Research Article |
Corresponding author: Shane T. Ahyong ( shane.ahyong@austmus.gov.au ) Academic editor: Sammy De Grave
© 2018 Chao Huang, Kai Chin Wong, Shane T. Ahyong.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Huang C, Wong KC, Ahyong ST (2018) The freshwater crabs of Macau, with the description of a new species of Nanhaipotamon Bott, 1968 and the redescription of Nanhaipotamon wupingense Cheng, Yang, Zhong & Li, 2003 (Crustacea, Decapoda, Potamidae). ZooKeys 810: 91-111. https://doi.org/10.3897/zookeys.810.30726
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Four species of freshwater crabs from three genera and two families (Cantopotamon hengqinense Huang, Ahyong & Shih, 2017, Nanhaipotamon guangdongense Dai, 1997, Nanhaipotamon macau sp. n., and Somanniathelphusa zanklon Ng & Dudgeon, 1992) are documented from Macau for the first time. One new species, Nanhaipotamon macau sp. 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 Nanhaipotamon guangdongense is also discussed. Notes on the general biology and conservation status of these crabs are also included.
Freshwater crabs, Gecarcinucidae , Macau, new species, Potamidae , systematics
Best known as the gambling capital of the world, Macau (also known as Macao) has a total land area of only 30.8 km2 but a population of more than 650,000 people, making it one of the most densely populated regions in the world (Government of Macao Special Administrative Region Statistics and Census Service). Macau historically consists of the Macau Peninsula (bordered by Zhuhai to the north) and two islands: Taipa and Coloane. The two islands are now joined by Cotai, an area created by land reclamation in 2005.
The freshwater crabs of Macau have not been scientifically documented to the best of our knowledge. General wetland faunal surveys from 2007 onwards have found freshwater crabs in Coloane resulting in a small collection kept in the Macao Civic and Municipal Affairs Bureau. Upon examination, it was found that these freshwater crab specimens contained three species, Cantopotamon hengqinense Huang, Ahyong & Shih, 2017, Somanniathelphusa zanklon Ng & Dudgeon, 1992, and a new species of Nanhaipotamon Bott, 1968. This has led to more extensive surveys in 2018, covering 14 survey points (two in Taipa and 12 in Coloane; Fig.
Specimens were collected by hand and preserved in 75% ethanol from 2007 onwards from South China. They are deposited in the Sun Yat-sen Museum of Biology, Sun Yat-sen University, Guangzhou, China (
G1 male first gonopod;
G2 male second gonopod;
CW carapace width.
The terminology used primarily follows that of
Cantopotamon hengqinense Huang, Ahyong & Shih, 2017: 9, fig. 5.
Holotype:
The freshwater crabs of Macau, colour in life. Nanhaipotamon macau sp. n., male (29.0 × 24.2 mm),
China: IACM, 2 males (20.5 × 16.5 mm, 19.5 × 16.5 mm), Coloane (22.12N, 113.56E), Macau, small hillstream, under rocks, coll. K.C. Wong, November 2009.
Hengqin Island, Zhuhai, Guangdong; Coloane, Macau.
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 km2 (excluding sea area), area of occupancy to 11.7 km2 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 (
Holotype:
Macau:
Carapace broader than long, regions indistinct, dorsal surface convex, anterolateral region weakly rugose (Figs
Nanhaipotamon macau sp. n., male holotype (37.4 × 30.9 mm),
Nanhaipotamon macau sp. n., male holotype (37.4 × 30.9 mm),
Carapace broader than long, width about 1.2 × length (n = 6); regions indistinct, dorsal surface convex; surface generally smooth, pitted, anterolateral region weakly rugose (Figs
Maxilliped III merus about as wide as long; ischium width about 0.7 × length; merus subtrapezoidal, with median depression; ischium subtrapezoidal, with distinct median sulcus, mesial margin rounded. Exopod reaching to proximal one-third of merus; flagellum short (Fig.
Chelipeds (pereiopod I) unequal (Figs
Ambulatory legs (pereiopods II–V) slender, setae short, very sparse (Figs
Male thoracic sternum generally smooth; sternites I–IV narrow, width about 1.5 × length; sternites I, II forming triangular structure; sternites II, III fused, but demarcated by shallow transverse sulcus; sternites III, IV fused, demarcation inconspicuous (Fig.
Male pleon triangular; somites III–VI progressively narrower, lateral margins almost straight; somite VI width 1.8–2.1 × length (n = 6); telson width 1.3–1.4 × length (n = 6); apex rounded (Fig.
G1 slender; in-situ, tip of terminal segment exceeding pleonal locking tubercle, almost reaching suture between thoracic sternites IV/V (Fig.
This species is named after the type locality, Macau; used as a noun in apposition.
Variable, carapace and ambulatory legs dark brown to purple; chelipeds a combination of brown, orange and white (Fig.
Nanhaipotamon macau sp. n. is a typical semi-terrestrial species that burrows in wet soil in the bank adjacent to hill streams. It was sympatric with Cantopotamon hengqinense at three localities (22.117N, 113.566E; 22.118N, 113.559E; 22.128N, 113.561E).
Coloane, Macau.
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.
Comparison of G1 of Nanhaipotamon guangdongense Dai, 1997, from different localities. Male (38.4 × 31.5 mm),
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;
Nanhaipotamon macau sp. n. has an extremely restricted distribution with an extent of occurrence of only 5.3 km2 (excluding sea area) and an area of occupancy of around 3 km2. 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.
Nanhaipotamon
guangdongense
Dai, 1997: 229, fig. 9;
Holotype: AS-CB 05141, male (33.2 × 26.4 mm), Guangdong Province, China, gift from Sun Yat-Sen Medical College, no date [photographs 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.
Highly variable, even within the same population. Carapace and ambulatory legs dark brown to purple; chelipeds a combination of brown, orange and white (Fig.
Guangdong: Zhuhai, Zhongshan, Jiangmen; Macau: Taipa.
Nanhaipotamon guangdongense has been found at only one locality in Macau (Tai Tam Hill, Taipa). One specimen (
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 (
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.
The G1 of specimens of N. guangdongense from different localities varies (Fig.
Nanhaipotamon guangdongense was previously assessed as Data Deficient, being known from one unspecified location in Guangdong (
Nanhaipotamon wupingense Cheng, Yang, Zhong & Li, 2003: 678, figs 1–8.
Neotype: JX 050563, male (22.4 × 18.3 mm), Xiaba (24.89N, 116.05E), Wuping county, Longyan City, Fujian Province, China, coll. X. M. Zhou, May 2007.
JX 050564, JX 050566, JX 050568–050569, 4 males (16.2 × 13.2 mm, 15.5 × 12.6 mm, 13.0 × 10.9 mm, 14.0 × 11.5 mm), same data as neotype. JX 050565, JX 050567, JX 050570–050576, 9 females (16.1 × 13.2 mm, 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.
Carapace broader than long, width about 1.2 × length (n = 14); regions indistinct, dorsal surface convex; surface generally smooth, pitted, anterolateral region slightly rugose (Fig.
Nanhaipotamon wupingense Cheng, Yang, Zhong & Li, 2003, male neotype (22.4 × 18.3 mm), JX 050563 (A–D); female (25.3 × 20.8 mm), JX 050570 (E–F). Dorsal habitus (A); cephalothorax, anterior view (B); anterior thoracic sternum and pleon, ventral view (C); sterno-pleonal cavity with right G1in situ (left G1 removed), ventral view (D); pleon, ventral view (E); vulvae, ventral view (F).
Maxilliped III merus about as wide as long; ischium width about 0.7 × length; merus subtrapezoidal, with median depression; ischium subtrapezoidal, with distinct median sulcus, mesial margin rounded. Exopod reaching to proximal one-third of merus; flagellum short.
Chelipeds (pereiopod I) unequal (Fig.
Ambulatory legs (pereiopods II–V) slender, setae short, very sparse (Fig.
Male thoracic sternum generally smooth; anterior thoracic sternum (sternites I–IV) narrow, width about 1.5 × length; sternites I, II forming triangular structure; demarcation between sternites II, III complete; sternites III, IV fused with vestigial median suture (Fig.
Male pleon triangular, lateral margins almost straight; somites III–VI progressively narrower; somite VI width 2.1–2.2 × length (n=2); telson width 1.2–1.3 × length (n=2); apex rounded (Fig.
G1 slender; in-situ, tip of terminal segment exceeding pleonal locking tubercle, reaching suture between thoracic sternites IV/V (Fig.
Currently only known from Xiaba, Wuping County, Longyan City, Fujian.
The original description of Nanhaipotamon wupingense is brief and minimally illustrated (
Somanniathelphusa zanklon Ng & Dudgeon, 1992: figs 11–13.
Parathelphusa
sinensis
:
Parathelphusa (Parathelphusa) sinensis
:
Somanniathelphusa
sinensis
sinensis
:
Somanniathelphusa
sinensis
:
Generally brown overall; larger individuals may have dark markings near the cardiac region (Fig.
Coloane, Macau; Guangdong: Guangzhou City, Shenzhen City, Zhuhai City, Sihui City, Shaoguan City, Shanwei City, Heyuan City, Chaozhou City; Zhejiang: Wenzhou City.
Comparison of G1 of Somanniathelphusa zanklon Ng & Dudgeon, 1992, from different localities. Male (30.6 × 24.5 mm),
Somanniathelphusa zanklon is currently assessed as Endangered (
This project was partly funded by the PANGEA research centre student grants program (UNSW) to the first author. Special thanks are expressed to XM Zhou, JX Zou, and their students (Nanchang University) for assisting the first author in examining specimens at Nanchang University, and to ZC Zhou for his donations of several Somanniathelphusa specimens. We would also like to acknowledge H-T Shih for providing genetic sequences for use in this study, and to Tohru Naruse, Savel R. Daniels and the editors for greatly improving the manuscript.