Nanhaipotamon macau, Huang, Chao, Wong, Kai Chin & Ahyong, Shane T., 2018

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 : 93-97

Nanhaipotamon macau sp. n. Figs 2A, 3, 4, 5, 6 A–C

Type material.

Holotype: SYSBM 001649, male (37.4 × 30.9 mm), Coloane (22.12N, 113.56E), Macau, China, forest floor, coll. K.C. Wong, July 2010. Paratypes: SYSBM 001650, female (31.3 × 25.5 mm), Coloane, Macau, China, mud burrow adjacent to small hill stream, coll. C. Huang, February 2018. SYSBM 001651, male (36.6 × 29.3 mm), same data as above. IACM, 2 males (36.5 × 31.1 mm, 34.6 × 28.5 mm), Coloane, Macau, forest floor, coll. J. Z. Huang, July 2009. AM P101301, male (27.7 × 22.9 mm), same data as above. ZRC, male (22.3 × 19.0 mm) Coloane, Macau, China, under rock in small hillstream, coll. C. Huang, January 2018.

Other material examined.

Macau: SYSBM 001652-55, 4 males (35.3 × 28.8 mm, 32.1 × 26.5 mm, 29.0 × 24.2 mm, 28.9 × 24.1 mm), Coloane, in burrows adjacent to small hill stream, coll. C. Huang, February 2018.

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 5 C–E, 6 A–C). G2 basal segment subovate (Fig. 5B).

Description.

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 3A, 4B). Front deflexed, margin ridged in dorsal view (Figs 3A, 4B). Epigastric cristae low, separated by narrow gap (Figs 3A, 4B). Postorbital cristae sharp, laterally expanded, almost fused with epibranchial teeth and epigastric cristae (Figs 3A, 4B). Branchial regions slightly swollen (Figs 3A, B, 4B). Cervical groove shallow (Figs 3A, 4B). Mesogastric region slightly convex (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). 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).

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. 5A).

Chelipeds (pereiopod I) unequal (Figs 3A, 5 F–I); less inflated in females (Figs 4B, 5H, I). Merus trigonal in cross section; margins crenulated, dorsal-outer surface granulated. Carpus with sharp spine at inner-distal angle, spinule at base (Figs 3A, 4B). Major cheliped palm length about 1.2-1.4 × height in males (n = 5), 1.3 × in female (n = 1); dactylus 0.9-1.0 × palm length in males (n = 5), 0.9 × in female (n = 1) (Fig. 5G, I). Palm surface pitted, dorsal-outer surface granulated in larger males (Fig. 5G). Dactylus as long as pollex (Fig. 5 F–I). Occlusal margin of fingers with irregular blunt teeth; slight gape when closed (Fig. 5 F–I).

Ambulatory legs (pereiopods II–V) slender, setae short, very sparse (Figs 3A, 4B). Pereiopod III merus 0.6-0.7 × carapace length in males (n = 5), 0.6 × carapace length in female (n = 1) (Figs 3A, 4B). Pereiopods V propodus 2.1-2.2 × as long as broad in males (n = 5), 2.1 × as long as broad in female (n = 1), shorter than dactylus (Figs 3A, 4B).

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. 4A). Male sterno-pleonal cavity reaching anteriorly beyond level of posterior articular condyle of cheliped coxa (Fig. 4A); deep median longitudinal groove between sternites VII, VIII (Fig. 3D). Male pleonal locking tubercle positioned at mid-length of sternite V (Fig. 3D). Female vulva ovate, medium-sized, not reaching the sutures of sternites V/VI or VI/VII, positioned closely to one another (Fig. 4D).

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. 3C). Female pleon broadly ovate (Fig. 4C).

G1 slender; in-situ, tip of terminal segment exceeding pleonal locking tubercle, almost reaching suture between thoracic sternites IV/V (Fig. 3D); subterminal segment length about 3.1 × length of terminal segment; subterminal segment tapering distally; terminal segment large, distally expanded, distal margin laminar, slightly sinuous to V-shaped, apex blunt, directed outward, orientation perpendicular to oblique to main axis of G1 (Figs 5 C–E, 6 A–C). G2 subterminal segment about 1.9 × length of flagelliform distal segment; exopod absent (Fig. 5B).

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).

Habitat.

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).

Distribution.

Coloane, Macau.

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. 5 C–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); more inflated and less rugose branchial regions (compare Figs 3A, B, 8A, B); pterygostomial region granules larger, less numerous (compare Figs 3B, 8B); the G1 tip usually points laterally and the convex anterior margin next to the tip is often lower (Figs 5 C–E, 6 A–C) (tip points anterolaterally with higher adjacent convex margin, Fig. 6D; Cheng et al. 2003: fig. 7); G1 subterminal segment length about 3.0-3.2 × length of terminal segment in N. macau sp. n. (Figs 5 C–E, 6A) (2.7 in the neotype of N. wupingense , see below, Fig. 6D). In keeping with their wide geographic separation, sequences of the COI barcoding region between N. macau sp. n. (SYSBM 001654; GenBank accession number MK226142) and N. wupingense (GenBank accession number: AB470511.1), courtesy of Hsi-Te Shih, shows a high (13.51%) Kimura 2-parameter (K2P) distance, corroborating their separate species status.

Conservation status.

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.