Lobothelphusa bagoensis, Shi & Chen & Sun, 2022

Shi, Boyang, Chen, Xiaoyong & Sun, Hongying, 2022, On two new species of the genus Lobothelphusa Bouvier, 1917 (Decapoda: Brachyura: Potamidae: Potaminae) from the Pegu Range, central Myanmar, Raffles Bulletin of Zoology 70, pp. 65-79 : 67-71

Lobothelphusa bagoensis , new species

( Figs. 2 , 3 , 6A–C , 7A–D )

Material examined. Holotype: adult male (cw 39.72 mm, cl 31.98 mm, ch 20.34 mm, fw 13.68 mm), NNU16-DYX1, Taungoo Township , Pegu Range, Bago Division, 18.857°N, 96.103°E, 233 m asl, Myanmar ( Fig. 1 dark blue), coll. B. Shi, 13 May 2019.

Paratypes: adult male (cw 37.38 mm, cl 30.48 mm, ch 20.86 mm, fw 12.32 mm), NNU16-DYX2, and adult female (cw 36.18 mm, cl 30.72 mm, ch 19.62 mm, fw 12.68 mm), SEABRI-DYX3, same location as holotype.

Other material: adult female (cw 37.29 mm, cl 29.67 mm, ch 19.94 mm, fw 12.47 mm), NNU16-AG2; adult female (cw 38.45 mm, cl 30.54 mm, ch 20.94 mm, fw 12.88 mm), NNU16-AG3; adult female (cw 37.67 mm, cl 29.97 mm, ch 20.03 mm, fw 12.76 mm), SEABRI-AG4; adult female (cw 39.42 mm, cl 31.28 mm, ch 21.34 mm, fw 13.52 mm), SEABRI-AG5; Oktwin Township , Bago Division, 18.789°N, 96.439°E, 38 m asl, Myanmar, coll. B. Shi, 8 May 2019 .

Description. Carapace subtrapezoidal, distinctly broader than long (cw/cl = 1.23; ch/cl = 0.68); dorsal surface smooth, slightly convex longitudinally and transversely; regions indistinct, cervical grooves poorly developed, shallow, H-shaped groove well-developed ( Fig. 2A ). Epigastric cristae low, distinct, gently rugose, separated by groove which opens up into inverted Y-shaped gap posteriorly, positioned anterior to postorbital cristae, separated from postorbital cristae by distinct narrow groove; postorbital cristae distinct but low, straight, sharp, confluent with the first epibranchial teeth; regions behind epigastric and postorbital cristae smooth ( Fig. 2A ). Frontal margin almost straight or gently concave (fw/ cw = 0.38), with very low, rounded granules; frontal region relatively broad longitudinally ( Fig. 2A ). Antennular fossae rectangular when viewed from front; supraorbital margin sinuous, cristate; infraorbital margin sinuous, slightly sloping downward, cristate; orbital region relatively broad; suborbital, pterygostomial regions granulose; eyes filling up most of orbital space; eyestalk short, stout; cornea moderately large, pigmented ( Fig. 2C ). External orbital angle well-developed, triangular, tip acute, outer margin distinctly convex, with deep cleft separating it from anterolateral margins; anterolateral margins convex, each with four prominent epibranchial teeth; epibranchial teeth stout, teeth 1–4 progressively smaller, tips directed anterolaterally, base of each tooth broad; posterolateral margin sinuous; posterior carapace margin convex; branchial region with very weak, oblique striae ( Fig. 2A ). Posterior margin of epistome with welldeveloped median tooth, lateral margins sinuous ( Fig. 2C ). Third maxilliped glabrous; ischium subtrapezoidal, ca. 0.61 times width of length, elongate longitudinally, without median sulcus; merus subrectangular, ca. 1.76 times width; exopod reaching two-thirds length of merus, with well-developed flagellum ( Figs. 2B–D , 3C ).

Chelipeds asymmetric, glabrous, major chela distinctly larger; dorsal surface smooth; merus with well-developed subdistal spine on dorsal margin; carpus with strong, welldeveloped spine on inner distal angle, spine slightly sinuous ( Fig. 2A–D ). Palm of major chela longer than high, inner and outer surfaces inflated, punctate; fingers of major chela punctate, with numerous teeth of different size, large gape when finger closed, fingers slightly curved, equal in length to palm; minor cheliped similar to major cheliped ( Fig. 3A ).

Ambulatory legs relatively long, slender, p3 longest, p5 shortest, outer margins heavily setose; p5 propodus relatively stouter than p2–p4 propodi; dactylus slightly curved, equal in length to propodus, with short, sharp chitinous spines on margins; outer edges with thick spongy tomentum ( Figs. 2A, B, D , 3B ).

Male thoracic sternum smooth; thoracic sternites s1/s2 completely fused; suture thoracic sternites s2/s3 distinct; thoracic sternites s3/s4 fused, groove between sternites not discernible; sutures between thoracic sternites s4/s5, s5/s6, s6/s7 shallow, narrow; suture between thoracic sternites s7/ s8 distinct ( Fig. 2B, E ). Pleonal locking mechanism with distinct, anteriorly directed tubercle on submedian part of sternite s5 ( Fig. 2G ). Narrow transverse ridge at the suture between thoracic sternites s7/s8 that interrupts the median line ( Fig. 2G, H ).

Male pleon narrowly triangular; telson with blunt apex and concave lateral margins, ca. 0.70 times length of width; somite 6 subrectangular, ca. 1.95 times length of width, lateral margins gently convex or straight; somites 4–6 trapezoidal, progressively less broad; lateral margins of segment 3 distinctly convex; lateral margins of somites 4 and 5 gently concave; suture between somites 5/4, 4/3 distinctly sinuous; somite 3 broader than somites 1 and 2 longitudinally; somite 2 longitudinally broader than somite 1; somite 1 longitudinally narrow ( Fig. 2B, E ). Female pleon ovate, covering the thoracic sternites when closed; telson broadly subtriangular, much broader than long, with convex lateral margins; somites 4–6 almost equal, broader than long, with convex lateral margins; somites 1–3 progressively longer ( Fig. 2D, F ).

G1 gently sinuous or straight, slender, tip of terminal segment not reaching pleonal locking mechanism in situ ( Figs. 2G , 3D, E , 6A, B ); groove for G2 on ventral surface; terminal segment short, conical in shape, straight, tip acute, distal part gently curved outward or straight, ca. 0.23 times length of subterminal segment; dorsal fold low, extending along proximal portion to three-quarters length of terminal segment; subterminal segment convex on upper part of inner margin ( Figs. 3D, E , 6A, B ). G2 length equal to length of G1; distal segment long, ca. 0.41 times length of basal segment ( Figs. 3F , 6C ). Vulvae on thoracic sternite 6, relatively small, subtriangular, occupying ca. 0.45 times length of thoracic sternite 6, almost reaching suture between thoracic sternites s4/s5 ( Fig. 2H ).

Etymology. The new species is named after the administrative region in which the type locality is situated, Bago Division, Myanmar.

Colour in life. In life, the adult animals are pale yellow with numerous reddish-brown spots dorsally, with the ventral surfaces pearly white. The ambulatory legs are pale yellow as on the carapace, but the basal parts are often pearl white. The thick spongy tomentum of the ambulatory legs is usually brownish yellow. The tips of the dactyli of the ambulatory legs are whitish-yellow. The integument at the articulations between the chela carpus and merus in the chelipeds is white ( Figs. 2 , 7C, D ).

Ecological note. These specimens were obtained from streams in hilly terrain and were dug out from mud burrows approximately 60–80 cm deep in well-drained, silty soil along the riparian zone ( Fig. 7A ). The eggs from three female individuals (NNU16-AG2, NNU16-AG3, SEABRI-AG4) were observed to be a bright yellow in colour and small in size (1.5–2.0 mm diameter) ( Fig. 7B ), and with each female carrying 253– 374 eggs.

Remarks. Lobothelphusa bagoensis , new species, most closely resembles congeners L. crenulifera (Wood-Mason, 1875) and L. calva (Alcock, 1909) in the general carapace features. The new species, however, differs markedly in the following: (1) the anterolateral and posterolateral margins are convex and the frontal margin is almost straight ( Fig. 2A ) (versus the anterolateral and posterolateral margins are slightly convex, and the frontal margin is slightly concave in L. crenulifera and L. calva , cf. Alcock, 1910: pl. 4, fig. 13; Bott, 1970: pls. 45–46, figs. 21, 22; Rathbun, 1905: pl. 12, fig. 11); (2) the frontal region is relatively broad longitudinally ( Fig. 2A ) (versus the frontal region relatively narrow longitudinally in L. crenulifera and L. calva , cf. Alcock, 1910: pl. 4, figs. 13, 14; Bott, 1970: pls. 45–46, figs. 21, 22; Rathbun, 1905: pl. 12, fig. 11); (3) the postorbital cristae are almost horizontal ( Fig. 2A ) (versus the postorbital cristae are slightly oblique in L. crenulifera and L. calva , cf. Alcock, 1910: pl. 4, figs. 13, 14; Bott, 1970: pls. 45–46, figs. 21, 22; Rathbun, 1905: pl. 12, fig. 11); (4) the G1 is gently sinuous or straight, the distal part of the terminal segment is curved outward ( Figs. 3D, E , 6A, B ) (versus the G1 is sinuous, the distal part is strongly curved outward in L. crenulifera and L. calva , cf. Bott, 1970: pl. 38, figs. 23, 24); (5) the dorsal flap extends along the proximal portion to three-quarters of the length of the terminal segment ( Figs. 3D, E , 6A, B ) (the dorsal flap extends to half or two-thirds of the terminal segment in L. crenulifera , cf. Bott, 1970: pl. 45, fig. 21); and (6) the subterminal segment is convex on the upper part of the inner margin ( Figs. 3D, E , 6A, B ) (versus the subterminal segment is slightly concave on the upper part of inner margin in L. crenulifera , cf. Bott, 1970: pl. 45, fig. 21; the subterminal segment is distinctly concave on the upper part of inner margin in L. calva , cf. Bott, 1970: pl. 46, fig. 22).

Lobothelphusa bagoensis , new species, is less likely to be confused with Lobothelphusa barbouri ( Rathbun, 1910) , although these congeners do share superficial resemblance in some aspects of the carapace ( Fig. 2A ). The new species, however, can easily be separated from L. barbouri by the flat carapace with shallow cervical grooves, the outer margin of the external orbital angle being distinctly convex, and the epibranchial teeth being stouter with broader bases (versus the inflated carapace with relatively deeper cervical grooves, the outer margin of the external orbital angle being nearly straight or slightly concave, and the epibranchial teeth being relatively more slender with narrower bases in L. barbouri , cf. Rathbun, 1910: pl. 5, figs. 1, 2).

Lobothelphusa bagoensis , new species, is unlikely to be confused with Lobothelphusa woodmasoni ( Rathbun, 1905) . The latter is reportedly distributed in northern Myanmar and India ( Rathbun, 1905; Bott, 1970). The new species can be easily distinguished from L. woodmasoni by its indistinct carapace regions, straight or gently concave frontal margin ( Fig. 2A ) (versus the carapace regions are distinct, frontal margin is concave in L. woodmasoni , cf. Rathbun, 1905: pl. 12, fig. 12; Bott, 1970: pl. 38, fig. 25), and the G1 terminal segment which is conical in shape, with the distal part slightly curved outward, and the pronounced dorsal fold extending to three-quarters length of the terminal segment ( Figs. 2A , 3D, E , 6A, B ) (versus the G1 terminal segment is narrowly conical in shape, with the distal part slightly curved inward, and without a dorsal fold in L. woodmasoni , cf. Bott, 1970: pl. 46, fig. 23).

Figures

Fig. 2. Lobothelphusa bagoensis, new species. A–C, E, G, holotype, male, 39.72 × 31.98 mm, NNU16-DYX1; D, F, H, paratype, female, SEABRI-DYX3, 36.18 × 30.72 mm. A, dorsal view; B, D, ventral views; C, frontal view; E, F, ventral view showing anterior thoracic sternum and pleon; G, ventral view showing sterno-pleonal cavity with G1 in situ; H, thoracic sternum and vulvae. Scale bars = 1.0 cm.

Fig. 3. Lobothelphusa bagoensis, new species, holotype, male, NNU16-DYX1. A, major chela (dorsal view); B, right third ambulatory leg (dorsal view); C, left third maxilliped (dorsal view); D, left G1 (dorsal view); E, left G1 (ventral view); F, left G2 (ventral view). Scale bars: A–C = 1.0 cm; D–F = 1.0 mm.

Fig.6. Gonopods.A–C, Lobothelphusa bagoensis, new species, holotype, male, NNU16-DYX1; D–F, Lobothelphusa thewanica, new species, holotype, male, NNU16-BG1. A, D, left G1 (ventral view); B, E, left G1 (dorsal view); C, F, left G2 (ventral view). Scale bars = 1.0 mm.

Fig. 7. Habitat and live colouration. A–D, Lobothelphusa bagoensis, new species: A, habitat; B, paratype, ovigerous female (SEABRI- DYX3); C, D, holotype, male (NNU16-DYX1). E–G, Lobothelphusa thewanica, new species: E, habitat; F, G, holotype, male (NNU16-BG1).

Fig. 1. Sampling sites for Lobothelphusa bagoensis, new species (dark blue), Lobothelphusa thewanica, new species (light blue), and Paratelphusula gibbosa Ng & Kosuge, 1997 (yellow) in Myanmar.