Esanthelphusa dugasti ( Rathbun, 1902 )

Yeo, Darren C. J., 2004, A New Species Of Esanthelphusa (Crustacea: Brachyura: Parathelphusidae) From Laos, And A Redescription Of Potamon (Parathelphusa) Dugasti Rathbun, 1902, Raffles Bulletin of Zoology 52 (1), pp. 219-226 : 219-222

Esanthelphusa dugasti ( Rathbun, 1902)

( Figs. 1 , 2 )

Potamon (Parathelphusa) dugasti Rathbun, 1902: 185 ; 1905: 242, Pl. 11 fig. 10, Fig. 58.

Somanniathelphusa sinensis dugasti – Bott, 1968: 409, Figs. 13, 14, 31 (part); 1970a: 339 (part); 1970b: 112, Pl. 21 fig. 45-47, Pl. 30 fig. 82 (part); Chuensri, 1973: 14, Fig. 2C (part); 1974a: 20, Fig. 2C (part); 1974b: 16 (part).

Somanniathelphusa dugasti – Naiyanetr, 1975: 23 (part); 1978b: 6 (part), Fig. 5 , 1978c: 27 (part); 1980a: 50 (part); 1980b: 25 (part); 1988: 4 (part), Pl. 2 fig. 3; 1992: 48 (part); Ng, 1988: 105 (part); Naiyanetr & Takeda, 1989: 115 (part); Ng & Naiyanetr, 1993: 46.

Esanthelphusa dugasti – Naiyanetr, 1994: 698, Fig. 3 ; 1998: 106; Yeo & Ng, 1999: 642.

Sayamia dugasti – Ng & Kosuge, 1995: 61.

Material examined. – Holotype, male (46.0 by 36.7 mm) ( MNHNB 5113 ), Lakhone, Laos, Siam, coll. Dugast, no date.

Others - 4 males (largest 49.9 by 39.6 mm) ( ZRC), 2 males (larger 53.9 by 41.7 mm) ( CUMZ), That Phanom District, Nakhon Phanom Province, northeastern Thailand, coll. P. Naiyanetr, 17 Apr.1984 ; 1 male (32.1 by 25.9 mm), 1 female ( ZRC), 4 males, 4 females ( CUMZ), Muang Nakhon Phanom District, Nakhon Phanom Province, northeastern Thailand, coll. Manu, 22 Sep.1974 .

Description. – Carapace slightly broader than long, relatively high; dorsal surface strongly inflated, glabrous; regions indistinct, cervical grooves poorly developed, H-shaped groove well developed ( Figs. 1A, B ). Epigastric cristae well developed, sharp, smooth, separated by distinct groove which opens up into inverted V-shape posteriorly, slightly anterior to postorbital cristae, separated from postorbital cristae by distinct groove; postorbital cristae well developed but short, not reaching beginning of cervical grooves, gently convex, sharp, smooth; regions behind epigastric and postorbital cristae smooth ( Figs. 1A, B ). Frontal margin sinuous, cristate, with distinct, complete frontal median triangle; frontal region hardly deflexed, smooth; antennular fossae subrectangular when viewed from front; supraorbital margin sinuous, cristate; infraorbital margin sinuous, cristate; orbital region relatively broad; eyes normal; sub-hepatic and sub-branchial regions sparsely rugose ( Fig. 1 ). External orbital angle well developed, acutely triangular, with outer margin longer than inner margin, convex, margins cristate, with deep, narrow, triangular cleft separating it from first epibranchial tooth; anterolateral margin gently convex, with three distinct epibranchial teeth, well developed, triangular, relatively narrow, flattened, confluent with posterolateral margin; posterolateral margin strongly converging posteriorly, entire, straight; branchial region smooth; metabranchial region with weak oblique striae ( Fig. 1A ). Epistome anterior margin with median triangle; posterior margin median tooth distinct, well developed, broadly triangular, with acute tip, outer parts not concave, sloping downwards, lateral parts gently convex; median endostomial ridge absent ( Fig. 1B ).

Third maxilliped glabrous; ischium broadly rectangular, with distinct longitudinal median sulcus; merus squarish, subequal to half of ischium length, with concave outer surface, with smooth margins; palp normal; exopod long, exceeding upper edge of ischium, straight, distally tapered, inner margin of distal part produced as a tooth, with well developed flagellum, longer than merus width ( Fig. 2A ).

Chelipeds unequal (see Rathbun, 1905: Pl. 11 fig. 10), outer surface of merus, carpus and palm smooth; fingers gaping, longer than palm, tips hooked and overlapping, carpus with robust, obliquely directed subdistal spine on inner margin; merus with subterminal spine ( Fig. 1A ).

Ambulatory legs glabrous, relatively short, relatively slender; dactyli short, stout, merus subdistal spine present, upper margin smooth; fourth ambulatory leg dactylus about 1.3 times as long as propodus, about 5.2 times longer than proximal width; propodus, carpus and merus smooth ( Fig. 1A ).

Suture between anterior thoracic sternites 2 and 3 incomplete, gently sinuous; groove or suture between anterior thoracic sternites 3 and 4 not discernible; posterior thoracic sternite 5 medially interrupted; thoracic sternite 6 and 7 separated by longitudinal median line, with transverse ridge at suture separating the two sternites; abdominal cavity reaching imaginary line joining anterior edge of cheliped bases ( Fig. 1C ). Male abdomen T-shaped; telson tongue shaped, subequal to sixth segment, lateral margins concave, tip rounded, proximal margin sinuous; segment 6 distal margin distinctly longer than proximal margin, with distinctly concave lateral margins, proximal margin almost straight; segments 3 to 5 trapezoidal, with lateral margins of segment 5 and 3 slightly convex, lateral margins of segment 4 slightly concave ( Fig. 1C ).

G1 strongly bent outwards, stocky; terminal segment not separated from subterminal segment, distal part distinctly narrowed, appears shorter than proximal part, cylindrical, strongly curved outwards, almost perpendicularly, with bend or curve in median part, tip broadly tapered, hooked, directed downwards, groove for G2 ventral; proximal part expanded, with distinct, broad shelf on outer margin, with distinctly convex inner margin ( Figs. 2 B-E). G2 distal segment distinctly shorter than half of basal segment, slender, tapering; basal segment outer margin expanded ( Fig. 2F ).

Remarks. – Rathbun (1902) described Esanthelphusa dugasti [as Potamon (Parathelphusa) dugasti ] based on an unspecified number of specimens from “Lakhone, Laos, Siam ”, but gave the measurements of a male specimen as 46.5 by 36.8 mm. Rathbun (1905) subsequently listed a single male specimen from that locality, together with numerous specimens from other parts of Laos, as well as “Cochinchine”, in her material for E. dugasti ; however, only the male specimen from “Lakhone, Laos, Siam ” was designated as a type. The measurement of this single type specimen, which is therefore the holotype of E. dugasti , matches that originally given by Rathbun (1902). “Lakhone, Laos, Siam ” refers to the present day Nakhon Phanom Province of northeastern Thailand, and E. dugasti appears to be restricted to that area. Specimens collected from there closely match the holotype of E. dugasti and are clearly referable to the species (Yeo & Nguyen, 1999; P. Naiyanetr, pers. comm.; present study). Specimens from other areas previously referred to E. dugasti by Rathbun (1905), Bott (1968, 1970b), Dang (1975, 1980), and Naiyanetr (1975, 1978a, b, c, 1980a, 1988), actually represent different species, such as E. phetchaburi (Ng & Naiyanetr, 1993) , E. chiangmai (Ng & Naiyanetr, 1993) , Somanniathelphusa pax Ng & Kosuge, 1995 , and possibly some undescribed species including E. nimoafi , new species (see later; unpublished data; see also Ng & Naiyanetr, 1993; Yeo & Nguyen, 1999). The other new species will be described in a separate study, but it is important to note here that they clearly belong to Esanthelphusa and will not affect the current generic system.

Esanthelphusa dugasti most closely resembles E. nimoafi , E. phetchaburi and E. chiangmai in terms of the G1 structure, but can be externally distinguished from the latter two species by its more strongly developed, distinct postorbital cristae (versus postorbital cristae very low and weak, sometimes indistinct); longer anterolateral margins (versus shorter), with well developed and acute epibranchial teeth (versus epibranchial teeth relatively lower and broader); and much more strongly constricted sixth male abdominal segment, with very slender proximal part and strongly concave lateral margins (versus sixth male abdominal segment less strongly constricted, with relatively broader proximal part and less strongly concave lateral margins) ( Fig. 1 ; Ng & Naiyanetr, 1993: Figs. 31, 32). The G1 of E. dugasti differs from that of E. phetchaburi and E. chiangmai by the tip being broader and less strongly hooked (versus G1 tip sharper and more strongly hooked), and bent portion of the distal part being proportionately longer (versus proportionately shorter) ( Figs. 2 B-E; Ng & Naiyanetr, 1993: Figs. 66B, C, E-G, 67B-F). The differences between E. dugasti and E. nimoafi are covered in the Remarks for the latter (see later).

Distribution. – Nakhon Phanom Province, northeastern Thailand.

Figures

Fig. 1. Esanthelphusa dugasti (Rathbun, 1902), holotype male (46.0 by 36.7 mm) (MNHN-B 5113). A, dorsal view; B, frontal view; C. ventral view.

Fig. 2. Esanthelphusa dugasti (Rathbun, 1902), holotype male (46.0 by 36.7 mm) (MNHN-B 5113). A, left third maxilliped; B-E, right G1, B: dorsal view, C: ventral view, D: dorsal view of distal part, E: ventral view of distal part; F, right G2. Scales = 2.0 mm in A; 1.0 mm in B, C, F; 0.5 mm in D, E.

Fig. 5. Esanthelphusa nimoafi, new species. A-H, holotype male (34.6 by 27.2 mm) (ZRC 2003.0268); I, paratype male (30.1 by 23.9 mm) (ZRC 2003.0269); J, K, paratype male (32.5 by 23.9 mm) (ZRC 32.5 by 23.9 mm). A, anterior carapace; B, left third maxilliped; C-F, I- K, right G1, C, I, J: dorsal view, D, K: ventral view, E: dorsal view of distal part, F, ventral view of distal part; G, abdominal segments 5-7; H, right G2. Scales = 5.0 mm in A, B, G; 1.0 mm in C, D, H-K; 0.5 mm in E, F.

Fig. 3. Esanthelphusa nimoafi, new species, holotype male (34.6 by 27.2 mm) (ZRC 2003.0268). Dorsal view.