Somanniathelphusa zanklon Ng & Dudgeon, 1992

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 : 105-107

Somanniathelphusa zanklon Ng & Dudgeon, 1992 Figs 2D, 9

Somanniathelphusa zanklon Ng & Dudgeon, 1992: figs 11-13.

Parathelphusa sinensis : Doflein 1902: 662.

Parathelphusa (Parathelphusa) sinensis : Gee 1925: 159; Wu 1934: 339.

Somanniathelphusa sinensis sinensis: Bott 1968b: 409, figs 11, 12, 30; Bott 1970a: 338;

Bott 1970b: 111, pl. 20, figs 42-44; Ng, 1988: 105.

Somanniathelphusa sinensis : Dai 1999: 67, fig. 29, pl. 2.

Material examined.

SYSBM 101001, 1 male (27.2 × 23.1 mm), Nanping (22.19N, 113.5E), Zhuhai City, Guangdong, reservoir, coll. C. Huang, April 2015. SYSBM 101002-101003, 2 males (38.8 × 31.9 mm, 30.4 × 25.6 mm), Jinding (22.38N, 113.54E), Zhuhai City, Guangdong, coll. local, May 2014. SYSBM 101004-101005, 2 males (42.0 × 33.5 mm, 34.2 × 28.1 mm), Sun Yat-sen University (23.10N, 113.30E), Guangzhou City, Guangdong, fish pond, coll. C. Huang, June 2013. SYSBM 101006, 1 female (37.1 × 29.5 mm), same data as above. SYSBM 101007, 1 male (30.6 × 24.5 mm), Coloane (22.12N, 113.56E), Macau, reservoir, coll. K.C. Wong, July 2008. SYSBM 101008, 1 male (28.2 × 22.5 mm), Coloane, Macau, reservoir, coll. K.C. Wong, July 2009. IACM, 1 male (24.2 × 19.8 mm), Coloane, Macau, reservoir, coll. K.C. Wong, February 2013. SYSBM 101009-101010, 2 males (19.5 × 16.8 mm, 19.2 × 16.4 mm), Shenzhen City (22.6N, 114.0E), Guangdong, coll. local, August 2015. SYSBM 101011, 1 female (19.6 × 16.4 mm), same data as above. SYSBM 101015-101016, 2 males (35.7 × 28.4 mm, 37.2 × 29.9 mm), Sihui City (23.12N, 113.56E), Guangdong, coll. local, August 2013. SYSBM 101017, 1 female (31.6 × 25.9 mm), same data as above. SYSBM 101018-101020, 3 males (38.2 × 30.8 mm, 35.4 × 28.1 mm, 28.3 × 21.3 mm), Renhua, Shaoguan City, Guangdong, coll. local, August 2013. SYSBM 101021, 1 male (31.5 × 26.6 mm), Lianhua Mountain, Shanwei City, Guangdong, coll. local, October 2013. SYSBM 101022, 1 female (27.3 × 23.2 mm), same data as above. SYSBM 101030, 1 male (39.4 × 33.0 mm), Heyuan City, Guangdong, coll. Z.C. Zhou, January 2014. SYSBM 101031, 1 female (32.4 × 27.3 mm), same data as above. SYSBM 101032-101035, 4 males (35.0 × 28.3 mm, 32.7 × 26.9 mm, 30.8 × 25.0 mm, 25.9 × 21.7 mm), Raoping, Chaozhou City, Guangdong, coll. Z.C. Zhou, January 2014. SYSBM 101036, 1 female (24.6 × 20.8 mm), same data as above. SYSBM 101037-101040, 4 males (26.3 × 20.4 mm, 30.9 × 25.8 mm, 26.6 × 23.0 mm, 27.0 × 22.5 mm), Wenzhou City, Zhejiang, coll. local, October 2013. SYSBM 101041, 1 female (29.8 × 24.6 mm), same data as above.

Colour in life.

Generally brown overall; larger individuals may have dark markings near the cardiac region (Fig. 2D).

Distribution.

Coloane, Macau; Guangdong: Guangzhou City, Shenzhen City, Zhuhai City, Sihui City, Shaoguan City, Shanwei City, Heyuan City, Chaozhou City; Zhejiang: Wenzhou City.

Remarks.

Ng and Dudgeon (1992) showed former records of Somanniathelphusa sinensis (H. Milne Edwards, 1853) from southern China (Bott 1968, 1970; Dai 1999) to represent a new species, S. zanklon. Shih et al. (2007) included S. zanklon from Hong Kong and Guangdong (Dongguan City and Nanhai City) and showed that specimens of Somanniathelphusa from eastern Guangdong, Fujian and west-central Taiwan were all very closely related genetically, probably even conspecific. Specimens examined here from different localities were all very similar morphologically (Fig. 9), with those from Zhejiang Province having a slightly longer G1 distal part (Fig. 9H), though the overall shape is very much like the others. We tentatively treat all of these as the same species pending a full revision. Interestingly, Dai (1999) also reported the genus from Zhejiang, but none of the species of Somanniathelphusa in her monograph lists Zhejiang among its localities. The Chinese Somanniathelphusa are particularly problematic as many species look identical externally and were described based on minute differences that we find difficult to detect. Furthermore, being lowland species, they are readily dispersed by floods and are commonly found in aquaculture ponds where their newly hatched crablings are easily translocated. Preliminary genetic evidence suggests that the species diversity of Somanniathelphusa may have been overestimated ( Shih et al. 2007).

Conservation status.

Somanniathelphusa zanklon is currently assessed as Endangered ( Esser and Cumberlidge 2008) as it was known from fewer than five locations in Hong Kong with a extant of occurrence less than 5,000 km2, with degrading habitat quality. Our study, however, finds this species to have a widespread occurrence in south-east China with an area of occupancy estimated at over 120,000 km2. Though habitat quality in some of these locations is declining, this resilient lowland species seems to be able to thrive in most water bodies that are not heavily polluted. As such, we find that S. zanklon does not satisfy any IUCN Red List threat categories and thus we suggest Least Concern would be a more appropriate determination at present. In Macau, all known occurrences of S. zanklon are from Hac-Sa Reservoir, Coloane, although it most likely also occurs in other water bodies in Coloane. There was an unconfirmed sighting of S. zanklon in Taipa a few years ago by the second author, though more recent surveys have failed to locate any specimens. There are three large water bodies on the Macau peninsula, of which only one reservoir on the east, next to Parque Municipal do Monte da Guia, which sources freshwater from the mainland, is suitable for lowland freshwater crabs. Although we did not survey this reservoir, it very likely also holds S. zanklon as this species was found in one of its water source reservoirs in Zhuhai. The other two water bodies, Sai Van Lake and Nam Van Lake, were once bays that have mostly been artificially closed off by landfill and currently hold sea water.