Viridotheres buergeri ( Rathbun, 1909 )

Ahyong, Shane T. & Ng, Peter K. L., 2021, The pinnotherid crabs from the Gulf of Siam described by Rathbun (1909) (Decapoda: Brachyura): revisited and revised, Raffles Bulletin of Zoology 69, pp. 188-211 : 189-191

Viridotheres buergeri ( Rathbun, 1909)

( Figs. 1–3 )

Pinnotheres bürgeri Rathbun, 1909: 109 . — Rathbun, 1910: 331, fig. 12. — Tesch, 1918: 248, 253.

Pinnotheres kutensis Rathbun, 1909: 110 . — Rathbun, 1910: 335, 336, fig. 19. — Tesch, 1918: 249, 252. — Suvatti, 1938: 69. — Suvatti, 1950: 159. — Silas & Alagarswami, 1967: 1200, 1223. — Schmitt et al., 1973: 50. — Naiyanetr, 1998: 104. — Naiyanetr, 2007: 118. [New synonymy]

Pinnotheres siamensis Rathbun, 1909: 111 . — Rathbun, 1910: 336, fig. 20. — Tesch, 1918: 249, 257, 258. — Suvatti, 1938: 70. — Suvatti, 1950: 160. — Silas & Alagarswami, 1967: 1209, 1223. — Schmitt et al., 1973: 86. — Naiyanetr, 1998: 105. — Naiyanetr, 2007: 118. [New synonymy]

Pinnotheres burgeri . — Suvatti, 1938: 69. — Suvatti, 1950: 159. — Silas & Alagarswami, 1967: 1197, 1223. — Naiyanetr, 1980: 42. — Naiyanetr, 1998: 104. — Naiyanetr, 2007: 118. — Ahyong, 2019: 108.

Pinnotheres buergeri . — Schmitt et al., 1973: 41.

Viridotheres burgeri . — Ahyong & Ng, 2007b: 221, 222. — Ahyong et al., 2012: 36, 43, 46. — Ahyong, 2020a: 429.

Viridotheres buergeri . — Ng et al., 2008: 251. — Ng & Ho, 2016b: 741. — Ahyong, 2020b: 429.

Type material. Holotype: ZMUC CRU-5929 , juvenile female (cl 2.1 mm, cw 2.1 mm), Koh Kram, 30 fm (= 55 m), coll. Th. Mortensen, 2 or 21 March 1900.

Other material examined. ZMUC CRU-9397 , male (cl 1.2 mm, cw 1.2 mm), south of Koh Kut , 17–20 fm (= 31–37 m), coll. Th. Mortensen, 28 January 1900 (holotype of Pinnotheres kutensis Rathbun, 1909 ) ; ZMUC CRU-8111 , juvenile female (cl 1.3 mm, cw 1.3 mm), south of Koh Kut , 17–20 fm (= 31–37 m), mud, coll. Th. Mortensen, 28 January 1900 (holotype of Pinnotheres siamensis Rathbun, 1909 ) .

Description (based on female holotype of P. buergeri and male holotype of P. kutensis ). Carapace subcircular, as long as wide, widest at midlength, weakly arched axially or transversely; pterygostomial surface glabrous or sparsely setose. Front produced, anterior margin weakly concave in dorsal view (female), weakly convex (male); width about 0.3× cw. Dorsum smooth, glabrous. Epistome interantennular septum triangular; median buccal margin with narrow, triangular median point. Antennular sinus of similar size to orbit; antennules folded obliquely. Antennal articles 1 and 2 fused to epistome. Eyes visible in dorsal view, filling orbit, cornea pigmented.

Mxp3 ischiomerus length about twice width; outer margin convex; inner concave, distal margin rounded, with distinct angle. Carpus and propodus length subequal. Propodus tapering in distal half, apex rounded, dorsally and distally setose, length less than twice dactylus length. Dactylus digitiform, distally setose, inserted near propodal midlength, apex slightly overreaching propodus. Exopod inner margin gently convex, outer margin strongly convex; flagellum with 2 articles, distally setose.

Chelipeds symmetrical from left to right, glabrous except for inner ventral margin and occlusal margins of dactylus and pollex. Dactylus and pollex relatively straight, crossing distally, with slight gape, apices simple, neither expanded distomesially. Dactylus occlusal margin gently concave to straight, with blunt triangular tooth proximal to midlength, with row of minute finely graded denticles; proximal margin setose, most prominent on proximal half, extending onto dorsal margin palm. Pollex occlusal margin with convex proximal lobe, straight, sparsely setose, distal margin with row of slender finely graded denticles; with fringe of setae on inner ventral margin. Propodus palm dorsal margin 1.1× height (male), 1.3 (female), 0.9× length of dactylus (male), 1.1 (female); ventral margin gently sinuous. Carpus unarmed, glabrous.

P2–5 subequal from left to right, unarmed, almost glabrous in females, with natatory setae in males. Relative lengths: P3> P4> P2> P5. P2 basis anterior surface smooth. Dactyli similar, simple, falcate, apex sharp, glabrous or sparely setose, flexor margin unarmed; P2–4 dactyli 0.4× propodus length, of P5, 0.5× propodus length. Relative dactylus lengths: P3> P2 = P4> P5.

Thoracic sternum anterior margin medially emarginate; sternites 1–3 indistinguishably fused, setose.

Pleon narrow, triangular, of 6 free somites and telson; widest at somite 3; telson semi-circular, wider than anterior margin of somite 6 (male), as wide as anterior margin of somite 6 (subadult females). G1 arcuate, apex simple, with short distal point; G2 about ⅓ G1 length, exopod slightly shorter than endopod.

Remarks. On the basis of present study of the type material of Pinnotheres buergeri ( Fig. 1 ), P. kutensis ( Fig. 2 ), and P. siamensis ( Fig. 3 ), we consider that their respective holotypes each represent different sexes or different developmental phases of the same species. The holotype of P. buergeri is a juvenile female in which the pleopods are present only as buds and the pleon is of the narrow male-like form. The holotype of P. siamensis is also a juvenile female, but much smaller than that of P. buergeri , and appears to be a relatively recent post-moult specimen given the soft, slightly distorted pleon and carapace. The holotype of P. kutensis appears to be a near mature male, based on the well-developed gonopods. The three nominal species are linked by similar Mxp3 and P2–5 dactylus morphology, notably in the similar maxillipedal ischiomerus form and propodus shape, features comparable between both sexes where known (e.g., V. takedai Ahyong, Komai & Watanabe, 2012 : figs. 1B, 2B). Also, the P2–5 dactylus differences between specimens follow expected early through late juvenile changes in increasing stoutness with increasing body size. Evidently, Rathbun (1909, 1910) did not consider sexual dimorphism and allometry in naming these as separate species, despite the respective holotypes of P. kutensis and P. siamensis , and a non-type specimen of P. buergeri (see Rathbun, 1910: 331), all being collected together from the same station. It remains possible that P. buergeri , P. kutensis , and P. siamensis are separate species, but on the basis of their morphological and geographical continuity, we conclude that all three are conspecific and they are herein synonymised. Given that they were described simultaneously in the same paper, we select P. buergeri to have nomenclatural priority over P. kutensis and P. siamensis whenever the three names are treated as synonyms.

Ahyong & Ng (2007b) referred P. buergeri to Viridotheres based on the account of Rathbun (1909, 1910), and suggested that it is most similar to V. otto Ahyong & Ng, 2007 , from the Philippines. The present re-examination of V. buergeri corroborates Ahyong & Ng’s (2007b) comparisons between V. buergeri and V. otto , but also identifies a further distinguishing feature: the inner distal angle of the Mxp3 ischiomerus is obtusely angled in V. buergeri but broadly rounded in V. otto (see Ahyong & Ng, 2007b: fig. 26C). Although the generic placement of V. buergeri is fully consistent with the original diagnosis of the genus ( Manning, 1996), as observed by Ahyong et al. (2012), distinctions between Viridotheres and Nepinnotheres are subtle and will require re-evaluation.

Distribution. Presently known only from the Gulf of Thailand.

Figures

Fig. 1. Viridotheres buergeri (Rathbun, 1909), juvenile female holotype of Pinnotheres buergeri Rathbun, 1909, cl 2.1 mm, cw 2.1 mm, Koh Kram, Thailand, ZMUC CRU-5929. A, dorsal habitus; B, pleon; C, right maxilliped 3; D, anterior cephalothorax; E, anterior thoracic sternum; F, right chela; G–J, left P2–5, respectively; K–N, right P2–5, respectively. Scale: A, B = 1.0 mm; C = 0.25 mm; D–N = 0.5 mm.

Fig. 2. Viridotheres buergeri (Rathbun, 1909), juvenile male holotype of Pinnotheres kutensis Rathbun, 1909, cl 1.2 mm, cw 1.2 mm, south of Koh Kut, Thailand, ZMUC CRU-9397. A, dorsal habitus; B, lower buccal margin; C, anterior thoracic sternum; D, right maxilliped 3; E, right chela; F–I, right P2–5, respectively; J, pleon; K, right G1, sternal view; L, right G1, pleonal view; M, right G1, pleonal view. Scale: A = 0.5 mm; B–M = 0.25 mm.

Fig. 3. Viridotheres buergeri (Rathbun, 1909), juvenile female holotype of Pinnotheres siamensis Rathbun, 1909, cl 1.3 mm, cw 1.3 mm, south of Koh Kut, Thailand, ZMUC CRU-8111. A, dorsal habitus; B, lower buccal margin; C, anterior thoracic sternum; D, pleon; E, right chela; F–I, right P2–5, respectively. Scale: A = 0.5 mm; B–I = 0.25 mm.