Lobothelphusa thewanica, 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 : 71-74

Lobothelphusa thewanica , new species

( Figs. 4 , 5 , 6D–F , 7E–G )

Material examined. Holotype: adult male (cw 31.44 mm, cl 26.14 mm, ch 15.38 mm, fw 10.96 mm), NNU16-BG1, Thewa Township , Pegu Range, Bago Division, 18.492°N, 96.387°E, 53 m asl, Myanmar ( Fig. 1 light blue), coll. B. Shi, 11 May 2019.

Paratypes: adult male (cw 32.84 mm, cl 26.88 mm, ch 15.68 mm, fw 11.12 mm), NNU16-BG2; adult female (cw 29.26 mm, cl 25.69 mm, ch 14.73 mm, fw 11.24 mm), SEABRIBG3; adult male (cw 30.26 mm, cl 24.13 mm, ch 14.44 mm, fw 9.13 mm), SEABRI-BG4; juvenile (cw 28.61 mm, cl 23.57 mm, ch 13.67 mm, fw 8.78 mm), SEABRI-BG5; juvenile (cw 28.31 mm, cl 23.22 mm, ch 13.32 mm, fw 8.52 mm), SEABRI-BG6; Same location as holotype.

Description. Carapace subquadrate, slightly broader than long (cw/cl = 1.20; ch/cl = 0.58); dorsal surface smooth, gently swollen longitudinally and transversely; regions indistinct, cervical grooves developed, shallow, H-shaped groove well-developed ( Fig. 4A ). Epigastric cristae low, distinct, slightly rugose, separated by groove which opens up into inverted Y-shaped gap posteriorly, distinctly positioned anterior to postorbital cristae, separated from postorbital cristae by distinct narrow groove; postorbital cristae distinct, sinuous, slightly oblique, sharp, confluent with the first epibranchial teeth; regions behind epigastric and postorbital cristae smooth ( Fig. 4A ). Frontal margin slightly concave (fw/cw = 0.38), with very low, rounded granules; frontal region broad longitudinally ( Fig. 4A ). Antennular fossae rectangular when viewed from front; supraorbital margin sinuous, cristate; infraorbital margin sinuous, sloping downward, cristate; orbital region relatively broad; suborbital and pterygostomial regions granulose; eyes filling up most of orbital space; eyestalk short, stout; cornea moderately large, pigmented ( Fig. 4C ). External orbital angle well-developed, triangular, tip acute, outer margin convex, margins cristate, with deep cleft separating it from anterolateral margins; anterolateral margins gently convex, each with four prominent epibranchial teeth; epibranchial teeth 1–4 progressively smaller, tips directed anterolaterally, base of each tooth slightly broad; first and second epibranchial teeth distinctly broader; third and fourth epibranchial teeth slender; posterolateral margin sinuous; posterior carapace margin gently convex or straight; branchial region without oblique striae ( Fig. 4A ). Posterior margin of epistome with well-developed, triangular median tooth, lateral margins straight ( Fig. 4C ). Third maxilliped glabrous; ischium of third maxilliped rectangular, elongate longitudinally, ca. 0.65 times length of width, without median sulcus; merus squarish, ca. 1.52 times length of width; exopod reaching half-length of merus, with well-developed flagellum ( Figs. 4B, C , 5A ).

Chelipeds asymmetrical, 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; inner distal angle sinuous ( Fig. 4A–C ). Fingers of major chela with numerous teeth of different size, large gape when finger closed; fingers of minor chela similar to major chela; fingers slightly curved, equal in length to palm; palm longer than high; inner and outer surfaces inflated ( Fig. 4A–D ).

Ambulatory legs relatively long, slender, p3 longest, p5 shortest; 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 ( Fig. 4A, B, E ).

Male thoracic sternum smooth; thoracic sternites s1/s2 completely fused; suture between 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, s7/s8 shallow, narrow ( Fig. 4B, F, H ). Pleonal locking mechanism with distinct, anteriorly directed tubercle on submedian part of sternite s5 ( Fig. 4H ). Narrow transverse ridge at the suture between thoracic sternites s7/ s8 that interrupts the median line ( Fig. 4H, I ).

Male pleon narrowly triangular; telson with blunt apex and concave lateral margins, ca. 0.79 times length of width; somite 6 trapezoidal, ca. 2.12 times length of width, lateral margins straight; somites 4–6 trapezoidal, progressively less broad; lateral margins of somites 4–6 straight; lateral margins of somite 3 distinctly convex; 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. 4B, F ); Female pleon ovate, covering the thoracic sternites when closed; telson broadly subtriangular, much broader than long, with slightly convex lateral margins; somites 5 longest, broader than long, with convex lateral margins; somites 4 and 6 almost equal; somites 1–3 progressively longer ( Fig. 4G ).

G1 slightly sinuous, slender, tip of terminal segment situated adjacent to pleonal locking structure in situ ( Figs. 4H , 5B, C , 6D, E ); groove for G2 on ventral surface; terminal segment relatively short, conical in shape, tip acute, distal part slightly curved outward, ca. 0.29 times length of subterminal segment; dorsal fold relatively high, extending along one-quarter to three-quarters of terminal segment, with rounded apex in medial position; subterminal segment gently convex on upper part of inner margin ( Figs. 5B, C , 6D, E ). G2 length equal to length of G1; distal segment long, ca. 0.48 times length of basal segment ( Figs. 5D , 6F ). Vulvae on sternite 6, semicircular, occupying ca. 0.50 times the length of the thoracic sternite 6, almost reaching suture between thoracic sternites s4/s5 ( Fig. 4I ).

Etymology. The species is named after the type locality, the township of Thewa, in the Pegu Range, Bago Division, Myanmar.

Colour in life. The adult animals are olive green dorsally with the ventral surfaces yellow. The chelipeds and ambulatory legs are pale yellow. The black colouration seen in the photographs is due to the black sediment that has strongly adhered to the exoskeleton. The thick spongy tomentum of the ambulatory legs is usually brown ( Figs. 4 , 7F, G ).

Ecological note. Individuals were collected under stones and the layers of fallen leaves in the river or on its banks; the substrate consists mainly of stones and rocky rubble ( Fig. 7E ). Remarks. The new species fits well within the morphological definition of the genus Lobothelphusa , particularly the flat carapace with indistinct dorsal regions, the third maxilliped ischium without a median sulcus, and the anterior margins of the ambulatory carpi, propodi, and dactyli with a thick spongy tomentum. Lobothelphusa thewanica , new species, is similar to L. bagoensis , new species, and L. crenulifera in the morphology of the postorbital cristae and the G1, but markedly distinct in some characters: (1) the carapace is subquadrate, the outer margin of the external orbital angle is convex, the epigastric cristae are positioned distinctly anterior to the postorbital cristae, and the third and fourth epibranchial teeth are slender ( Fig. 4A ) (versus the carapace is subtrapezoidal, the epigastric cristae are gently anterior or parallel to the postorbital cristae, and the third and fourth epibranchial teeth are stout in L. bagoensis and L. crenulifera , Fig. 2A , cf. Rathbun, 1905: pl. 12, fig. 11; Bott, 1970: pl. 38, fig. 23, pl. 45, fig. 21; the outer margin of the external orbital angle is more pronouncedly convex in L. bagoensis , Fig. 2A ); (2) the G1 is slightly sinuous, with the terminal segment proportionately longer, ca. 0.29 times length of the subterminal segment, and the distal part is slightly curved outward ( Figs. 5B, C , 6D, E ) (versus the G1 is gently sinuous or straight, the terminal segment is relatively short, ca. 0.23 times length of the subterminal segment, and the distal part is gently curved outward in L. bagoensis , Figs. 3D, E , 6A, B ; whereas the G1 is sinuous, the terminal segment is relatively short, ca. 0.21 times length of the subterminal segment, and the distal part is curved outward in L. crenulifera , cf. Bott, 1970: pl. 38, fig. 23); (3) the dorsal fold of the G1 terminal segment is relatively high, and extends along a quarter to three-quarters of the length of the terminal segment (versus the dorsal fold is low in L. bagoensis and L. crenulifera , Figs. 3D, E , 6A, B , cf. Bott, 1970: pl. 38, fig. 23; the dorsal fold extends to three-quarters of the length of the terminal segment in L. bagoensis , Figs. 3D, E , 6A, B ); and (4) the G1 subterminal segment is slender, the upper part of the inner margin is gently convex (versus the upper part of the inner margin is convex in L. bagoensis , Figs. 3D, E , 6A, B ; the upper part of the inner margin is slightly concave in L. crenulifera , cf. Bott, 1970: pl. 38, fig. 23).

Figures

Fig. 4. Lobothelphusa thewanica, new species. A–F, H, holotype, male, 31.44 × 26.14 mm, NNU16-BG1; G, I, paratype, female, 32.84 × 26.88 mm, NNU16-BG2. A, dorsal view; B, ventral view; C, frontal view; D, major chela (dorsal view); E, right third ambulatory leg (dorsal view); F, G, ventral view showing anterior thoracic sternum and pleon; H, ventral view showing sterno-pleonal cavity with G1 in situ; I, thoracic sternum and vulvae. Scale bars = 1.0 cm.

Fig. 5. Lobothelphusa thewanica, new species, holotype, male, NNU16-BG1. A, left third maxilliped (dorsal view); B, left G1 (dorsal view); C, left G1 (ventral view); D, left G2 (ventral view). Scale bars: A = 1.0 cm; B–D = 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.

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.