On a new species of freshwater crab, Indochinamonkhinpyae, from northern Myanmar (Crustacea, Brachyura, Potamidae)

Abstract A new species of freshwater crab of the genus Indochinamon Yeo & Ng, 2007 (family Potamidae), is described from highlands north of Myitkyina in Kachin State, Myanmar. Indochinamonkhinpyaesp. n. is distinguished from congeners by its very rugose carapace, broad male pleon and distinctively structured male first gonopod; and is the first potamid species recorded from northern Myanmar.

Third maxillipeds covering most of buccal cavity when closed; ischium subrectangular, with distinct median groove, surface with scattered pits and short setae; merus subquadrate, slightly wider than long, surface rugose, margins cristate, anteroexternal angle angular but not produced; exopod slender, reaching to about one-third length of merus, with elongate flagellum that reaches across width of merus (Fig. 3F).
Chelipeds asymmetrical, right larger ( Fig. 2A). Anterior margin of basis-ischium lined with small sharp granules; margins of merus lined with low sharp granules, appears weakly serrated. Outer surface of carpus rugose, inner distal angle with large sharp tooth and basal tooth ( Fig. 2A). Outer surfaces of chelae strongly rugose, upper part rugose with granules; major chela stouter, shorter than minor chela (Fig. 3H, I). Fingers of major chela short, stout, gently curved, subequal to palm, outer surface lined with 3 rows of pits; cutting edges of both fingers with variously sized sharp teeth and denticles; dorsal margin of dactylus with low tubercles and granules (Figs 2A, 3H). Fingers of minor chela similar to major chela in form but relatively more slender (Figs 2A, 3I).
Ambulatory legs short, segments relatively stout; second pair longest, last pair shortest ( Fig. 2A). Merus short, stout, outer surface rugose, dorsal margin uneven, subcristate, without subdistal spine or tooth; carpus rugose, dorsal margin with crista, outer surface with low submedian crista on first to third legs, that on fourth leg smooth; dorsal margin of propodus with crista, outer surface with low, submedian crista; dactylus relatively short, gently curved, quadrate in cross section, margins with short, sharp pectinate spines ( Fig. 2A).
Variation. The carapace tends to get less broad in smaller specimens and females (width to length ratio 1.26-1.30). The regions in smaller specimens is less sculptured (Fig. 2B, E) with the rugosities restricted mostly to lateral margins (Fig. 2C, G). The third maxilliped ischium is slightly longer in smaller individuals (Fig. 3G). The male pleon is proportionately less broad in smaller individuals with somite 6 more quadrate as they are smaller (Fig. 3C, D). In adult males, the G1 does not vary substantially although the cleft on the outer part of the distal section of the G1 subterminal segment is relatively less distinct (Fig. 4F). Smaller males (ca. 30 mm carapace width), however, not only have the G1 terminal segment relatively shorter and less curved, the cleft on the subterminal segment is also not discernible (Fig. 4H). The adult female has the pleon completely covering the thoracic sternum (Fig. 5A), the vulva is large, raised, ovate and positioned on the anterior half of sternite 6, pushing into the margin with sternite 5 (Fig. 5B).
Etymology. The species is named after Ms Khin Pyae Pyae Thaw Thar who collected the specimens used for this study. Her name is used here as a noun in apposition.
Colour. In life, the dorsal surfaces of the carapace and outer surfaces of the chelipeds are dark brown; with the ventral surfaces orangish-red; and the ambulatory legs are dark brown to orangish red (Fig. 1).
Habitat. The type locality, Malikha, is a fast-flowing river, the substrate consisting of rocks of various sizes, with the bank sandy. The banks are densely lined with tall trees. This river is a branch of the Ayeyarwady River (= Ayrwarwady River or Myitsone) and is about 43 km north of Myitkyina, the capital city of Kachin State.
Remarks. Five species of Indochinamon have been reported from and near Myanmar: I. andersonianum, I. edwardsii, I. hirtum, I. hispidum and I. tritum (cf. Alcock 1909Alcock , 1910Bott 1970;Yeo and Ng 2007). All these species were collected by John Anderson from the area east of Bhamo, mostly in the Kakhyen Hills (= Kachin Moun-  Adult male specimens of I. khinpyae have a strongly sculptured and very rough carapace (Fig. 2F), the G1 terminal segment is relatively long, gently curved, distally bent and the dorsal margin has no trace of a flap ( Fig. 4A-D, F, H). In I. andersonianum, even large males (50 mm carapace width) have the gastric regions relatively smooth with the rest of the surfaces also less rugose and granulose, and the male pleon is proportionately more narrow (Wood-Mason 1871: pl. 27 figs 16, 17, 20;Bott 1970: pl. 44 fig. 14;unpublished data). The G1 of I. andersonianum is also quite different with the terminal segment straight, slender and tapering towards the tip (Bott 1970: pl. 37 fig. 16). The taxonomy of I. andersonianum has been confused and many species previously referred to it have turned out to be other taxa (see Ng and Naiyanetr 1993). The figure of I. andersonianum by Alcock (1910: pl. 10 fig. 40) is actually a separate species, Potamiscus rangoonensis (Rathbun, 1904) (unpublished data). The G1 of the smaller paratype male of I. khinpyae (34.3×26.6 mm, ZRC 2018.0714) superficially resembles that of I. edwardsii (the type of which is about the same size) but in I. edwardsii, the anterolateral margins are prominently serrated even in smaller specimens (Wood-Mason 1871: pl. 27 figs 11, 12;Alcock 1910: pl. 14 fig. 43; unpublished data) (versus anterolateral margins finely granulated or weakly serrated in I. khinpyae; Fig. 2F, G); the upper part of the palm of the chela has many large tubercles (Wood-Mason 1871: pl. 27 figs 11, 14;Alcock 1910: pl. 14 . 69). Compared to I. hispidum, described from a male 43.0×31.0 mm from Ponsee, I. khinpyae can easily be distinguished by its more rugose dorsal carapace surface ( Fig. 2A . 4); and the male pleon is proportionately broader with the telson more broadly triangular (Fig. 3A, C, D) (versus male pleon more narrow with the telson acutely triangular in I. hispidum; cf. Wood-Mason 1871: pl. 27 fig. 5).
With regards to the other species of Indochinamon, they can be separated into several groups on the basis of their G1s. The type species, I. villosum, has a relatively short and stout G1 terminal segment which is gently bent and is conical to subconical in shape without an obvious dorsal flap, a character shared with I. ahkense, I. bavi, I. bhumibol, I. boshanense, I. changpoense, I. chinghungense, I. dangi, I. daweishanense, I. flexum, I. guttum, I. jianchuan, I. jinpingense, I. kimboiense, I. menglaense, I. mieni, I. orleansi, I. ou, I. parpidum, I. phongnha, I. tannanti, I. xinpingense, and I. yunlongense (including I. edwardsii and I. hispidum) (cf. Bott 1970;Yeo and Ng 1998;Dai 1999;Naruse et al. 2011Naruse et al. , 2018unpublished data). The other species have G1 terminal segments which are slender, elongate, and straight or curved; or relatively short and strongly bent (cf. Ng and Naiyanetr 1993;Dai 1999;Do et al. 2016;Naruse et al. 2018;unpublished data). The G1 of I. khinpyae closely resembles that of I. changpoense and I. daweishanense (both from Yunnan) but these two species have only a shallow cleft on the outer margin of the subdistal part of the subterminal segment, and the terminal segment is proportionately shorter and straighter (Dai 1999: figs 85-4, 5;87-4, 5), even though the types are comparable in size to the holotype of I. khinpyae. Similarly, I. yunlongense (described from a small male 19.0×16.1 mm from Yunnan) has a superficially similar G1 structure to I. khinpyae, except that the terminal segment is much straighter (Dai 1999: fig. 84-4, 5). The strongly sculptured and rugose carapace of large I. khinpyae allies it with large species like I. kimboense and I. bavi (both from Vietnam) but in these species, the cleft on the outer margin with of the G1 subterminal segment is shallow and not distinct (cf. Naruse et al. 2011: fig. 3a, b, d, e), even for specimens larger than the holotype of I. khinpyae, which has a prominent broad cleft ( Fig. 4A-D). The G1 terminal segment of I. kimboense and I. bavi (as well as I. cua, I. orleansi, I. ou and I. tannanti) are also distinctly tapering towards the tip (Naruse et al. 2011: fig. 3a, b, d, e), unlike the subtruncate condition in I. khinpyae (Fig. 4A-D). Compared to I. phongnha (from Vietnam), which also has the carapace regions distinct, the surfaces are smoother, notably the median and posterior parts which are smooth, even in large specimens (Naruse et al. 2011: fig. 7) (strongly rugose in large I. khinpyae; Figs 1A, 2A, F); and the G1, while it has a strong cleft on the outer margin of the subterminal segment, the terminal segment is sharply tapering (Naruse et al. 2011: fig. 9a, b) (terminal segment subcylindrical in large I. khinpyae; Fig. 4A-D). The strong cleft on the outer margin of the G1 subterminal segment of I. khinpyae is character also shared with I. cua from Thailand, but in this species, the cleft is relatively broader and the terminal segment is tapering distally (Yeo and Ng 1998: fig. 4B, C, E, G); and the carapace regions are proportionately much smoother (Yeo and Ng 1998: fig. 7A). In I. lipkei from Thailand, the dorsal carapace surface, even in large specimens, is less well marked with the median parts much less rugose (Ng and Naiyanetr 1993: fig. 12A); pleonal somite 6 is distinctly trapezoidal in shape (Ng and Naiyanetr 1993: fig . 12C); and the G1 terminal segment is strongly bent at about 60° along the longitudinal axis (Ng and Naiyanetr 1993: fig. 47B-E) (versus the dorsal carapace regions are more rugose, pleonal somite 6 is weakly trapezoidal, and the G1 terminal segment is bent at about 45° in I. khinpyae; Figs 2F, 3A, C, D, 4A-D).
Indochinamon khinpyae is not known to be threatened by any developments, and the forests and streams where it has been found are isolated and not easily assessible by man. As such, the species is classified under taxa of Least Concern for the moment (cf. Cumberlidge et al. 2009Cumberlidge et al. , 2012. A note on I. manipurense (Alcock, 1909) is necessary. Takeda et al. (2012: 207) noted that specimens they had of this species did not possess a flagellum on the exopod of the third maxilliped, and as such, the species should be transferred to Potamiscus Alcock, 1909. However, the types of this species do have a flagellum (Yeo and Ng 2007;unpublished data), so Takeda et al.'s (2012) specimens will need to be checked to ascertain their identity. As such, for the moment, we retain the species in the genus Indochinamon.