Nanhaipotamon aureomarginatum, Huang & Mao & Shih, 2021

Huang, Chao, Mao, Siying & Shih, Hsi-Te, 2021, Two new freshwater crab species of the genus Nanhaipotamon Bott, 1968 (Crustacea, Decapoda, Potamidae) from Huizhou, Guangdong Province, southern China, Zootaxa 5026 (2), pp. 221-238 : 228-232

publication ID	https://doi.org/ 10.11646/zootaxa.5026.2.4
publication LSID	lsid:zoobank.org:pub:F69E5D4A-925D-46B3-BBA7-4712FF2E206B
DOI	https://doi.org/10.5281/zenodo.5275084
persistent identifier	https://treatment.plazi.org/id/441A93FB-91A0-4FF3-9945-2EE9885B81BB
taxon LSID	lsid:zoobank.org:act:441A93FB-91A0-4FF3-9945-2EE9885B81BB
treatment provided by	Plazi
scientific name	Nanhaipotamon aureomarginatum
status	sp. nov.

Treatment

Nanhaipotamon aureomarginatum View in CoL n. sp.

( Figs. 4–6 View FIGURE 4 View FIGURE 5 View FIGURE 6 , 7K, L View FIGURE 7 , 8C View FIGURE 8 )

urn:lsid:zoobank.org:act:441A93FB-91A0-4FF3-9945-2EE9885B81BB

Type material. Holotype: SYSBM 001807 , male (37.7 × 30.7 mm), Huidong County [ca. 23.0°N, 114.7°E], Huizhou City , Guangdong Province, China, burrow in soft mud near hillstream, 100 m a.s.l., coll. C. Huang, November 2018. GoogleMaps

Paratypes: SYSBM 001809–001812 , 4 males (30.9 × 25.3 mm, 29.1 × 23.2 mm, 27.4 × 22.3 mm, 24.7 × 20.5 mm), same data as holotype GoogleMaps ; SYSBM 001808 , 001813–001815 , 4 females (33.9 × 28.4 mm, 29.6 × 24.9 mm, 19.24 × 16.1 mm, 13.5 × 11.1 mm), same data as holotype GoogleMaps ; NCHUZOOL 17035, male (26.5 × 21.5 mm), same data as holotype GoogleMaps ; NCHUZOOL 17036, female (25.5 × 20.8 mm), same data as holotype GoogleMaps ; AM P.105615, male (28.9 × 23.2 mm), same data as holotype GoogleMaps ; AM P.105615, female (17.9 × 15.0 mm), same data as holotype GoogleMaps .

Diagnosis. Carapace broader than long, regions indistinct ( Fig. 4 View FIGURE 4 ). Dorsal surface generally smooth, pitted, convex, slightly rugose on anterolateral regions in smaller specimens ( Fig. 4 View FIGURE 4 ). Anterolateral margins cristate with fused granules, bent inward posteriorly ( Fig.4 View FIGURE 4 ). Posterolateral surfaces with low,oblique striae converging posteriorly; granules scattered among striae, some merged together ( Fig. 4 View FIGURE 4 ). Sub-orbital, pterygostomial regions covered with large round granules; sub-hepatic region with lines of fused smaller granules ( Fig. 5A View FIGURE 5 ). Maxilliped III exopod reaching to proximal one-third of merus, with flagellum ( Fig. 6A View FIGURE 6 ). G1 slender, reaching beyond suture between sternites IV/V in situ ( Fig. 5D View FIGURE 5 ). G1 subterminal segment 2.1–2.2 × as long as terminal segment. G1 terminal segment large, duck head-shaped; mesial margin strongly convex; outer margin strongly concave; anterior margin almost straight, oblique to longitudinal axis of G1; apex pointing outwards ( Figs. 6C–E View FIGURE 6 , 7K, L View FIGURE 7 ). G2 subterminal segment 1.7–1.8 × as long as flagellum-like terminal segment ( Fig. 6B View FIGURE 6 ).

Description. Carapace broader than long, width 1.2–1.3 × length (n = 13), regions indistinct ( Fig. 1 View FIGURE 1 ). Dorsal surface generally smooth, pitted, convex, slightly rugose on anterolateral regions in smaller specimens ( Fig. 4 View FIGURE 4 ). Front deflexed, margin slightly ridged in dorsal view ( Fig. 4 View FIGURE 4 ). Epigastric cristae low, separated by a narrow gap ( Fig. 4 View FIGURE 4 ). Postorbital cristae prominent, laterally extended, almost fused with epigastric cristae and epibranchial teeth ( Fig. 4 View FIGURE 4 ). Branchial regions inflated; cervical grooves shallow; mesogastric region convex ( Fig. 4 View FIGURE 4 ). External orbital teeth blunt, triangular with gently convex outer margins, each separated from anterolateral margin by small gap ( Figs. 4 View FIGURE 4 , 5A View FIGURE 5 ). Epibranchial teeth small, granular ( Figs. 4 View FIGURE 4 , 5A View FIGURE 5 ). Anterolateral margins cristate with fused granules, bent inward posteriorly ( Fig. 4 View FIGURE 4 ). Posterolateral surfaces with low, oblique striae converging posteriorly; granules scattered among striae, some merged together ( Fig. 4 View FIGURE 4 ). Orbits large; supraorbital and infraorbital margins cristate ( Figs. 4 View FIGURE 4 , 5A View FIGURE 5 ). Sub-orbital, pterygostomial regions covered with large round granules; sub-hepatic region with lines of fused smaller granules ( Fig. 5A View FIGURE 5 ). Epistome median lobe broadly triangular, lateral margins sinuous ( Fig. 5A View FIGURE 5 ).

Maxilliped III with merus subtrapezoidal, about as wide as long, median depression distinct; ischium; ischium subtrapezoidal, width about 0.7 × length with distinct median sulcus, with anterior mesial margin rounded; exopod reaching to proximal one-third of merus, with flagellum ( Fig. 6A View FIGURE 6 ).

Chelipeds (pereiopod I) unequal, relatively less inflated in females ( Figs. 4 View FIGURE 4 , 6F–I View FIGURE 6 ). Merus trigonal in cross section, margins lined with granules, outer-dorsal surface rugose ( Figs. 4 View FIGURE 4 , 5A View FIGURE 5 ). Carpus with long, acute spine at inner-distal angle, spinule at base, dorsal surface rugose ( Fig. 4 View FIGURE 4 ). Major cheliped palm length about 1.3–1.4 × height in males (n = 6), 1.4 × in females (n = 3); dactylus about 1.0–1.1 × palm length in both males (n = 6) and females (n = 3) ( Fig. 6F–I View FIGURE 6 ). Palm surface pitted, dorsal surface rugose. Dactylus as long as pollex. Occlusal margin of fingers lined with irregular blunt teeth, slight gape when finger tips in contact ( Fig. 6F–I View FIGURE 6 ).

Ambulatory legs (pereiopods II–V) slender, with short and sparse setae. Pereiopods III merus 0.7 × carapace length in males (n = 6), 0.6–0.7 × in females (n = 3). Pereiopods V propodus 2.0–2.4 × as long as broad in males (n = 6), 2.2–2.3 × in females (n = 3) ( Fig. 4 View FIGURE 4 ).

Male thoracic sternum generally smooth, pitted; sternites I–IV relatively narrow, width 1.4 × as length ( Fig. 5B, C View FIGURE 5 ). Sternites I, II fused, appearing broadly triangular; sternites II, III separated by shallow transverse sulcus, reaching edge of sternum; sternites III, IV fused, with barely visible demarcation ( Fig. 5B, C View FIGURE 5 ). Male sterno-pleonal cavity reaching anteriorly to level of mid-length of cheliped coxa ( Fig. 5B–D View FIGURE 5 ); median longitudinal groove separating sternites VII, VIII deep ( Fig. 5D View FIGURE 5 ). Male pleonal locking tubercles positioned at mid-length of sternites V ( Fig. 5D View FIGURE 5 ). Adult female vulvae ovate, relatively large but not reaching sternites V or VII; positioned closely to one another, orientation oblique to longitudinal axis of sterno-pleonal cavity ( Fig. 5F View FIGURE 5 ).

Pleon and telson triangular in males ( Fig. 5C View FIGURE 5 ) and broadly ovate in females ( Fig. 5E View FIGURE 5 ). Male pleonites III–VI progressively narrower, lateral margins nearly straight; pleonite VI 1.9 × as broad as long. Male telson 1.2 × as broad as long, with blunt apex ( Fig. 5C View FIGURE 5 ).

G1 slender, reaching beyond suture between sternites IV/V in situ ( Fig. 5D View FIGURE 5 ). G1 subterminal segment 2.1–2.2 × as long as terminal segment (n = 3). G1 terminal segment large, duck head-shaped; mesial margin strongly convex; outer margin strongly concave; anterior margin almost straight, oblique to longitudinal axis of G1; apex pointing outwards ( Figs. 6C–E View FIGURE 6 , 7K, L View FIGURE 7 ). G2 subterminal segment 1.7–1.8 × as long as flagellum-like terminal segment (n = 3) ( Fig. 6B View FIGURE 6 ).

Etymology. The specific name “ aureomarginatum ” alludes to the new species’ golden-coloured anterolateral margins of the carapace. The name thus is to be conceived as an adjective in the nominative singular.

Colour in life. Colour variable. Carapace generally brown to dark purple; anterolateral margins, orbital margins, and granules and striae on frontal and lateral regions of carapace golden to bright orange. Ambulatory legs olive yellow to dark purple. Chelipeds light bluish grey to orange. Juveniles usually completely brown.

Habitat. Nanhaipotamon aureomarginatum n. sp. is a lowland semi-terrestrial species found at around 100 m a.s.l. While it is sympatric with Nanhaipotamon aff. hongkongense at the type locality, the two species seem to be ecologically distinct. The smaller sized N. aff. hongkongense digs in the gravelly soil at the water’s edge next to the larger and fast flowing streams, whereas N. aureomarginatum n. sp. is more terrestrial and prefers to burrow in soft mud near the smaller branches of the hillstream or seeps.

Remarks. The overall intraspecific morphological variation is low. The general shape of the G 1 in N. aureomarginatum n. sp. seems to be quite stable ( Fig. 6C–E View FIGURE 6 ). While externally a typical Nanhaipotamon , the proportionately large G1 terminal segment of N. aureomarginatum n. sp. ( Figs. 6C–E View FIGURE 6 , 7K, L View FIGURE 7 ) is unique amongst all congeners, with only the exceptions of N. macau and N. wupingense ( Figs. 3C–E View FIGURE 3 , 7I, J View FIGURE 7 ; Huang et al. 2018 b). Nanhaipotamon aureomarginatum n. sp. can be nevertheless differentiated from the latter two species by the higher and rounded inner distal margin of the G1 terminal segment ( Fig. 6C–E View FIGURE 6 , 7K, L View FIGURE 7 ) [vs. G1 terminal segment with inner distal margin lower and sinuous in N. macau ( Huang et al. 2018 b: fig. 6C) and N. wupingense ( Huang et al. 2018 b: fig. 6D)]. In the field, the new species can easily be separated with the sympatric N. aff. hongkongense by the live colouration (see “colour in life”; Fig. 8C View FIGURE 8 ) (vs. dark red to red in N. aff. hongkongense ; Fig. 8D View FIGURE 8 ).

Conservation status. Nanhaipotamon aureomarginatum n. sp. is likely highly endemic. Its bright colours make it a prime target for collection for the pet trade. With this consideration, we choose to remain discreet about the exact locality of the new species.