Indochinamon malipoense Zhang & Sun, 2020

Zhang, Zewei, Pan, Da, Hao, Xiyang & Sun, Hongying, 2020, Two new species of freshwater crabs of the genera Eosamon Yeo & Ng, 2007 and Indochinamon Yeo & Ng, 2007 (Crustacea, Brachyura, Potamidae) from southern Yunnan, China, ZooKeys 980, pp. 1-21 : 1

Indochinamon malipoense Zhang & Sun sp. nov. Figs 7 , 8 , 9 , 10

Material examined.

Holotype: China • 1 male, 53.0 × 42.7 mm, NNU 180505; Yunnan Province, Wenshan Prefecture, Malipo County, Tianbao Town, Bajiaoping Village; 22°58'53"N, 104°50'27"E; 1075 m a.s.l.; 5 April 2018; leg. Zhan Zhang, Zewei Zhang & Hongying Sun. Paratypes: China • 1 female, 48.0 × 38.2 mm, NNU 180603; Yunnan Province, Wenshan Prefecture, Malipo County, Babu Town; 23°13'29"N, 104°54'04"E; 550 m a.s.l.; 6 April 2018, leg. Zhan Zhang, Zewei Zhang & Hongying Sun • 2 males, 63.2 × 49.0 mm, NNU 180501, 60.5 × 48.0 mm, NNU 180506, same data as holotype.

Comparative material.

Indochinamon changpoense Dai, 1995: China • 1 male, 44.1 × 35.6 mm, NNU 161701; Yunnan Province, Jinping County Changpotou; 17 May 2016; leg. Kelin Chu, Pengfei Wang & Hongying Sun; Indochinamon tannanti Rathbun, 1904: China • 1 male, 43.3 × 34.9 mm, NNU 180801; Yunnan Province, Hekou County; 8 April 2018; leg. Zhan Zhang, Zewei Zhang & Hongying Sun.

Diagnosis.

Carapace broader than long, dorsal surface glabrous, gently convex; regions indistinctly defined; anterolateral margin lined with obvious granules (Fig. 7A ). Third maxilliped exopod with flagellum (Fig. 8A ). Male pleon triangular, lateral margin of sixth somite distinctly convex; telson triangular, tip rounded (Fig. 7C ); G1 terminal segment distinctly curved, subterminal segment about 3.2 times as long as terminal segment (Fig. 8B, C ); G1 strongly curved outwards, not reaching pleonal locking mechanism in situ (Fig. 8E ). Female pleon ovate (Fig. 9A ), vulvae on thoracic sternite 6, subrotund, opening inner, ventrolateral margin arched distinctly (Fig. 9B ).

Description.

Carapace about 1.2 - 1.3 times broader than long (N = 4), subtrapezoidal, dorsal surface gently convex, glabrous; anterolateral region lined with granules, border with spinose granulation (Fig. 7A ); cervical groove shallow, inconspicuous; H-shaped groove between gastric and cardiac regions shallow but distinct (Fig. 7A ). Front slightly deflexed, with anterior border emarginated medially (Fig. 7A, B ); postfrontal lobe distinctly convex, separated medially by Y-shaped groove; postorbital cristae obviously convex, separated from postfrontal lobe by distinct groove (Fig. 7A ); postorbital region distinctly concave (Fig. 7A, B ). Posterolateral margin comparatively smooth with few rugae; branchial regions relatively flat, smooth (Fig. 7A ). External orbital angle acutely triangular; epibranchial tooth with sharp protuberance, separated from external orbital angle by distinct cleft (Fig. 7A ). supraorbital, infraorbital margins cristate; pterygostomial regions comparatively smooth with several granules (Fig. 7B ). Epistome superior margin cristate, inferior margin slightly curved with median triangle (Fig. 7B ).

Ischium of third maxilliped elongate rectangular, about 1.3 times longer than broad, with distinct, longitudinal median sulcus; merus trapezoidal, about 1.1 times broader than long; exopod reaching beyond base of merus slightly, with short flagellum, about half the width of the merus (Fig. 8A ).

Chelipeds unequal (Fig. 7A ); merus margins crenulated (Fig. 7C ); carpus with sharp spine at inner-distal angle, spinules and granules at base (Fig. 7A ); outer surface of manus with convex granules, about 1.3 times as long as high; immovable, movable fingers curved inwards, with irregular teeth; gape narrow when fingers closed (Fig. 7D ).

Ambulatory legs relatively slender, dactylus slender, with spine-like setae (Fig. 7A ); second ambulatory leg merus about 1.8 times as long as dactylus; last leg with propodus about 2.7 times as long as broad, slightly shorter than dactylus (Fig. 7A ).

Thoracic sternum glabrous, sternites 1, 2 completely fused to form triangular structure; suture between sternites 2, 3 distinct (Fig. 7C ); suture between sternites 3, 4 shallow (Fig. 7C ); sterno-pleonal cavity reaching anteriorly to level of mid-length of cheliped coxae bases, median longitudinal groove between sternites 7, 8 long (Fig. 8E ). Male pleon triangular, third somite widest; sixth somite width 2.0 times length; telson triangular, width 1.4 times length, tip of telson round (Fig. 7C ). Female pleon ovate, smooth, pitted; sixth somite about 2.9 times as broad as long, telson semicircular, about 2.2 times as broad as long (Fig. 9A ).

G1 stout, bent; tip of terminal segment not reaching pleonal locking mechanism in situ (Fig. 8E ); subterminal segment stout, about 3.2 times as long as terminal segment (Fig. 8B, C ); terminal segment slender, unciform, clearly curved outwards, inferior and superior margins curved (Fig. 8E, F ); base of G1 terminal segment slightly inflated, distal part tapered (Fig. 8F ); G2 distinctly longer than G1, subterminal segment about 1.2 times as long as terminal segment (Fig. 8D ). Female vulvae on thoracic sternite 6, ovate, opening inwards towards median of cavity, vulvar cover margin slightly arched (Fig. 9B ).

Live coloration

. The crabs usually have two colors: brownish-red (Fig. 11A ) and yellowish-cyan (Fig. 11B ). From the type locality, Tianbao Town, both brownish-red and yellowish-cyan crabs have been found, while from Babu Town, only yellowish-cyan crabs have been found. Morphologically, there is no distinct difference between individuals with different colors. Similar color variation also can be seen in another potamid crab, Geothelphusa pingtung Tan & Liu, 1998 ( Shy et al. 2019).

Etymology.

This species is named after the type locality, Malipo County, Yunnan Province, China.

Remarks.

Based on the morphology of G1, Ng and Mar (2018) separated Indochinamon into several groups. The G1 terminal segment of I. malipoense sp. nov. is similar to a large group including the type species, I. villosum (Yeo & Ng, 1998). Within this group, I. malipoense sp. nov. closely resembles I. ahkense Naruse, Chia & Zhou, 2018, I. bavi Naruse, Nguyen & Yeo, 2011, I. changpoense (Dai, 1995), I. daweishanense (Dai, 1995), I. kimboiense Naruse, Nguyen & Yeo, 2011, I. orleanis (Rathbun, 1904), I. ou (Yeo & Ng, 1998), I. parpidum Naruse, Chia & Zhou, 2018, I. tannanti (Rathbun, 1904) and I. yunlongense (Dai, 1995), as their G1s are gently bent and G1 terminal segments are relatively slender and elongate (cf. Yeo and Ng 1998; Dai 1999; Naruse et al. 2011, 2018; Ng and Mar 2018). But I. malipoense sp. nov. can be distinguished from other species by the obviously curved G1 terminal segment.

All Indochinamon species have a well-developed flagellum on the exopod of the third maxilliped. The length of the flagellum varies among species. In some species, the flagellum does not exceed the width of the merus, e.g., I. tannanti , I. changpoense , I. gengmaense (Dai, 1995), I. guttus (Yeo & Ng, 1998), I. hispidum (Wood-Mason, 1871), I. jinpingense , I. mieni (Dang, 1967) and I. yunlongense . In I. malipoense sp. nov., the flagellum is about half the width of the merus, which is shorter than that in other species.

The G1 of I. malipoense sp. nov. is very similar to I. tannanti , I. changpoense , I. ahkense , and I. daweishanense . They are also geographically close. But I. malipoense sp. nov. can be distinguished from the similar I. tannanti and I. changpoense by several characters (Table 3 ), notably, the carapace regions are indistinctly defined (Fig. 7A ) (versus distinctly defined in I. tannanti and I. changpoense ( Dai 1999)), the G1 terminal segment is obviously curved, unciform (Fig. 10A ) (versus slightly curved, conical in both I. tannanti and I. changpoense , Fig. 10B, C )), the base of the G1 terminal segment is slightly inflated (Fig. 8F ) (versus nearly straight in both I. tannanti and I. changpoense , Fig. 10B, C ). The G1 structure of I. malipoense sp. nov. is also similar to I. ahkense ( Naruse et al. 2018: fig. 4) and I. daweishanense ( Dai 1999: fig. 87) by relatively slender terminal segment. However, the G1 terminal segment is more curved in I. malipoense sp. nov. and stronger bent outward in I. daweishanense . The carapace of I. malipoense sp. nov. is superficially similar to I. ahkense by smooth and shallow grooves of the dorsal surface. In I. ahkense , the carapace is subquadrate (versus subtrapezoidal in I. malipoense sp. nov.) and flatter (versus slightly convex in I. malipoense sp. nov.).

In I. khinpyae , the carapace and G1 show considerable variations ( Ng and Mar 2018). In smaller individuals, the carapace is less sculptured and the G1 terminal segment is shorter and straighter ( Ng and Mar 2018). In I. malipoense sp. nov., the morphology of the carapace is relatively stable while the ratio of G1 subterminal segment to terminal segment varies in sampled individuals.

Distribution and habitat.

Indochinamon malipoense sp. nov. was collected from Tianbao Town (22°58'53"N, 104°50'27"E, 1075 m a.s.l.; 22°56'58"N, 104°49'48"E, 223 m a.s.l.; 23°00'07"N, 104°47'42"E, 979 m a.s.l.) and Babu Town (23°13'29"N, 104°54'04"E, 550 m a.s.l.) located in the frontier between China and Vietnam, Malipo County, Wenshan Prefecture in Yunnan, China. They were found under rocks in mountain streams with altitudes of 200-1100 m.

Indochinamon ahkense , I. changpoense , I. daweishanense , I. jinpingense , I. tannanti and Somanniathelphusa brevipodum Tai, Song, He, Cao, Xu & Zhong, 1975, have been recorded near the distribution areas of I. malipoense sp. nov..

Figures

Figure 7. Indochinamon malipoense sp. nov. holotype, male, 53.0 x 42.7 mm, NNU 180505 A dorsal view B frontal view of cephalothorax C ventral view showing anterior thoracic sternum and pleon D outer surfaces of left major chela. Scale bars: 1.0 cm.

Figure 8. Indochinamon malipoense sp. nov. holotype, male, 53.0 x 42.7 mm, NNU 180505 A left third maxilliped B left G 1 (ventral view) C left G 1 (dorsal view) D left G 2 E sterno-pleonal cavity with right G 1 in situ F left G 1 terminal segment (ventral view). Scale bars: 1.0 mm.

Figure 9. Indochinamon malipoense sp. nov. paratype, female, 48.0 x 38.2 mm, NNU 180603 A abdomen B vulvae.

Figure 10. The ventral view of left G 1 A Indochinamon malipoense sp. nov. holotype, male, 53.0 x 42.7 mm, NNU 180505 B Indochinamon tannanti male, 43.3 x 34.9 mm, NNU 180801 C Indochinamon changpoense male, 44.1 x 35.6 mm, NNU 161701. Scale bars: 1.0 mm.

Figure 11. Color in life of Indochinamon malipoense sp. nov. A brownish-red male B yellowish-cyan male. Photographs by Hongying Sun, 5 April 2018, Tianbao Town, Yunnan Province, China.