Tiwaripotamon keeae, Huang & Shih & Ahyong, 2024

Huang, Chao, Shih, Hsi-Te & Ahyong, Shane T., 2024, Tiwaripotamon keeae sp. nov. (Crustacea: Decapoda: Potamidae), a new miniature species of freshwater crab from the China-Vietnam border in Napo, Guangxi, Zootaxa 5476 (1), pp. 166-176 : 167-173

publication ID	https://doi.org/ 10.11646/zootaxa.5476.1.16
publication LSID	lsid:zoobank.org:pub:51009275-1E72-4E04-B112-AB436DDC81A7
DOI	https://doi.org/10.5281/zenodo.12726029
persistent identifier	https://treatment.plazi.org/id/039087AE-D828-FF93-FF61-996CFE000954
treatment provided by	Plazi
scientific name	Tiwaripotamon keeae
status	sp. nov.

Treatment

Tiwaripotamon keeae sp. nov.

[Proposed Chinese common name: ƁĦẔae]

( Figs. 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Type material. Holotype: SYSBM 002010 , male (18.0 × 13.3 mm), China-Vietnam border near Nongchang Village , Napo County, Baise City, Guangxi, China, 22.98°N, 105.84°E, on leaves of short shrubs and grasses, 1300 m a.s.l., coll. Chao Huang, August 2018 GoogleMaps . Paratypes: SYSBM 002012–002015 , 4 males (18.3 × 13.5 mm, 18.1 × 13.4 mm, 17.3 × 13.0 mm, 14.0 × 10.8 mm), same data as holotype GoogleMaps ; SYSBM 002011 , 002016–002017 , 3 females (14.8 × 11.1 mm, 20.3 × 15.0 mm, 14.9 × 11.0 mm), same data as holotype GoogleMaps ; AM P105567 , 1 male (15.1 × 11.5 mm), 1 female (18.1 × 13.5 mm), same data as holotype GoogleMaps ; ZRC 2018.1184 View Materials , 1 male (17.2 × 12.8 mm), 1 female (14.1 × 10.9 mm), same data as holotype GoogleMaps .

Diagnosis. Carapace transversely subovate, width 1.3 × length; regions at most indistinctly demarcated; dorsal surface gently convex, anterior half slightly rugose, sparsely granular; cervical groove and H-groove very shallow; external orbital margin triangular with abrupt notch between anterolateral margin;external orbital tooth small, sharp; epibranchial tooth small, blunt; anterolateral margin convex, ridged, trending upward, lined with numerous granules. Pereiopods 2–5 (first to fourth ambulatory legs) very slender; pereiopod 5 propodus length 5.2–5.7 × width in males and 5.4–5.9 × width in females; dactylus very slender, with sharp spines on margins, longer than propodus. G1 generally slender, sinuous, pointed anterolaterally, almost reaching to pleonal locking tubercle in situ; subterminal segment about 3.3 × as long as terminal segment, strongly bent outwards in situ; inner margin convex, outer margin concave in ventral view; terminal segment slender, strongly tapering, gently upturned, with small terminal aperture and small dorsal flap in ventral view.

Description. Carapace broader than long, transversely subovate, width 1.3 × length (n = 12); regions at most indistinctly demarcated; dorsal surface gently convex, anterior half slightly rugose, sparsely granular ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Frontal margin slightly ridged in dorsal view ( Fig. 1 View FIGURE 1 ). Epigastric cristae rugose, low, blunt, divided by groove ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Postorbital cristae rugose, inconspicuous ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Cervical groove and H-groove very shallow ( Fig. 1 View FIGURE 1 ). External orbital margin triangular with abrupt notch between anterolateral margin ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). External orbital tooth small, sharp ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Epibranchial tooth small, blunt ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Anterolateral margin convex, ridged, trending upward, lined with numerous granules ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Posterolateral margin straight, with low striae ( Fig. 1 View FIGURE 1 ). Epibranchial region slightly rugose, relatively flat ( Fig. 1 View FIGURE 1 ). Orbits large; supraorbital and infraorbital margins slightly ridged, lined with numerous inconspicuous granules ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ). Sub-orbital, sub-hepatic and upper parts of pterygostomial regions surface slightly rugose; divided with sutures lined with numerous inconspicuous granules; sub-branchial regions relatively flat ( Fig. 2A View FIGURE 2 ). Epistome longitudinally narrow; posterior margin of epistome evenly sinuous, median lobe rounded, confluent with lateral margins ( Fig. 2A View FIGURE 2 ).

Maxilliped 3 merus width about 1.1 × length; ischium width about 0.9 × length; merus subpolygonal with slight median depression; ischium subtrapezoidal, inner-upper margin rounded; exopod reaching to approximately onefifth of merus height, flagellum short ( Fig. 3A View FIGURE 3 ).

Chelipeds unequal in large males, subequal in females and immature specimens; surfaces generally rugose ( Fig. 4 View FIGURE 4 ). Merus cross-section trigonal, margins weakly crenulated, surfaces slightly rugose ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 , 5 View FIGURE 5 ). Carpus inner distal angle with small spine, surfaces slightly rugose ( Figs. 1 View FIGURE 1 , 5 View FIGURE 5 ). Male major cheliped palm length about 1.5–1.6 × height (n = 6), 1.5–1.7 × in females (n = 2); dactylus about 0.8–1.0 × palm length (n = 6), 1.0 × in females (n = 2) ( Figs. 4 View FIGURE 4 , 5 View FIGURE 5 ). Inner margin of fingers lined with multiple triangular, small to large teeth; with large gap when fingers closed in mature males and small gap in females and immature specimens ( Fig. 4 View FIGURE 4 ).

Pereiopods 2–5 (first to fourth ambulatory legs) very slender, surfaces generally finely rugose, with sparse setae ( Figs. 1 View FIGURE 1 , 5 View FIGURE 5 ); pereiopod 2 <pereiopod 5 <pereiopod 3 = pereiopod 4. Pereiopod 3 length 0.9–1.0 × carapace length in males (n = 7), 0.9–1.1 × in females (n = 4) ( Figs. 1 View FIGURE 1 , 5 View FIGURE 5 ). Pereiopod 5 propodus length 5.2–5.7 × width in males (n = 6) and 5.4–5.9 × width in females (n = 5); dactylus very slender, with sharp spines on margins, longer than propodus ( Figs. 1 View FIGURE 1 , 5 View FIGURE 5 ).

Male thoracic sternum pitted; sternites 1–4 wide, width about 2.0 × length ( Fig. 2B View FIGURE 2 ). Sternites 1 and 2 indistinguishably fused, forming wide triangular plate; sternites 2 and 3 fused, separated by transverse groove; sternites 3 and 4 fused, with shallow indistinct sulcus ( Fig. 2B View FIGURE 2 ). Male sternopleonal cavity relatively shallow, reaching anteriorly to level of midlength of cheliped coxae ( Fig. 2B–D View FIGURE 2 ); median longitudinal suture present between sternites 7 and 8, not reaching sternite 6 ( Fig. 2D View FIGURE 2 ). Male pleonal locking tubercle situated posterior to mid-length of sternite 5 ( Fig. 2D View FIGURE 2 ). Female vulva ovate, large, on sternite 6, posterior margin almost reaching sternite 6/7 suture ( Fig. 2F View FIGURE 2 ).

Pleon subtriangular in males ( Fig. 2C View FIGURE 2 ), semi-oval in females ( Fig. 2E View FIGURE 2 ). Male pleonites 3–6 tapering distally; pleonite 6 width about 2.5 × length; telson triangular, width about 1.6 × length ( Fig. 2B, C View FIGURE 2 ).

G1 generally slender, sinuous, pointed anterolaterally, almost reaching to pleonal locking tubercle in situ ( Fig. 2D View FIGURE 2 ). Subterminal segment about 3.3 × as long as terminal segment, strongly bent outwards in situ ( Fig. 2D View FIGURE 2 ); inner margin convex, outer margin concave in ventral view ( Fig. 3C View FIGURE 3 ). Terminal segment slender, strongly tapering, gently upturned, with small terminal aperture and small dorsal flap in ventral view ( Fig. 3C–E View FIGURE 3 ).

G2 subterminal segment with basal one-third subtriangular, abruptly tapering to slender, slightly sinuous remaining part; subterminal segment about 1.8 × length of flagelliform terminal segment ( Fig. 3B View FIGURE 3 ).

Etymology. The specific name keeae is in honor of the late Dr. Ngan Kee Ng, a carcinologist who has contributed to the research of Chinese freshwater crabs and who we will sorely miss.

Distribution. Currently only known from a single location at the China-Vietnam border near Bainan Village, Napo County, Baise City, Guangxi, China (22.98°N, 105.84°E).

Color in life. Generally dark brown to purplish with golden specks. Carapace anterolateral margins and orbital margins golden to orange coloured. Cheliped pollex and tip of dactylus orange to light orange ( Fig. 6 View FIGURE 6 ).

Habitat and ecology. Tiwaripotamon keeae was found in a montane open-canopy karst forest at around 1300 m a.s.l. At this altitude, the night-time air conditions are usually cool and humid. The first night of the survey was dry and windy and not a single specimen was observed, whereas on the next night at the same location and after some rain, many crabs were found. It seems that the crabs only emerge from hiding after dark when the humidity is very high, which is typical of other species of this genus ( Do et al. 2016). All specimens observed were perched on the leaves of small shrubs and grasses ( Fig. 6 View FIGURE 6 ). This behavior is similar to small individuals of some congeners, such as T. pluviosum and T. vixuyenense , but the larger adults of these species are mostly found on the ground ( Shih & Do 2014; Do et al. 2016; personal observation). One individual was observed feeding on a half-eaten juvenile stick insect. A single large individual of Indochinamon aff. malipoense was observed on the ground at the type locality of T. keeae . No bodies of surface water could be directly observed in this karst habitat, but we suspect that there are many depressions and crevices just below the surface that hold rainwater that the crabs use as a water source.

Remarks. Compared with congeners, sexual dimorphism in Tiwaripotamon keeae sp. nov. is slight. Males have proportionally larger and more distinctly asymmetrical chelipeds than in females, most evident in the largest males, but to a much lesser degree than in congeners, e.g., T. vixuyenense , T. vietnamicum and T. edostilus (see Shih & Do 2014: fig. 4A, fig. 6A, C, 7A, B; Ng & Ngo 2022: fig. 1A, C, 2). In T. keeae , we did not detect sexual dimorphism in the length of the ambulatory legs, being of similar proportional lengths in both sexes ( Fig. 5 View FIGURE 5 ). Females, however, tend to have proportionally more slender legs than in males as measured by the pereiopod 5 propodus proportions (see description). The G1 morphology was generally uniform between individuals. In other respects, the examined specimens agree closely.

Tiwaripotamon keeae has very slender legs, with the pereiopod 5 propodus length about 5.2–5.9 times the width, which is comparable to T. vixuyenense (about 6.5, Shih & Do 2014), T. edostilus (about 5.6, Do et al. 2016), T. xuanson (about 5.6, Do et al. 2017), T. xiurenense (about 5.3, Do et al. 2016) and T. vietnamicum (about 5.1, Shih & Do 2014), whereas other congeners have stockier legs (less than 5.0). The G1 of the new species is unremarkable and belongs to the common type also seen in T. annamense , T. xuanson , T. pingguoense , T. pluviosum , T. xiurenense and T. edostilus . However, the new species can quite easily be identified as it is the smallest within the genus, with the largest specimen observed barely over 20 mm in carapace width and fully mature (n = 12 collected specimens plus numerous individuals observed in the wild). The only species that are close to this size are T. vixuyenense and T. araneum . The largest known specimen of T. vixuyenense has a CW of 26.4 mm (n = 6, Shih & Do 2014), which is around 30% larger than that of the new species. The size of mature T. araneum , however, is currently unclear, as it is known from only a single tiny specimen (CW = 13.0 mm) that is clearly immature ( Ng & Yeo 2001; Shih & Do 2014). Apart from the small size, the proportionlly large eyes of the new species are only comparable to yet again T. vixuyenense and T. araneum , but the eyes are comparatively smaller in the former and the latter is known from only a juvenile, which typically have proportionally larger eyes than adults. All other congeners have proportionally smaller eyes. Tiwaripotamon keeae can be further separated from T. vixuyenense by its less slender legs (see above), male thoracic sternites 3 and 4 with shallow indistinct sulcus (vs. male thoracic sternites 3 and 4 not on the same level in T. vixuyenense, Shih & Do 2014 : fig. 4C), and the different G1 morphology, which is of the common type (vs. conspicuously short, stout, straight in T. vixuyenense, Shih & Do 2014 : fig. 3A). Furthermore, T. keeae differs from T. araneum in its transversely subovate carapace (vs. subquadrate in T. araneum, Ng & Yeo 2001 : fig. 3A) and more slender legs (see above).