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)

Abstract Four species of freshwater crabs from three genera and two families (Cantopotamonhengqinense Huang, Ahyong & Shih, 2017, Nanhaipotamonguangdongense Dai, 1997, Nanhaipotamonmacausp. n., and Somanniathelphusazanklon Ng & Dudgeon, 1992) are documented from Macau for the first time. One new species, Nanhaipotamonmacausp. n., is described. The large flap on the male first gonopod terminal segment sets it apart from all other known congeners except N.wupingense Cheng, Yang, Zhong & Li, 2003, from Fujian. Characters of the carapace, male first gonopod and size, however, clearly differentiate these two species. Preliminary genetic studies also suggest that the two are not closely related. A neotype is designated for N.wupingense. The taxonomic status of Nanhaipotamonguangdongense is also discussed. Notes on the general biology and conservation status of these crabs are also included.

Distribution. Hengqin Island, Zhuhai, Guangdong; Coloane, Macau. Conservation status. Cantopotamon hengqinense was previously only known from three hill streams in Dahengqin Mountain in Hengqin Island. This study found it to be present in another three hill streams in the neighbouring southwest corner of Coloane, Macau, which extends its extent of occurrence to 34.6 km 2 (excluding sea area), area of occupancy to 11.7 km 2 and number of locations to two. The populations in Hengqin and Macau are currently isolated from each other by a narrow strip of sea. Unlike the Hengqin population, whose habitat is threatened by urban development (Huang et al. 2017), the Macau population does not face serious imminent threat as all localities at which it was found are not currently open to development. Specimens from Macau are morphologically indistinguishable from those found in Hengqin Island. Cantopotamon hengqinense has not been found in Xiangzhou, Zhuhai to the north and Sanzao Island to the west despite considerable survey efforts during 2011-2018. In fact, no species of Cantopotamon are known from Sanzao Island, where instead Cryptopotamon anacoluthon (Kemp, 1918) is abundant. Given that the extent of occurrence and area  Dai, 1997, male (35.9 × 28.8 mm), SYSBM 001645 (B); Cantopotamon hengqinense Huang, Ahyong & Shih, 2017, male, specimen not collected (C); Somanniathelphusa zanklon Ng & Dudgeon, 1992, photographed in Zhuhai, specimen not collected (D). of occupancy of C. hengqinense is much lower than 5, 000 km 2 and 5000 km 2 , respectively, with fewer than five known locations and projected decline in habitat quality in Hengqin, the suggested corresponding conservation status of this species under IUCN Red List criteria remains as indicated by Huang et al. (2017), as Endangered B2(a)(b). Diagnosis. Carapace broader than long, regions indistinct, dorsal surface convex, anterolateral region weakly rugose (Figs 3A, 4B); postorbital cristae sharp, laterally expanded, almost fused with epibranchial teeth and epigastric cristae (Figs 3A, 4B); external orbital angle sharply triangular, outer margin gently convex to almost straight, separated from anterolateral margin by conspicuous gap (Figs 3A, B, 4B); sub-orbital regions covered by sparse low granules, pterygostomial regions covered with short rows of a few rounded granules; sub-hepatic regions covered with lined striae (Fig. 3B); maxilliped III exopod reaching to proximal one-third of merus with short flagellum (Fig. 5A); female vulva ovate, medium-sized, positioned closely to one another (Fig. 4D); male pleon triangular, lateral margins almost straight (Fig. 3C); G1 slender, subterminal segment tapering distally, terminal segment large, distally expanded, distal margin laminar, apex blunt, directed outward (Figs 5C-E, 6A-C). G2 basal segment subovate (Fig. 5B  angle sharply triangular, outer margin gently convex to almost straight, separated from anterolateral margin by conspicuous gap (Figs 3A,B,4B). Epibranchial tooth small, granular, indistinct (Figs 3A, B, 4B). Anterolateral margin cristate, lined with 20-23 granules, less distinct in some larger specimens; bent inward posteriorly (Figs 3A, 4B). Posterolateral surface with low, oblique striae, converging towards posterior carapace margin (Figs 3A, 4B). Orbits large; supraorbital, infraorbital margins cristate (Fig. 3B). Sub-orbital regions covered by sparse low granules, pterygostomial regions covered with short rows of a few rounded granules; sub-hepatic regions covered with lined striae (Fig. 3B). Epistome posterior margin narrow; median lobe broadly triangular, lateral margins slightly sinuous (Fig. 3B).
Etymology. This species is named after the type locality, Macau; used as a noun in apposition.
Colour in life. Variable, carapace and ambulatory legs dark brown to purple; chelipeds a combination of brown, orange and white ( Fig. 2A).

Remarks.
As with many other species of Nanhaipotamon, N. macau sp. n. shows intraspecific variation in G1 morphology. In the terminal segment, the curves of the inner-distal and distal margins vary ( Fig. 5C-E). The general shape and large size of the terminal segment, however, readily separates N. macau from other congeners in the Pearl River Delta Region, such as N. guangdongense Dai, 1997 (Fig. 7).
Nanhaipotamon wupingense Cheng, Yang, Zhong & Li, 2003, from Fujian Province, is the only other known congener that also possesses such a large terminal segment. Based on the redscription of N. wupingense below, N. macau sp. n. differs by its larger maximum size (CW to 37.4 mm vs 27.5 mm in N. wupingense; Cheng et al. 2003 Conservation status. Nanhaipotamon macau sp. n. has an extremely restricted distribution with an extent of occurrence of only 5.3 km 2 (excluding sea area) and an area of occupancy of around 3 km 2 . However, all 12 hill streams at which N. macau sp. n. was found are not currently open to urban development (one of these, Ka-Ho Reservoir Freshwater Wetland, is a protected area) and they seem to be locally abundant. We are unaware of any commercial harvesting of these crabs for human consumption or the aquarium trade. As such, no imminent threats to this species are apparent and it cannot be assigned to any level of threat according the IUCN Red List criteria. However, we emphasize the fragility of this species due to its highly restricted distribution; the habitat integrity of the hills of Coloane is paramount to this species' survival. Dai, 1997 Figs 2B, 6G, 7 Nanhaipotamon guangdongense Dai, 1997: 229, fig. 9;Dai 1999: 121, pl   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.

Nanhaipotamon guangdongense
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. 7A-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. 2011Huang 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 5C-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 km 2 (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.  13.0 × 10.5 mm, 25.3 × 20.8 mm, 23.4 × 19.5 mm, 24.9 × 20.3 mm, 21.6 × 17.6 mm, 16.9 × 13.7 mm, 14.8 × 11.7 mm, 15.2 × 12.4 mm), same data as neotype.
Remarks. The original description of Nanhaipotamon wupingense is brief and minimally illustrated (Cheng et al. 2003), neither describing nor figuring details of the carapace physiognomy and pterygostomial ornamentation, which are diagnostic differences between N. wupingense and N. macau sp. n. Although the gonopods of N. wupingense were described and figured, and were distinctive at the time of original description, they are similar to that to the newly discovered N. macau sp. n. As such the type account of N. wupingense could apply equally to N. macau sp. n. Unfortunately, the type material of N. wupingense is now lost: according to the first author of N. wupingense, the type material of N. wupingense, which was originally deposited in Fujian Research Institute of Parasite Disease, Fuzhou, Fujian Province, was lost during relocation (YZ Cheng, pers. comm.). Therefore, in order to fix the identity of N. wupingense and allow adequate characterization of both species, we hereby designate a neotype for N. wupingense in accordance to ICZN (1999: art. 75.3). The neotype of N. wupingense (male,22.4 × 18.3 mm,JX 050563) and other examined specimens of the species were collected from the original type locality. The neotype G1 corresponds well to that originally described and figured for N. wupingense, although we note some minor differences in morphometrics compared to the original type description (Cheng et al. 2003). The G1 subterminal/terminal segment length ratio of N. wupingense is 3.0 according to Cheng et al. (2003), but, we measure the ratio at 2.7 in the neotype (Fig. 6D) and 2.6 based on the illustration of the G1 of the holotype (Cheng et al. 2003: fig. 7). The G2 subterminal/terminal segment length ratio of N. wupingense is inconsistently recorded in Cheng et al. (2003): 1.8 in the Chinese description, erroneously as 2.7 in the English abstract, and 2.0 if based on the figure of the holotype G2 (Cheng et. al. 2003: fig. 6). This ratio could not be measured for the neotype as the G2 terminal segment broke off inside the G1 during dissection, although the ratio in JX 050564, a sub-adult, is 2.2 (Fig. 6F). The G1 is not fully developed in this specimen (Fig. 6E).

Family Gecarcinucidae Rathbun, 1904 Genus Somanniathelphusa Bott, 1968
Somanniathelphusa zanklon Ng & Dudgeon, 1992Figs 2D, 9 Somanniathelphusa zanklon Ng & Dudgeon, 1992: figs 11-13. Parathelphusa sinensis: Doflein 1902: 662. Parathelphusa (Parathelphusa) sinensis: Gee 1925Wu 1934: 339. Somanniathelphusa sinensis sinensis: Bott 1968bBott 1970a: 338;Bott 1970b: 111, pl. 20, figs 42-44;Ng, 1988: 105. Somanniathelphusa sinensis: Dai 1999 fig. 29 Colour in life. Generally brown overall; larger individuals may have dark markings near the cardiac region (Fig. 2D). Remarks. Ng and Dudgeon (1992) showed former records of Somanniathelphusa sinensis (H. Milne Edwards, 1853) from southern China (Bott 1968(Bott , 1970Dai 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 km 2 , 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 km 2 . 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.