K2P distances between the blue specimens SYSBM 001001 (GenBank no: MK226143), SYSBM001249 (GenBank no: MK226144) and the normal coloured specimen SYSBM 001015 (GenBank no: MK226145) are 1.23% and 0.77% respectively, which is of intraspecific level among closely related congeners. This new evidence strongly suggests that the normal and blue coloured crabs are different colour phases of the same species, but the G1 morphological differences between different specimens remains to be further studied. This seems to be a similar case to that of N. hepingense Dai, 1977, and N. pinghense Dai, 1977 (see Shih et al. 2011; Huang et al. 2012). Given that we are unable to confidently separate N. zhuhaiense from N. guangdongense , we regard them as probably conspecific, but refrain from making formal taxonomic changes until further detailed comparisons can be completed.

The G1 of specimens of N. guangdongense from different localities varies (Fig. 7). It is becoming increasingly evident that intraspecific variation of gonopodal morphology in some species of Nanhaipotamon is wider than previously recognized, while external differences are often hard to detect between species, making the taxonomy of this genus problematic (Figs 5 C–E, 7; Huang et al., 2012: fig. 5; unpublished data). Clearly, there is need for a revision of this genus. To avoid compounding the problem in the future, we strongly recommend that new species of Nanhaipotamon should only be described when a large series of specimens is available to account for intraspecific variation.

Conservation status.

Nanhaipotamon guangdongense was previously assessed as Data Deficient, being known from one unspecified location in Guangdong ( Cumberlidge 2008). This species is sometimes collected for food and for the pet trade, though we are uncertain as to the extent. Nevertheless, this species has been found in many locations with a wider range than previously thought, having an extent of occurrence of around 2,400 km2 (excluding sea area) and an area of occupancy of around 1,600 km 2. As such, we suggest the conservation status of this species under IUCN criteria would be more appropriate as Least Concern (LC). Nevertheless, N. guangdongense is quite rare in Macau, being found in only one location in the Ecological Pond of Grand Taipa, and thus may warrant local conservation attention.