Esanthelphusa kayinensis, Shi, Boyang, Chen, Xiaoyong, Pan, Da & Sun, Hongying, 2021

Shi, Boyang, Chen, Xiaoyong, Pan, Da & Sun, Hongying, 2021, First record of the freshwater crab genus Esanthelphusa Naiyanetr, 1994 (Decapoda: Brachyura: Gecarcinucidae) from Myanmar, with the description of a new species from the Kayin State, Journal of Natural History 55 (35 - 36), pp. 2299-2312 : 2301-2310

Esanthelphusa kayinensis sp. nov.

( Figures 2–4 )

Material examined

Holotype male (adult), 31.58 × 25.34 mm, NNU16C-PA1, Hpa-An Township, Kayin State, Myanmar, 17.041°N, 97.755°E, 23.5 m altitude, coll. Boyang Shi, 4 May 2019.

Paratypes

Female (adult), 29.65 × 24.49 mm, NNU16C-PA2; male (adult), 29.26 × 23.98 mm, SEABRIPA3; same data as holotype.

Diagnosis

Carapace subhexagonal; dorsal surface strongly inflated; regions indistinct; cervical grooves narrow and shallow, not reaching level of postorbital cristae; H-shaped grooves distinct. Anterolateral margins convex, with three prominent epibranchial teeth ( Figure 2 (a)). Epigastric cristae well developed, sharp; postorbital cristae developed, rugose, straight ( Figure 2 (a)). External orbital angle broadly triangular, outer margin gently convex ( Figure 2 (a)). Frontal margin almost straight, cristate ( Figure 2 (a)). Supraorbital and infraorbital margins sinuous, subcristate; orbital region relatively broad ( Figure 2 (c)). Suborbital and pterygostomial regions partly with strong granules ( Figure 2 (c)). Epistome anterior margin with low median triangle ( Figure 2 (c)). Eyes relatively small compared to orbital space ( Figure 2 (c)). Antennular fossae rectangular in frontal view ( Figure 2 (c)). Third maxilliped generally glabrous; ischium subrectangular, longer than broad, with deep, broad, longitudinal medial sulcus; exopod long, exceeding upper edge of merus, straight, with well-developed flagellum, longer than merus width ( Figure 3 (a)). Chelipeds unequal, major (left) chela distinctly larger ( Figure 2 (a–d)). Ambulatory legs relatively slender, shorter than chelae, glabrous, generally smooth ( Figure 2 (a,b)). Pleon T-shaped, with strongly concave lateral margins ( Figure 2 (b,e)). G1 distally strongly bent outwards; distal half cylindrical, abruptly narrow, strongly bent; tip acute, gently hooked, directed obliquely outwards ( Figure 2 (b,c,e,f). G2 distal segment very short, slender, tapering ( Figure 2 (d)).

Description of holotype

Carapace subhexagonal, broader than long (cw/cl = ca. 1.3), relatively high (ch/cl = ca. 0.6); dorsal surface strongly inflated, glabrous, with numerous punctation; regions indistinct; cervical grooves narrow and shallow, not reaching level of postorbital cristae; H-shaped grooves distinct; branchial regions smooth, inflated; metabranchial region laterally with distinct oblique striae ( Figure 2 (a)). Anterolateral margins convex, with three prominent epibranchial teeth, tip of each tooth acute; epibranchial teeth stocky, progressively smaller, each tooth with broad base and acute tip; first and second teeth directed anteriorly; third epibranchial tooth directed anterolaterally ( Figure 2 (a)). Epigastric cristae well developed, sharp, smooth, distinctly anterior to postorbital cristae, separated from latter by shallow groove and from each other by distinct, long, posteriorly bifurcated mesogastric groove; postorbital cristae developed, rugose, straight, sloping posteriorly, not reaching margin ( Figure 2 (a)). External orbital angle broadly triangular, outer margin gently convex, ca. 2× length of inner margin, separated from first epibranchial tooth by triangular cleft ( Figure 2 (a)). Frontal region gently convex, smooth; frontal margin almost straight, cristate (fw/cw = ca. 0.3) ( Figure 2 (a)). Supraorbital and infraorbital margins sinuous, subcristate; orbital region relatively broad, with dense setae ( Figure 2 (c)). Suborbital and pterygostomial regions partly with strong granules ( Figure 2 (c)). Epistome anterior margin with low median triangle, posterior margin with well-developed, triangular median lobe, posterolateral margins sloping downward with gentle arch ( Figure 2 (c)). Eyes relatively small compared to orbital space; eye stalk short, stout, medially strongly concave; cornea moderately large, pigmented ( Figure 2 (c)). Antennular fossae rectangular in frontal view ( Figure 2 (c)).

Third maxilliped generally glabrous; ischium subrectangular, longer than broad (length ca. 1.7× width), proximal part distinctly tapered, with deep, broad, longitudinal medial sulcus; merus subovate, broader than long (length ca. 0.7× width), subequal to half of ischium length, with concave outer surface and smooth margins; exopod long, reaching up to half length of merus, straight, tapering distally, inner margin distally produced as tooth, with well-developed flagellum, longer than merus width ( Figure 3 (a)).

Chelipeds unequal, major (left) chela distinctly larger; outer surfaces of merus, carpus and palm generally smooth ( Figure 2 (a–d)). Major chela with four or five large, rounded teeth, remaining teeth smaller, small gape when fingertips in contact; fingers gently curved, subequal to palm length, with hooked, overlapping tips; palm longer than high, with gently inflated, smooth inner and outer surfaces; carpus with narrow, obliquely directed, sharp subdistal spine on inner margin; merus with subterminal spine ( Figure 2 (a,d)).

Ambulatory legs relatively slender, shorter than chelae, glabrous, generally smooth; merus with subterminal spine, anterior margin rugose; dactylus gently recurved, elongated, ca. 5.1× longer than proximal width, relatively longer than propodus, ca. 1.2× as long as propodus in fourth ambulatory leg ( Figure 2 (a,b)).

Suture between thoracic sternites 1 and 2 completely fused ( Figure 2 (b)); suture between thoracic sternites 2 and 3 sinuous, deep, broad, reaching lateral margins ( Figure 2 (b)); suture between thoracic sternites 3 and 4 shallow and narrow ( Figure 2 (b, e)); thoracic sternites 4 and 5 medially uninterrupted ( Figure 2 (g)); thoracic sternites 6 and 7 medially interrupted by longitudinal groove, with transverse ridge at suture separating the two sternites ( Figure 2 (g)). Sterno-pleonal cavity reaching beyond imaginary line joining anterior edge of cheliped coxae ( Figure 2 (b,g)).

Pleon T-shaped, with strongly concave lateral margins; pleonal somites 1, 2 shorter than somite 3; pleonal somites 3–5 trapezoidal, lateral margins convex in somites 3, 5 and gently concave in somite 4, proximal margin sinuous in somites 4 and 5; pleonal somite 6 distally broad and proximally narrow, distal margin ca. 1.2 × wider than proximal margin, proximal margin almost straight, lateral margins strongly concave ( Figure 2 (b,e)). Telson tongue shaped, subequal in length to pleonal somite 6, proximal margin sinuous, lateral margins concave, apex rounded ( Figure 2 (b,e)).

G1 distally strongly bent outwards; terminal and subterminal segments not separable; distal half cylindrical, abruptly narrow, strongly bent, appearing sinuous, with tip acute, gently hooked, directed obliquely outwards; proximal half stocky, strongly expanded, appearing suborbicular, outer margin with distinct, broad shelf, inner margin convex, lacking shelf ( Figure 2 (b,c,e,f). G2 distal segment very short, slender, tapering; basal segment with expanded outer margin ( Figure 2 (d)).

Paratypes

Female pleon is subovate, and covers entire thoracic sternites when closed ( Figure 2 (f)). Pleonal somites distinctly broader than long, with convex lateral margins; pleonal somite 1 is the shortest; pleonal somites 1–3 are progressively longer; pleonal somites 4 and 5 are almost equal in length; pleonal somite 6 is the longest ( Figure 2 (f)). Female telson is broadly triangular, much broader than long, with gently convex lateral margins ( Figure 2 (d,f)).

Female vulvae located on the thoracic sternite 6 are orbicular in shape, and each vulva occupies ca. 0.4× the length of the thoracic sternite 6, close to the suture between the thoracic sternite 5 and 6 ( Figure 2 (h)).

The male specimens on hand show no substantial variation in the key characters of the species discussed above.

Etymology

Esanthelphusa kayinensis sp. nov. is named after the type locality.

Colour in life

Crabs are dark purplish brown on dorsal surface and relatively paler on ventral surface, with pale yellow thoracic sternites ( Figures 2 (a–c, e–h, 4(a, b))).

Ecological notes

Esanthelphusa kayinensis sp. nov. was found to dwell inside shallow muddy burrows (up to 50 cm depth) along stream margins adjacent to rice fields and wetlands ( Figure 4 (c)).

Remarks

The new species most resembles E. dugasti and E. nimoafi in many features of the carapace and G1. Esanthelphusa kayinensis sp. nov. is nevertheless distinguished from them by the following diagnostic characters: (i) the distal half of the G1 strongly bent but appears sinuous ( Figure 3 (b,c,e,f)) (G1 distal half medially strongly bent at right angle from the longitudinal axis in E. dugasti and E. nimoafi ; cf. Yeo 2004, figs. 2B, C, 5C, D, I–K); (ii) the G1 tip is acute, gently hooked and directed obliquely outwards ( Figure 3 (b,c,e,f)) [vs the G1 tip broadly tapered, relatively less strongly hooked and directed downwards to obliquely outwards in E. dugasti (cf. Yeo 2004, fig. 2B–E); vs the G1 tip acute, relatively more strongly hooked and directed downwards to obliquely inwards in E.nimoafi (cf. Yeo 2004, fig. 5C–F,I– K)]. The new species, E. kayinensis sp. nov., also differs from E. dugasti and E. nimoafi by the third maxilliped, which has a proximally more strongly tapered ischium and a subovate merus (vs third maxilliped with a proximally less strongly tapered ischium and a subrectangular merus in E. nimoafi and E. dugasti ; cf. Yeo 2004, figs 2A, 5B). Furthermore, E. kayinensis sp. nov. can be differentiated from E. nimoafi by the anterolaterally directed third epibranchial tooth ( Figure 2 (a)) (vs third epibranchial tooth anteriorly directed; cf. Yeo 2004, fig. 5A) and the broadly triangular external orbital angle ( Figure 2 (a)) (vs external orbital angle acutely triangular; cf. Yeo 2004, fig. 5A).

Among the other known species of Esanthelphusa , only E. chiangmai and E. phetchaburi resemble E. kayinensis sp. nov. in that both possess a distally hooked G1 ( Figure 3 (b,c,e,f); cf. Ng and Naiyanetr 1993, figs 66B, C, F, G, 67B–F). The tip of the G1 is gently hooked and directed obliquely outwards in E. kayinensis sp. nov. ( Figure 3 (b,c,e,f)), whereas the G1 tip is strongly hooked and directed obliquely inwards in E. chiangmai and E. phetchaburi (cf. Ng and Naiyanetr 1993, figs 66B, C, F, G, 67B–F). The relatively high and more acute epibranchial teeth separate E. kayinensis sp. nov. ( Figure 2 (a)) from E. chiangmai and E. phetchaburi , which have relatively low and less acute epibranchial teeth (cf. Ng and Naiyanetr 1993, figs 31, 32). In biogeographical distribution, E. kayinensis sp. nov. is the first record of the genus Esanthelphusa species from Myanmar. Esanthelphusa chiangmai , being found in northern Thailand, is geographically closest to this new species (compared to E. dugasti and E. nimoafi in northeastern Thailand and E. phetchaburi in southern Thailand).

Geographic distribution

The new species is only known from the type locality, Hpa-An Township, Kayin, Myanmar, Kayin State, Myanmar ( Figure 1 ).

Phylogenetic analyses

The phylogenetic tree based on 16S produced similar gene tree topologies and congruently revealed three well-supported monophyletic clades, identified here as clades A, B, or C ( Figure 5 ). The gecarcinucid species analysed here are mainly categorised into three clades [clade C + (clade A + clade B)]: clade A consists of species from Oceania (shown in blue in Figure 5 ) and the Southeast Asia islands (shown in yellow in Figure 5 ); clade B includes mainly those species occurring in China and the adjacent Indochina Peninsula (shown in orange in Figure 5 ); and clade C comprises species from the Indian Peninsula (shown in green in Figure 5 ). The phylogenetic tree indicates that E. kayinensis sp. nov. clusters together with E. dugasti as a sister species with strong support (Bayesian posterior probabilitie / bootstrap values, BPP/BS = 0.98/98).

The minimum K2P genetic distance between E. kayinensis sp. nov. and its congener E. dugasti is 2.59 ± 0.77% ( Table 2 ), which is larger than the average genetic distance among congeneric species of the sister genus, Somanniathelphusa Bott, 1968 , in clade B (1.44 ± 0.46%, range 0.21–2.16%), but lower than the average genetic distance among the phylogenetically close genus, Sayamia Naiyanetr, 1994 (2.93 ± 0.67%, range 1.29– 4.43%) ( Table 2 ).

Figures

Figure 1. Map of Myanmar showing sampling sites (black circle) of Esanthelphusa kayinensis sp. nov.

Figure 2. Esanthelphusa kayinensis sp. nov., holotype, male, 31.58 × 25.34 mm, NNU16C-PA1 (a–e, g); paratypes, female, 29.65 × 24.49 mm, NNU16C-PA2 (f, h). (a) overall dorsal view; (b) overall ventral view; (c) frontal view of cephalothorax; (d) external view of major (left) chela; (e,f) ventral view of thoracic sternum with pleon; (g) thoracic sternum showing sterno-pleonal cavity and G1 in situ; h, thoracic sternum showing vulvae. White scale bar = 1.0 cm.

Figure 3. Esanthelphusa kayinensis sp. nov., holotype, male, NNU16C-PA1. (a) left third maxilliped; (b) ventral view of left G1; (c) dorsal view of left G1; (d) left G2; (e): ventral view of distal half of G1; f, dorsal view of distal half of G1. White scale bar = 1.0 cm.

Figure 4. Esanthelphusa kayinensis sp. nov.: (a, b) colour in life; (c) habitat.

Figure 5. Bayesian inference (BI) tree for the Esanthelphusa species and other freshwater crabs based on 16S rDNA sequences. Values at the nodes represent posterior probabilities and bootstrap values (BPP/BS). Five clades are recognised: Oceania clade (blue), Southeast Asia islands clade (yellow), China and Indochina Peninsula clade (orange), and Indian Peninsula clade (green). The new species is marked in bold and new sequences from the present study are indicated with asterisks.