The pinnotherid crabs from the Gulf of Siam described by

188

Ahyong & Ng: Gulf of Siam Pinnotheridae

The pinnotherid crabs from the Gulf of Siam described by Rathbun (1909) (Decapoda: Brachyura): revisited and revised

Shane T. Ahyong1 & Peter K. L. Ng2

Abstract. Increasing attention to the systematics of Southeast Asian pinnotherid crabs has required the re-evaluation of many species described in older works in order to correctly recognise and characterise new species. The pinnotherids from Thailand are known on the basis of only four studies, the most important being that by Mary Rathbun in 1909, who described seven new species from the Gulf of Thailand: Pinnotheres buergeri, P. kamensis, P. kutensis, P. lanensis, P. nigrans, P. quadratus, and P. siamensis. The seven species are reviewed and figured based on type material. Pinnotheres buergeri, currently assigned to Viridotheres, is a senior synonym of P. kutensis and P. siamensis, both of which are earlier juvenile stages of the same species. Pinnotheres kamensis,also based on a juvenile holotype, is a junior synonym of Arcotheres similis (Bürger, 1895). Pinnotheres lanensisand P. quadratus are each valid species of Arcotheres, and mature at a much smaller size than known congeners.Pinnotheres nigrans is a junior synonym of A. purpureus Alcock, 1900. The re-assessment of P. nigrans requireda study of A. purpureus and its close congener, A. boninensis (Stimpson, 1858), both of which are redescribed,the latter based on a newly designated neotype.

Key words. Pea crab, Crustacea, Brachyura, Pinnotheridae, Southeast Asia, Thailand

RAFFLES BULLETIN OF ZOOLOGY 69: 188–211Date of publication: 21 June 2021DOI: 10.26107/RBZ-2021-0016 http://zoobank.org/urn:lsid:zoobank.org:pub:563ADA2B-90D3-465C-9E2A-6595189F447E

© National University of SingaporeISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)

INTRODUCTION

The last two decades have seen increasing attention on the systematics of the pinnotherine pinnotherid crabs of Southeast Asia, with recognition of numerous new species and genera (e.g., Manning, 1998; Campos, 2001; Ng & Manning, 2003; Ahyong & Ng, 2005, 2007a, b, 2008, 2020; Ng & Ngo, 2010; Ng, 2014; Ng & Ho, 2016a; Ng, 2018a, b; Ahyong, 2019; Ng et al., 2019a, b; Komai et al., 2020; Ng & Ahyong, in preparation). Taxonomic progress on the Southeast Asian and wider Indo-West Pacific fauna has been substantially facilitated by Ahyong & Ng’s (2007b) redescription of the type material of the species described by Bürger (1895), the foundational work on Pinnotheridae for the region.

Pinnotherines from Thailand are known on the basis of only four studies (excluding checklists): Rathbun (1909, 1910), Campos (2001) and Ng & Ho (2016b), together recording a total of 14 species. The most important of these studies,

published by Mary Rathbun in 1909, described seven new species of pinnotherines from the Gulf of Thailand; she later (Rathbun, 1910) included partial illustrations of these species and reported additional pinnotherine records from the Gulf of Thailand: Pinnotheres affinis Bürger, 1895, P. cardii Bürger, 1895, P. glaberrimus Bürger, 1895, P. gracilis Bürger, 1895, P. parvulus Stimpson, 1858.

All of the species described by Rathbun (1909) were based on comparatively small specimens, most being juveniles < 3 mm cl, and without host records, information that is extremely useful in assisting identification of the crabs (Ng & Kumar, 2015; Ng, 2018b). Rathbun’s (1910) record of P. cardii was referred to Amusiotheres obtusidentatus (Dai, Feng, Song & Chen, 1980) (Ng et al., 2019b) but other species reported by Rathbun (1909, 1910) cannot be reliably recognised based on her accounts owing to insufficient descriptions and illustrations, thus impeding advancement of the taxonomy of pinnotherids in the region. To facilitate further taxonomic progress on the Southeast Asian Pinnotheridae, we herein revise the species described by Rathbun (1909) and revise the identification of Pinnotheres parvulus Stimpson, 1858, reported by Rathbun (1910). In some cases, reassessment of Rathbun’s (1909) species has also required reconsideration of allied taxa, such as the inadequately known, Pinnotheres boninensis Stimpson, 1858, described from Japan. Therefore, we also take the opportunity to redescribe Pinnotheres boninensis Stimpson, 1858, based on a neotype designated in this study.

Taxonomy & Systematics

Accepted by: Jose Christopher E. Mendoza

1Australian Museum Research Institute, Australian Museum,1 William Street, Sydney NSW 2010, Australia, and School of Biological, Earth & Environmental Sciences, University of New South Wales, NSW 2052, Australia; Email: [email protected] Kong Chian Natural History Museum, Faculty of Science, National University of Singapore, 2 Conservatory Drive, Singapore 117377, Republic of Singapore; Email: [email protected]

189

RAFFLES BULLETIN OF ZOOLOGY 2021

MATERIAL AND METHODS

Morphological terminology follows Ahyong & Ng (2007b) and Ahyong et al. (2012). Specimen measurements are in millimetres (mm). Carapace length (cl) is measured along the dorsal midline. Carapace width (cw) is the greatest width. Maxilliped 3 is abbreviated Mxp3 and the male gonopods 1 and 2 are abbreviated G1 and G2, respectively. Pereopods 2–5 (ambulatory legs 1–4) are abbreviated P2–5, respectively. Specimens studied are deposited in the following institutions: Australian Museum, Sydney (AM); The Natural History Museum, London (NHM); Lee Kong Chian Natural History Museum, National University of Singapore (ZRC); Natural History Museum of Denmark (Zoological Museum), University of Copenhagen (ZMUC); and National Museum of Nature and Science, Tokyo (NSMT).

SYSTEMATICS

Family Pinnotheridae De Haan, 1833

Subfamily Pinnotherinae De Haan, 1833

Viridotheres Manning, 1996

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

190


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.

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.

191


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.

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.

192


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.

Arcotheres Manning, 1993

Arcotheres lanensis (Rathbun, 1909), new combination(Figs. 4, 5)

Pinnotheres lanensis Rathbun, 1909: 109. — Rathbun, 1910: 332, fig. 14. — Tesch, 1918: 249, 255. — Gordon, 1936: 179. — Suvatti, 1938: 69. — Suvatti, 1950: 159. — Silas & Alagarswami, 1967: 1201, 1223. — Schmitt et al., 1973: 86. — Naiyanetr, 1980: 42. — Naiyanetr, 1998: 104. — Naiyanetr, 2007: 118. — Ng et al., 2008: 250.

Type material. Holotype: ZMUC CRU-7022, ovigerous female (cl 2.3 mm, cw 2.6 mm), Koh Lan, 30 fm (= 55 m), mud, coll. Th. Mortensen, 2 March 1900.

Description of holotype. Carapace slightly wider than long, soft, in poor condition, irregularly subcircular; front not produced, anterior margin convex in dorsal view; anterolateral margins poorly defined; dorsum smooth, glabrous; dorsal surface convex in profile. Epistome with narrow interantennular septum; median buccal margin with low, obtuse median point. Antennular sinus of similar size to

193


Fig. 4. Arcotheres lanensis (Rathbun, 1909), ovigerous female holotype, cl 2.3 mm, cw 2.6 mm, Koh Lan, Thailand, ZMUC CRU-7022. A, overall habitus; B, ventral view of cephalothorax.

orbit; antennules folded slightly obliquely. Antennal articles 1 and 2 fused to epistome. Eyes not visible in dorsal view, filling orbit, cornea pigmented.

Mxp3 ischiomerus length about 1.6× width; outer margin strongly convex; inner proximal margin convex; inner distal margin obtusely rounded. Carpus shorter than propodus. Propodus spatulate, apex rounded, dorsally and distally setose. Dactylus digitiform, distally setose, inserted slightly proximal to propodal midlength, apex not reaching end of

propodus. Exopod inner margin almost straight, outer margin convex; flagellum with 2 articles, distally setose.

Chelipeds symmetrical from left to right, surfaces glabrous except inner, lower distal margin. Dactylus and pollex relatively straight, crossing distally, without gape; apices simple, not expanded mesially. Dactylus occlusal margin with blunt triangular tooth proximal to midlength, margin straight in distal half, finely denticulate, sparsely setose. Pollex occlusal margin irregularly convex proximally, almost

194


Fig. 5. Arcotheres lanensis (Rathbun, 1909), ovigerous female holotype, cl 2.3 mm, cw 2.6 mm, Koh Lan, Thailand, ZMUC CRU-7022. A, carapace; B, right maxilliped 3; C, lower buccal margin; D, anterior thoracic sternum; E, right chela; F–I, left P2–5, respectively; J, right P2; K–L, right P4, P5, respectively. Scale: A = 1.0 mm; B = 0.25 mm; C–L = 0.5 mm.

straight in distal half, finely denticulate, sparsely setose; with fringe of short setae on inner ventral margin. Propodus palm dorsal margin 1.5× height, 1.1× length of dactylus; palm ventral margin almost straight. Carpus unarmed.

P2–5 unarmed, largely glabrous, setae densest on P5 dactylus. P2, 3, and 5 similar, symmetrical from left to right; right P4 length 1.3× longer than left; relative lengths in decreasing order: P4 (longer) > P5 > P3 > P2. Longer P4 merus about 0.4× pcl. P2–3 dactylus subequal, 0.6× propodus length, longer than half length of P4 and 5 dactyli, evenly arcuate,

distally acute, flexor margin unarmed, glabrous. P4 dactylus slender, weakly curved, sparsely setose, unarmed; left dactylus as long as propodus; right dactylus 0.7× propodus length. P5 dactylus slightly longer than propodus, slender, weakly curved, subequal to P4 dactylus; extensor margin with few short setae, flexor margin lined with long setae, unarmed. Relative dactylus lengths: P4 (longer) ~ P5 > P3 > P2.

Thoracic sternum anterior margin weakly concave medially; sternites 1–3 indistinguishably fused.

195


Pleon of 6 free somites and telson, extending to buccal region, covering bases of P2–P5.

Remarks. Pinnotheres lanensis is referred to Arcotheres on the basis of the asymmetrical P4, the elongated and slender P4–5 dactyli that are longer than those of P2 and P3, and the perpendicular articulation between the ischium and merus of P5. Arcotheres lanensis is most similar to A. exiguus, which it resembles in most respects. The two species, however, differ in the proportional length of the P2 and P3 dactyli (distinctly exceeding half the length of the dactyli of P5 and the longer P4 in A. lanensis, distinctly shorter than half in A. exiguus), as well as the size at maturity. Arcotheres lanensis is already ovigerous by cl 2.3 mm, whereas A. exiguus is not mature until about twice that size (Ng & Ahyong, in preparation). In addition, even in A. exiguus of a similar size to the holotype of A. lanensis, the P5 dactylus is still distinctly more elongated, resembling that of the largest specimens of A. exiguus (Ng & Ahyong, in preparation). Arcotheres lanensis also resembles A. quadratus, A. similis, and A. latus (Bürger, 1895) in the presence of the elongated P2 and P3 dactyli that exceed half the length of the dactyli of P5 and the longer P4, but is readily separated by the unarmed flexor margin of the P5 dactylus (versus one or two rows of spinules on the distal half of the flexor margin in A. quadratus, A. similis, and A. latus). As with A. exiguus, A. similis and A. latus mature at at least least twice the size of A. lanensis, whereas A. quadratus is mature at a similarly small size (Ng & Ahyong, in preparation).

Distribution. Presently known only from the Gulf of Thailand.

Arcotheres quadratus (Rathbun, 1909), new combination(Figs. 6, 7)

Pinnotheres quadratus Rathbun, 1909: 110. — Rathbun, 1910: 333, fig. 15. — Tesch, 1918: 250, 255. — Suvatti, 1938: 70. — Suvatti, 1950: 160. — Silas & Alagarswami, 1967: 1207, 1208, 1223, 1225. — Schmitt et al., 1973: 6, 83. — Naiyanetr, 1980: 42. — Naiyanetr, 1998: 105. — Naiyanetr, 2007: 118. — Ng et al., 2008: 251.

Questionable records: Pinnotheres quadratus. — Tesch, 1918: 261, 288, 289, pl. 17 fig. 2. — Chhapgar, 1957a: 506, pl. 12l, m. — Chhapgar, 1957b: 44, pl. 12l, m. — Chhapgar, 1958: 254, fig. 2a, b.

Type material. Holotype: ZMUC CRU-7921, ovigerous female (cl 2.8 mm, cw 2.9 mm), Koh Chang, 1 fm (= 1.8 m), coral, January–March 1900.

Description of holotype. Carapace slightly wider than long, sub-oblong, front not produced, anterior margin weakly sinuous in dorsal view; anterolateral margins poorly defined; dorsum smooth, glabrous; dorsal surface convex in profile. Epistome with narrow interantennular septum; median buccal margin with low, obtuse median point. Antennular sinus of similar size to orbit; antennules folded slightly obliquely. Antennal articles 1 and 2 fused to epistome. Eyes partially visible in dorsal view, filling orbit, cornea pigmented.

Mxp3 ischiomerus length about twice width; outer margin strongly convex; inner proximal margin convex; inner distal margin obtusely, bluntly angular. Carpus shorter than propodus. Propodus spatulate, apex rounded, dorsally and distally setose. Dactylus digitiform, distally setose, inserted slightly proximal to propodal midlength, apex not reaching end of propodus. Exopod inner margin almost straight, outer sinuous; flagellum with 2 articles, distally setose.

Cheliped surfaces glabrous except inner, lower distal margin. Dactylus and pollex relatively straight, crossing distally, without gape; apices simple, not expanded mesially. Dactylus occlusal margin with blunt triangular tooth proximal to midlength, margin straight in distal half, finely denticulate, sparsely setose. Pollex occlusal margin with 2 rounded lobes proximally, weakly convex in distal half, finely denticulate, sparsely setose; with fringe of short setae on inner ventral margin. Propodus palm dorsal margin 1.7× height, 1.4× length of dactylus; palm ventral margin almost straight. Carpus unarmed.

P2–5 unarmed, largely glabrous, densest on P5 dactylus. P2, 3, and 5 similar, symmetrical from left to right; left P4 length 1.4× longer than right; relative lengths in decreasing order: P4 (longer) > P5 > P3 > P2. Longer P4 merus about 0.4× pcl. P2–3 dactylus subequal, 0.5× propodus length, half length of P4 (longer) and 5 dactyli, evenly arcuate, distally acute, flexor margin unarmed, glabrous or with few short setae. P4 dactylus slender, weakly curved, about 0.9× propodus length. P5 dactylus slightly longer than propodus, slender, weakly curved, slightly longer than P4 dactylus; extensor margin with few short setae, flexor margin lined with long setae, distal flexor margin with row of 4 spinules. Relative dactylus lengths: P5 > P4 (longer) > P3 = P2.

Thoracic sternum anterior margin weakly convex medially; sternites 1–3 indistinguishably fused.


Remarks. Like Pinnotheres lanensis, P. quadratus is referrable to Arcotheres on the basis of the asymmetrical P4, the elongated and slender P4 and P5 dactyli that are longer than those of P2 and P3, and the perpendicular articulation between the P5 ischium and merus. Arcotheres quadratus, A. similis, and A. latus share the presence of elongated P2 and P3 dactyli that exceed half the length of the dactyli of P5 and the longer P4, and the presence of spinules on the distal flexor margin of the P5 dactylus. A single row of P5 spinules is present in A. quadratus and two rows in A. similis and A. latus. Arcotheres quadratus also differs from A. similis and A. latus in carapace proportions (about as long as wide versus distinctly wider than long), and the size at maturity (ovigerous at less than 3 mm cl versus 4.7 mm and 7.6 mm in A. similis and A. latus, respectively; Ng & Ahyong, in preparation). The quadrate carapace of A. quadratus might prove to be taxonomically useful, but until more specimens become available to assess variability in the species, carapace shape should be used with caution given its variability in

196


Fig. 6. Arcotheres quadratus (Rathbun, 1909), ovigerous female holotype, cl 2.8 mm, cw 2.9 mm, Koh Chang, Thailand, ZMUC CRU-7921. A, overall habitus; B, frontal view of cephalothorax; C, ventral view of cephalothorax.

some congeners such as A. palaensis and A. exiguus (see Ng & Ahyong, in preparation). The minute size at maturity of female A. quadratus (and A. lanensis), with both being ovigerous at less than cl 3.0 mm, is conspicuous and, to our knowledge, unique in Arcotheres; they may represent dwarf species in the genus.

Records of A. quadratus from outside the type locality require confirmation. Tesch (1918) recorded a male and ovigerous female from Indonesia (Lombok and Waigeu Island, respectively), hosted by Arca sp., which can be referred to Arcotheres based on the elongated P4 and P5 dactyli that are “about twice as long” as the P2 and P3 dactyli. Unfortunately, Rathbun (1909) did not record the host of any of her pinnotherids, but Tesch’s (1918) brief account is not inconsistent with what we know of A. quadratus (although it

could equally apply to A. lanensis). Notably, Tesch’s (1918) ovigerous female from Waigeu Island, as in A. quadratus and A. lanensis, is minute (cl 2.9 mm, cw 3.2 mm) and might represent either of the two species. Tesch’s (1918: pl. 17 fig. 2) “male” from Lombok, however, is depicted with a comparatively wide, triangular pleon suggestive of a juvenile female rather than male. Given the immaturity at its size (cl 2.4 mm, cw 2.8 mm), the Lombok specimen is probably not A. quadratus, and might be referrable to other species of the genus known from there, such as A. palaensis (Bürger, 1895) or A. ocularius Komai, Kawai & Ng, 2020 (Komai et al., 2020). Chhapgar (1957a: pl. 12l, m) (repeated by Chhapgar, 1957b, 1958) figured a “male” of A. quadratus without locality in the context of a comparison with his new Indian species, Pinnotheres vicajii Chhapgar, 1957 (= Arcotheres exiguus (Bürger, 1895), see Trivedi et

197


Fig. 7. Arcotheres quadratus (Rathbun, 1909), ovigerous female holotype, cl 2.8 mm, cw 2.9 mm, Koh Chang, Thailand, ZMUC CRU-7921. A, dorsal habitus; B, right maxilliped 3; C, anterior carapace margin; D, anterior cephalothorax; E, anterior thoracic sternum; F, right chela; G–J, left P2–5, respectively; K–N, right P2–5, respectively. Scale: A = 2.0 mm; B = 0.5 mm; C–N = 1.0 mm.

al., 2020); it appears to be re-drawn based on Tesch (1918: pl. 17 fig. 2) and does not constitute an independent record.

Distribution. Presently known with certainty only from the Gulf of Thailand; possibly from Indonesia.

Arcotheres boninensis (Stimpson, 1858)(Figs. 8, 9)

Pinnotheres boninensis Stimpson, 1858: 108. — Miers, 1886: 276. — Stimpson, 1907: 141, 142. — Tesch, 1918: 248, 251, 286. — Sakai, 1936: 197, 198, pl. 56 fig. 1. — Sakai, 1939: 588, 589, pl. 69 fig. 1. — Sakai, 1956: 50. — Sakai, 1965:

177, pl. 87 fig. 1. — Silas & Alagarswami, 1967: 1196, 1225. — Suzuki, 1972: 14, text-fig. 11. — Schmitt et al., 1973: 6, 10, 40. — Sakai, 1976: 568, 571, pl. 200 fig. 3. — Dai et al., 1980: 135, fig. 6. — Takeda, 1982: 202, fig. 598. — Miyake, 1983: 155, pl. 52 fig. 1. — Dai et al., 1986: 394, fig. 210. — Takeda & Konishi, 1988: 137. — Dai & Yang, 1991: 426, fig. 210. — Takeda, 1993: 60. — Konishi, 1996: 15. — Ho & Hung, 1997: 37. — Muraoka, 1998: 48. — Ng et al., 2001: 48. — Marumura & Kosaka, 2003: 67. — Hewitt, 2004: tables 1, 2. — Ng et al., 2008: 250. — Yang et al., 2008: 808. — Konishi, 2010: 32, 38. — Komatsu, 2011: 277. — Ng, Shih et al., 2017: 129.

Pinnotheres purpureus. — Sakai, 1933: 978, 979, fig. 2a.Arcotheres boninensis. — Ahyong & Ng, 2020: 337.

198


Fig. 8. Arcotheres boninensis (Stimpson, 1858), spent female neotype, cl 6.0 mm, cw 8.8 mm, Ogasawara Islands, Japan, NSMT 6567a. A, overall habitus; B, ventral view of cephalothorax; C, frontal view of cephalothorax; D, outer view of left chela.

Type material. Neotype (here designated): NSMT Cr6567a, spent female (cl 6.0 mm, cw 8.8 mm), Ogasawara Islands, Japan.

Other material examined. JAPAN: NSMT Cr6567b, 4 ovigerous females (cl 5.5 mm, cw 7.6 mm to cl 5.7 mm, cw 8.5 mm), 9 spent females (cl 3.8 mm, cw 5.0 mm to cl 6.2 mm, cw 9.2 mm), Ogasawara Islands. NEW CALEDONIA: AM P64781, 3 females (cl 5.8 mm, cw 8.2 mm to cl 6.2 mm, cw 9.2 mm), Ouvea, New Caledonia, 20°33′S, 166°27′E, in oysters on reef, coll. W. Burrell.

Description of female. Carapace wider than long, transversely ovate, inflated; front weakly produced, anterior margin transverse in dorsal view; anterolateral margins poorly defined; dorsum smooth, glabrous; dorsal surface convex in profile. Epistome with narrow interantennular septum; median buccal margin with low, obtuse median point. Antennular sinus of similar size or slightly larger than orbit; antennules folded slightly obliquely. Antennal articles 1 and 2 fused to epistome. Eyes partially visible in dorsal view, filling orbit, cornea pigmented.

199


Fig. 9. Arcotheres boninensis (Stimpson, 1858), spent female neotype, cl 6.0 mm, cw 8.8 mm, Ogasawara Islands, Japan, NSMT Cr6567a. A, dorsal habitus; B, right maxilliped 3; C, anterior carapace margin; D, anterior cephalothorax; E, anterior thoracic sternum; F, right chela; G–J, left P2–5, respectively; K–N, right P2–5, respectively. Scale: A = 2.0 mm; B = 0.5 mm; C–N = 1.0 mm.

Mxp3 ischiomerus length about twice width; outer margin strongly convex; inner proximal margin weakly convex; inner distal margin with blunt, obtuse to almost right-angled. Carpus shorter than propodus. Propodus gently tapering in distal half, apex rounded, dorsally and distally setose. Dactylus digitiform, distally setose, inserted slightly distal to propodal midlength, apex reaching to or beyond end of

propodus. Exopod inner margin almost straight, outer margin sinuous; flagellum with 2 articles, distally setose.

Chelipeds symmetrical from left to right, surfaces glabrous except inner, lower distal margin. Dactylus and pollex relatively straight, crossing distally, without gape, apices simple, not expanded. Dactylus occlusal margin with blunt

200


triangular tooth proximal to midlength, straight margin in distal half, finely denticulate, sparsely setose. Pollex occlusal margin with two, low, irregular teeth proximal to midlength, margin straight in distal half, finely denticulate, sparsely setose; with fringe of short setae on inner ventral margin. Propodus palm dorsal margin 1.3–1.6× height, 1.1–1.4× length of dactylus; ventral margin almost straight. Carpus unarmed.

P2–5 unarmed, almost glabrous except for dactyli, densest on P5 dactylus. P2, 3, and 5 similar, symmetrical from left to right; right P4 length 1.2–1.3× longer than left; relative lengths in decreasing order: P4 (longer) > P5 > P3 > P2. Longer P4 merus about 0.5× pcl. P2–3 dactylus about 0.5× propodus length, evenly arcuate, distally spiniform, flexor margin minutely denticulate; P3 dactylus slightly longer than P2. Longer P4 dactylus slender, weakly curved, unarmed, 0.8–1.0× propodus length; shorter P4 dactylus, 0.6× propodus length, flexor margin minutely denticulate. P5 dactylus as long as propodus, slender, weakly curved, 0.8–0.9× P4 dactylus length; surfaces covered in upright setae, slightly longer on flexor margin; flexor distal margin with two rows of spines, otherwise unarmed. Relative dactylus lengths: P4 (longer) > P5 > P3 > P2.

Thoracic sternum anterior margin shallowly concave medially; sternites 1–3 indistinguishably fused.


Remarks. Arcotheres boninensis (Stimpson, 1858), together with A. pernicola (Bürger, 1895), A. pollus Ahyong & Ng, 2020, and A. purpureus (Alcock, 1900) appear to form a discrete group in the genus—here called the A. boninensis group—united by the strongly arched, transversely elliptical carapace, and long, slender, almost styliform dactyli of P4 and 5 that are about twice the length of those of P2 and 3 (Ahyong & Ng, 2020). In addition, when the colouration has been recorded (not known for A. pollus), the species of the group are generally purplish-black in life, and, except for A. pollus, are hosted by ostreid oysters (Fig. 10; Alcock, 1900; Rathbun, 1909; Sakai, 1976; Trivedi et al., 2019). Distinctions between A. pernicola, A. boninensis, and A. purpureus, however, are not currently clear, partly due to the very poor condition of the type material of A. pernicola, and problems and ambiguities in diagnoses of the latter two species.

Arcotheres boninensis was described from the Bonin Islands (= Ogasawara Islands), Japan, and has since been reported from Taiwan, Hainan Island and northwestern Australia (Hewitt, 2004; Yang et al., 2008). Material of A. boninensis from New Caledonia is included herein to document its presence there, making it the sixth species of pinnotherid to be recorded from New Caledonia (Ng & Richer de Forges, 2007; Ahyong, 2020a). The taxonomy of A. boninensis, however, is problematical; the true identity of Stimpson’s (1858) species cannot be clearly determined because the original description is minimal and the type material lost

(Schmitt et al., 1973). Therefore, to progress taxonomic resolution in the A. boninensis group, we select a neotype for A. boninensis to fix the identity of the species. The neotype is an adult female (cl 6.0 mm, cw 8.8 mm, NSMT Cr6567a) from the Ogasawara Islands, Japan, corresponding to the form usually referred to Stimpson’s (1858) species. Variation within the present series of A. boninensis is slight, with the Mxp3 dactylus usually reaching beyond the end of the propodus (occasionally reaching only to the end). The length of the P5 dactylus varies allometrically, being proportionally longest in the largest specimens. In two specimens, P4 is damaged or lost, but in all other specimens, the right side P4 is longest.

Arcotheres boninensis appears to be closest to A. pernicola sharing the longer of the P4 dactyli being longer than the P5 dactylus, the presence of a double row of spinules on the distoflexor margin of the P5 dactylus, an unexpanded distal tip on the cheliped pollex, two well-developed, irregular teeth on the proximal flexor margin of the cheliped pollex, and a proportionally longer Mxp3 dactylus, which reaches to or beyond the tip of the propodus. Unfortunately, uncertainty also surrounds the identity of A. pernicola, whose holotype from the Philippines is in poor condition, being fragmentary and incomplete (Ahyong & Ng, 2007b). What remains of the holotype of A. pernicola, however, accords well with material recently reported from western India and East Africa (Trivedi et al., 2019), and we base our comparisons on this recent material.

Arcotheres pernicola (as presently understood) and A. boninensis appear to be almost indistinguishable, agreeing in almost all the diagnostic characters. The primary difference appears to be in the relative length of the Mxp3 dactylus. Bürger’s (1895: pl. 10 fig. 16) figure of the Mxp3 of A. pernicola depicts the dactylus as reaching the end of the propodus, although in western Indian Ocean material reported by Trivedi et al. (2019: fig. 2F), the dactylus varies from slightly underreaching to reaching the propodus tip as figured by Bürger (1895). In A. boninensis, the dactylus reaches to, or more usually, beyond the tip of the propodus (Fig. 9B), thus partially overlapping with that of A. pernicola. The distributions are also unusual, with no records of A. boninensis and A. pernicola in western Southeast Asia and the northeastern Indian Ocean, where the allied A. purpureus occurs instead. It cannot be excluded that more than one species is included in what is currently regarded as A. pernicola, so until complete material from the Philippines can be compared to A. boninensis and A. purpureus, all three nominal species are retained as separate.

Distribution. Japan, Taiwan, South China Sea (Hainan), New Caledonia, and northwestern Australia.

Arcotheres purpureus (Alcock, 1900)(Figs. 10–15)

Pinnoteres purpureus Alcock, 1900: 339. — Alcock & McArdle, 1902: pl. 62 fig. 6. — Hornell & Southwell, 1909: 102. — Guinot, 1967: 279.

201


Fig. 10. Arcotheres purpureus Alcock, 1900, photographed in life. A, ovigerous females, Pulau Tioman, Malaysia, ZRC 1991.423; B, ovigerous female cl 5.2 mm, cw 7.0 mm, Pulau Weh, Kampung Iboih, Aceh Province, Sumatra, Pulau Weh, ZRC 2019.0515 (photograph by H. H. Tan).

Pinnotheres purpureus. — Borradaile, 1903: 431. — Laurie, 1915: 415. — Tesch, 1918: 250, 253, 287. — Silas & Alagarswami, 1967: 1207, 1214, 1216, 1222. — Schmitt et al., 1973: 6, 10, 83. — Ng et al., 2008: 251. — Ng & Kumar, 2015: 265. — Dev Roy, 2015: 88.

Pinnotheres nigrans Rathbun, 1909: 110. — Rathbun, 1910: 334, figs. 16, 17. — Tesch, 1918: 249, 254. — Gordon, 1936: 173. — Suvatti, 1938: 69. — Suvatti, 1950: 159. — Silas & Alagarswami, 1967: 1203, 1223. — Schmitt et al., 1973: 6, 58. — Naiyanetr, 1980: 42. — Dai et al., 1980: 135, fig. 7. — Dai et al., 1986: 395, 396, fig. 212. — Dai & Yang, 1991: 427, 428, fig. 212. — Naiyanetr, 1998: 104. — Naiyanetr, 2007: 118. — Yang et al., 2008: 809. [New synonymy]

Arcotheres purpureus. — Ng, Clark et al., 2017: 1094. — Trivedi et al., 2018: 61. — Ahyong & Ng, 2020: 337.

Material examined. MALAYSIA: ZRC 1991.422–427, 6 ovigerous females (cl 4.3 mm, cw 5.6 mm to cl 5.4 mm, cw 7.1 mm), Pulau Tioman, Malaysia, from oysters, coll. P. Ng, 15 April 1993; ZRC 1991.428–432, 1 ovigerous female (cl 5.3 mm, cw 6.5 mm), 4 ovigerous females (cl 4.2 mm, cw 4.9 mm to cl 4.8 mm, cw 6.0 mm), Pulau Tulai, 1982 or 1983; ZRC 2018.1394 (with vial of zoea 1, 1985.1894), 6 ovigerous females (cl 4.5 mm, cw 5.7 mm to cl 5.2 mm, cw 6.9 mm), Pulau Tulai, 4 September 2000. THAILAND: ZMUC CRU-9395, ovigerous female (cl 6.6 mm, cw 8.2 mm), Koh Lan (west of Koh Chang), 9 March 1900 (holotype of Pinnotheres nigrans Rathbun, 1909). INDONESIA: ZRC 2019.0515, 1 ovigerous female (cl 5.2 mm, cw 7.0 mm), Pulau Weh, Kampung Iboih, Aceh Province, Sumatra, Pulau Weh, 05°52.895′N, 95°14.708′E, intertidal, inside shingle oyster, THH19-01, coll. H.H. Tan & J.C.E. Mendoza, 10–14 February 2019.

Description of female. Carapace slightly wider than long, transversely ovate to semi-oblong, inflated; front weakly produced, anterior margin slightly convex in dorsal view; anterolateral margins poorly defined; dorsum smooth, glabrous; dorsal surface convex in profile. Epistome with narrow interantennular septum; median buccal margin with acute, triangular, median point. Antennular sinus slightly larger than orbit; antennules folded slightly obliquely. Antennal articles 1 and 2 fused to epistome. Eyes partially visible in dorsal view, filling orbit, cornea pigmented.

Mxp3 ischiomerus length about twice width; outer margin strongly convex; inner proximal margin weakly convex, almost straight; inner distal margin obtusely rounded. Carpus slightly shorter than propodus. Propodus tapering in distal half, apex rounded, dorsally and distally setose. Dactylus digitiform, distally setose, inserted slightly proximal to propodal midlength, apex not reaching end of propodus. Exopod inner margin almost straight, outer margin convex; flagellum with 2 articles, distally setose.

Chelipeds symmetrical from left to right, surfaces glabrous except inner, lower distal margin. Dactylus and pollex relatively straight, crossing distally, without gape; apices expanded mesially. Dactylus occlusal margin with small blunt triangular tooth proximal to midlength, margin straight in distal half, finely denticulate, sparsely setose. Pollex

occlusal margin almost straight, finely denticulate, sparsely setose; with fringe of short setae on inner ventral margin. Propodus palm dorsal margin 2.0–2.2× height, 1.2–1.5× length of dactylus; palm ventral margin almost straight. Carpus unarmed.

P2–5 unarmed, largely glabrous, densest on P5 dactylus. P2, 3, and 5 similar, symmetrical from left to right; left P4 length 1.1× longer than right; relative lengths in decreasing order: P4 > P5 > P3 > P2. Longer P4 merus about 0.5–0.6× pcl. P2–3 dactylus about 0.5× propodus length, evenly arcuate, distally spiniform; P2 flexor margin unarmed; P3 dactylus slightly longer than P2, flexor margin minutely denticulate. P4 dactylus of both sides slender, weakly curved, unarmed, at least 0.7× propodus length. P5 dactylus as long as propodus, slender, weakly curved, slightly shorter than longer P4 dactylus; surfaces covered in short setae, longer setae on flexor margin; flexor distal margin with single row of spines, otherwise unarmed. Relative dactylus lengths: P4 ~ P5 > P3 > P2.

Thoracic sternum anterior margin convex to sinuous medially; sternites 1–3 indistinguishably fused.


202


Fig. 12. Arcotheres purpureus Alcock, 1900, female, cl 4.3 mm, cw 5.6 mm, Tioman, Malaysia, ZRC 1991.423. A, overall habitus; B, ventral view of cephalothorax; C, frontal view of cephalothorax; D, outer view of left chela.

Fig. 11. Arcotheres purpureus Alcock, 1900, female (after Alcock & McArdle, 1902: pl. 62 fig. 6). A, dorsal habitus; B, anterior cephalothorax; C, left maxilliped 3.

203


Fig. 13. Arcotheres purpureus Alcock, 1900, ovigerous female holotype of Pinnotheres nigrans (Rathbun, 1909), cl 6.6 mm, cw 8.2 mm, Koh Lam, Thailand, ZMUC CRU9395. A, overall habitus; B, frontal view of cephalothorax; C, ventral view of cephalothorax.

Remarks. Alcock (1900) and Alcock & McArdle (1902) provided a comparatively good account and good figures of A. purpureus (Fig. 11). Re-examination of the holotype of Pinnotheres nigrans revealed that it is indistinguishable from A. purpureus and they are synonymised. Arcotheres purpureus was described from the Andaman Islands and, based on material reported herein, is now known to range to peninsular Malaysia, Indonesia (Aceh Province), and the Gulf of Thailand. Dai et al. (1980) also reported the species from Hainan Island (as P. nigrans), where it overlaps with A. boninensis. Records from the Maldives (Borradaile, 1903), Red Sea, and Djibouti require confirmation; these might be based on A. pernicola, which has also been recorded from the western Indian Ocean (Trivedi et al., 2019). Arcotheres purpureus reported by Mohanty et al. (2018) from the Devi Estuary, Bay of Bengal, is based on what appears to be a species of Nepinnotheres similar to N. affinis (Bürger, 1895), judging from the figures provided; it is clearly not referrable to A. purpureus.

Although the type material of A. purpureus requires re-examination, the species is redescribed herein to facilitate more detailed comparison with other species of the genus. In the few specimens of A. purpureus that were sufficiently complete for determination, the left P4 was longer than the right, contrasting with A. boninensis, in which the right P4 appears to be longer. Whether the asymmetry of P4 is consistently handed in A. boninensis and A. purpureus remains to be determined by examination of a larger series of both species. The P4 dactylus of A. purpureus was at least 0.7× the respective propodus length, but given that many specimens had broken P4 dactyli, the degree of variation is currently difficult to assess.

As discussed under the account of Arcotheres boninensis, A. purpureus is a member of the A. boninensis group. Within the group, A. purpureus is closest to A. boninensis and A. pernicola, differing by a proportionally shorter Mxp3 dactylus that does not reach beyond the tip of the propodus (Figs. 14B, 15B) (versus dactylus reaching to or beyond the tip

204


Fig. 14. Arcotheres purpureus (Alcock, 1900), ovigerous female holotype of Pinnotheres nigrans (Rathbun, 1909), cl 6.6 mm, cw 8.2 mm, Koh Lam, Thailand, ZMUC CRU9395. A, dorsal habitus; B, right maxilliped 3; C, anterior cephalothorax; D, anterior thoracic sternum; E, right chela, lateral view; F, right chela pollex, dorsal view; G, left P4; H–J, right P3–5, respectively. Scale: A = 2.0 mm; B = 0.5 mm; C–J = 1.0 mm.

in A. boninensis and A. pernicola; Fig. 9B; Trivedi et al., 2019: fig. 2F), the presence of a single row of spinules on the distoflexor margin of the P5 dactylus (Figs. 14J, 15I) (versus two rows in A. boninensis and A. pernicola; Fig. 9N), the palm of the female chela is proportionately more elongate (Figs. 12D, 14E, 15E) (versus distinctly shorter in A. boninensis and A. pernicola; Figs. 8D, 9F; Trivedi

et al., 2019: fig. 2D, E), and an expanded distal tip on the cheliped pollex (Figs. 14F, 15F) (versus unexpanded in A. boninensis and A. pernicola; Fig. 9F; Trivedi et al., 2019: fig. 2D, E). The carapace of A. purpureus also appears to have somewhat straighter lateral margins (Figs. 11A, 12A, 13A, 14A, 15A) than in A. boninensis (Figs. 8A, 9A).

205


Fig. 15. Arcotheres purpureus (Alcock, 1900), ovigerous female, cl 5.7 mm, cw 7.0 mm, Tioman Island, Malaysia, ZRC 1991.422–427. A, dorsal habitus; B, right maxilliped 3; C, anterior cephalothorax; D, anterior thoracic sternum; E, right chela, lateral view; F, right chela pollex, dorsal view; G, left P2; H–I, left P4–5, respectively; J–M, right P2–5, respectively. Scale: A = 2.0 mm; B = 0.5 mm; C–M = 1.0 mm.

Distribution. Western Southeast Asia, from Indonesia, Malaysia, the Gulf of Thailand, and the Andaman Sea; possibly from the western Indian Ocean.

Arcotheres similis (Bürger, 1895)(Fig. 16)

Pinnotheres similis Bürger, 1895: 373, 374, fig. 14. — Chhapgar, 1957b: 42. — Silas & Alagarswami, 1967: 1210, 1216, 1219. — Schmitt et al., 1973: 86.

Pinnotheres kamensis Rathbun, 1909: 110. — Rathbun, 1910: 335, figs. 18, 19. — Tesch, 1918: 249, 252. — Suvatti, 1938: 69. — Suvatti, 1950: 159. — Silas & Alagarswami, 1967: 1200, 1223, 1225. — Schmitt et al., 1973: 50. — Naiyanetr, 1980: 42. — Naiyanetr, 1998: 104. — Naiyanetr, 2007: 118. [New synonymy]

Pinnotheres spinidactylus Gordon, 1936: 169, figs. 1, 2. — Griffin & Campbell, 1969: 157, figs. 7, 8. — Stephenson et al., 1970: 492. — Jones, 1990: 202. — Davie, 2002: 434.

Arcotheres spinidactylus. — Ahyong & Brown, 2003: 10.Arcotheres similis. — Ahyong & Ng, 2007b: 207, 208, fig. 14. —

Ng et al., 2008: 248.Not Arcotheres similis. — Ahyong & Brown, 2003: 9, 10 [=

Arcotheres latus (Bürger, 1895)]

Material examined. ZMUC CR-9396, juvenile male (cl 1.6 mm, cw 1.8 mm), west of Koh Kam, 5 fm (= 9 m), coll. Th. Mortensen, 6 February 1900 (holotype of Pinnotheres kamensis Rathbun, 1909); NHM 1936.6.19.2, 1 ovigerous female (cl 5.5 mm, cw 6.7 mm), Siglap, Singapore, from Modiolus philippinarum, coll. R. Winckworth (holotype

206


Fig. 16. Arcotheres similis (Bürger, 1895), juvenile male holotype of Pinnotheres kamensis Rathbun, 1909, cl 1.6 mm, cw 1.8 mm, west of Koh Kam, Thailand, ZMUC CR-9396. A, dorsal habitus; B, left maxilliped 3; C, lower buccal margin; D, anterior thoracic sternum; E, pleon; F, right chela; G–J, right P2–5, respectively. Scale: A = 1.0 mm; B = 0.25 mm; C–J = 0.5 mm.

of Pinnotheres spinidactylus Gordon, 1936); NHM 1936.6.19.3–7, 1 male (cl 3.3 mm, cw 3.3 mm), 4 ovigerous females (cl 4.7 mm, cw 5.8 mm to cl 5.8 mm, cw 6.7 mm), Siglap, Singapore, from Modiolus philippinarum, coll. R. Winckworth (paratypes of P. spinidactylus Gordon, 1936).

Description of holotype of Pinnotheres kamensis. Carapace subcircular, slightly longer than wide, widest at midlength, weakly arched; pterygostomial surface glabrous. Front produced, anterior margin weakly concave in dorsal view; width about 0.3× cw. Dorsum, glabrous, sparsely punctate. Epistome interantennular septum triangular; median buccal margin with 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 bluntly obtuse. Carpus slightly shorter than propodus. Propodus spatulate, apex rounded, dorsally and distally setose, length almost 3× dactylus length. Dactylus digitiform, distally setose, inserted near propodal midlength, apex not reaching end of propodus. Exopod margins convex; flagellum with 2 articles, distally setose.

207


Chelipeds symmetrical from left to right, glabrous except for inner ventral margin and occlusal margins of dactylus and pollex. Dactylus and pollex relatively curved, crossing distally, with slight gape, apices simple, neither expanded distomesially. Dactylus and pollex occlusal margins straight, sparsely setose, each with blunt triangular tooth proximal to midlength and row of minute finely graded denticles. Pollex distomesial surface with sparse fringe of setae on inner ventral margin. Propodus palm dorsal margin 1.1× height, as long as dactylus; ventral margin gently convex. Carpus unarmed, glabrous.

P2–5 subequal from left to right, unarmed, with natatory setae, otherwise largely glabrous. Relative lengths: P4 > P3 > P2 > P5. Pereopod 2 basis anterior surface smooth. P2–4 dactyli strongly curved, falcate, apex sharp, glabrous or sparsely setose, flexor margin with row of 2–4 minute spines; pereopod 2–4 dactyli 0.6× propodus length. P5 dactylus weakly curved, 0.9× propodus length, sparsely setose, flexor margin with 2 rows of spines. Relative dactylus lengths: P3 = P4 > P2 > 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 2; telson semi-circular, wider than long, wider than anterior margin of somite 6. Pleopods 1 and 2 undeveloped.

Remarks. The identity of Arcotheres similis was significantly clarified by redescription of the type material (Ahyong & Ng, 2007b), prior to which, only the rather minimal type description and inaccurate figure were available (Bürger, 1895). As a result, Gordon’s (1936) record of the species from Singapore proved to be referrable to A. placunicola Ng, 2018, and records from Australia of Ahyong & Brown (2003) were determined as A. latus (Bürger, 1895) (see Ahyong, 2020b). Alongside her misidentified record of A. similis, Gordon (1936) described A. spinidactylus, also from Singapore, notably with a diagnostic row of spinules on the P2–5 dactyli. Ahyong & Ng (2007b), however, observed the singular apparent difference between A. spinidactylus and A. similis to be the presence of one instead of two distoflexor rows of spinules, respectively, on the P5 dactylus, and that Gordon (1936) possibly overlooked the second row in her species. Our re-study of the type material of A. spinidactylus and both sexes of A. similis as part of a wider study of regional Arcotheres (Ng & Ahyong, in preparation) revealed two rows of spinules on the P5 dactylus. Arcotheres spinidactylus and A. similis are indistinguishable and the two species are herein synonymised. As such, A. similis remains in the Singaporean and Australian faunas on the basis of previous records of A. spinidactylus from the respective localities (Gordon, 1936; Griffin & Campbell, 1969; Jones, 1990). Accordingly, the spinulose P2–4 dactyli of males (and often females), on which A. spinidactylus was originally recognised, are now diagnostic of A. similis. Rathbun’s (1924) record of P. similis from Western Australia is probably based on another species given that it was identified based on Bürger’s (1895: pl. 9 fig. 14) inaccurate figure and said to be hosted by an

Ostrea sp. (in Western Australia, currently Crassostrea sp. or Saccostrea sp.). The only Australian pinnotherid currently known to be hosted by ostreids is A. boninensis, which has a proportionally much wider carapace than reported by Rathbun (1924). Rathbun’s (1924) specimen should be re-examined; it could be referrable to (or near) A. shahi Trivedi, Campos & Vachrajani, 2018, from southern India, which resembles Bürger’s (1895) figure of A. similis and is hosted by a species of Crassostrea (Trivedi et al., 2018).

The holotype of Pinnotheres kamensis is a juvenile male and the gonopods are undeveloped. Nevertheless, the spatulate Mxp3 propodus, single row of spinules on the flexor margin of the P2–4 dactylus, and double row of flexor spinules on the P5 dactylus indicate that P. kamensis is referrable to Arcotheres similis (Bürger, 1895), confirming the presence of the species in the Gulf of Thailand. Even as a juvenile, the holotype of P. kamensis agrees closely with mature males of A. similis in all diagnostic features, apart from the gonopods, which are as yet undeveloped. Records of A. similis (as P. spinidactylus; Dai et al., 1980, 1986; Dai & Yang, 1991) from Hainan Island, China, require verification; they appear to represent a different species (Ng & Ahyong, in preparation).

Distribution. Philippines, Indonesia, Malaysia, the Gulf of Thailand, Singapore, Australia, and India.

Arcotheres coarctatus (Bürger, 1895)(Fig. 17)

Pinnotheres coarctatus Bürger, 1895: 369, pl. 9 fig. 7, pl. 10 fig. 7 [type locality: Zamboanga, Philippines, from “Cahebe” = Polymesoda sp.].

Arcotheres coarctatus — Ahyong & Ng, 2007b: 195, fig. 3A. — Ng et al., 2008: 248.

Pinnotheres parvulus — Rathbun, 1910: 331, 332, fig. 13, pl. 2 fig. 9. — Naiyanetr, 1980: 42. — Naiyanetr, 1998: 104. — Naiyanetr, 2007: 118. (not Pinnotheres parvulus Stimpson, 1858).

Material examined. ZMUC 284250, ovigerous female (cl 7.6 mm, cw 8.8 mm), Lem Ngob, mangrove swamp, 23–27 December 1900.

Description of female. Carapace slightly longer than wide, subcircular, sparsely and finely setose anteriorly; front weakly produced, anterior margin transverse in dorsal view; anterolateral margins poorly defined; dorsum smooth, with pair of fine longitudinally arcuate grooves extending from behind eyes to indistinct gastrocardiac groove; dorsal surface convex in profile. Epistome with narrow interantennular septum; median buccal margin with obtuse median point. Antennular sinus slightly larger than orbit; antennules folded slightly obliquely. Antennal articles 1 and 2 fused to epistome. Eyes partially visible in dorsal view, filling orbit, cornea pigmented.

Mxp3 ischiomerus length about twice width; outer margin strongly convex; inner proximal margin convex; inner distal margin bluntly rounded, approximately right-angled. Carpus shorter than propodus. Propodus tapering in distal half, apex

208


Fig. 17. Arcotheres coarctatus (Bürger, 1895), ovigerous female, cl 7.6 mm, cw 8.8 mm, Lem Ngob, Thailand, ZMUC 284250. A, dorsal habitus; B, anterior cephalothorax; C, anterior thoracic sternum; D, right chela; E–H, left P2–5, respectively; I–L, right P2–5, respectively; M, right maxilliped 3. Scale: A = 2.0 mm; B–L = 0.1 mm; M = 0.5 mm.

rounded, dorsally and distally setose. Dactylus digitiform, distally setose, inserted slightly distal to propodal midlength, apex reaching to or slightly beyond end of propodus. Exopod inner margin almost straight, outer margin sinuous; flagellum with 2 articles, distally setose.

Chelipeds symmetrical from left to right, outer surface glabrous to sparsely setose. Dactylus and pollex relatively straight, crossing distally, without gape. Dactylus occlusal margin with blunt triangular tooth proximal to midlength, margin straight in distal half, finely denticulate, sparsely

setose. Pollex occlusal margin with two, blunt triangular teeth proximal to midlength, straight margin in distal half, finely denticulate, sparsely setose; with fringe of short setae on inner ventral margin, extending onto inner surface of palm. Propodus palm dorsal margin 1.4× height, 1.2× length of dactylus; ventral margin almost straight. Carpus unarmed.

P2–5 unarmed, irregularly setose. P2, 3, and 5 similar, symmetrical from left to right; right P4 length 1.3× longer than left; relative lengths in decreasing order: P4 > P5 > P3 > P2. Longer P4 merus about 0.5× pcl. P2–3 dactylus 0.4×

209


propodus length, stout, evenly arcuate, distally spiniform, flexor margin unarmed; P3 dactylus slightly longer than P2. Longer P4 dactylus stout, strait, almost 0.5× propodus length, flexor margin unarmed, strongly setose; shorter P4 dactylus 0.4× propodus length, flexor margin unarmed, strongly setose. P5 dactylus 0.7× propodus length, slender, weakly curved, slightly longer than longer P4 dactylus; setose, longest on flexor margin; flexor distal margin of spines; extensor distal margin with 3 or 4 small denticles, otherwise unarmed. Relative dactylus lengths: P4 > P5 > P3 > P2.

Thoracic sternum anterior margin shallowly concave medially; sternites 1–3 indistinguishably fused.


Remarks. Ahyong & Ng (2007b) transferred P. coarctatus to Arcotheres. Re-examination of Rathbun’s (1910) specimen reported as Pinnotheres parvulus Stimpson, 1858, showed it to be referrable to A. coarctatus, as currently understood, extending the known range of the species westwards to the Gulf of Thailand. Bürger (1895) reported “Cahebe” as the host of P. coarctatus. “Cahebe” appears to be a misspelling of the local name for a commonly harvested brackish water clam (Geloina spp.) (Schmitt et al., 1973). In Tagalog and other Philippine languages, Geloina is known as “kabibe”, for which the old Hispanized spelling would be “cabebe” or “cabibe” depending on the regional patois (JCE Mendoza, pers. comm.).

Distribution. Philippines, Indonesia, and the Gulf of Thailand.

ACKNOWLEDGEMENTS

We are grateful to Danny Eibye-Jacobsen and Jørgen Olesen (ZMUC), for the loan of the Rathbun’s specimens, Paul Clark and Miranda Lowe (NHM) for the loan of the types of Pinnotheres spinidactylus, and the constructive reviews of Ernesto Campos and Tomoyuki Komai, which have improved the manuscript.

LITERATURE CITED

Ahyong ST (2019) First Indonesian Viridotheres Manning, 1996, and redescription of male Afropinnotheres dofleini Manning, 1993, from South Africa (Decapoda, Pinnotheridae). Crustaceana, 92: 107–118.

Ahyong ST (2020a) Discovery of Viridotheres Manning, 1996 in the southwestern Pacific and first record of Discorsotheres camposi Ahyong, 2018 from New Caledonia (Crustacea: Brachyura: Pinnotheridae). Zootaxa, 4763: 429–434.

Ahyong ST (2020b) Resolution of the identity of Pinnotheres latipes Hombron & Jacquinot, 1846 and description of a new species of Viridotheres Manning, 1995: two symbionts of bivalve molluscs. Journal of Crustacean Biology, 40(6): 879–886.

Ahyong ST & Brown DE (2003) Description of Durckheimia lochi n. sp., with an annotated check-list of Australian Pinnotheridae (Crustacea: Decapoda: Brachyura). Zootaxa, 254: 1–20.

Ahyong ST, Komai T & Watanabe T (2012) First Viridotheres Manning, 1996, from Japan, with a key to the species (Decapoda, Brachyura, Pinnotheridae). In: Komatsu H, Okuno J & Fukuoka K (eds.) Studies in Malacostraca: a homage to Masatsune Takeda. Crustaceana Monographs, 17: 35–47.

Ahyong ST & Ng PKL (2005) Review of Durckheimia and Xanthasia, with descriptions of two new genera (Decapoda: Brachyura: Pinnotheridae). Journal of Crustacean Biology, 25: 116–229.

Ahyong ST & Ng PKL (2007a) Visayeres acron, a new genus and species of pinnotherid crab from the Philippines. In: Tan SH & Ng PKL (eds.) Crustacean Supplement I. Raffles Bulletin of Zoology, Supplement 16: 187–189.

Ahyong ST & Ng PKL (2007b) The pinnotherid type material of Semper (1880), Nauck (1880) and Bürger (1895) (Crustacea: Decapoda: Brachyura). In: Tan SH & Ng PKL (eds.) Crustacean Supplement I. Raffles Bulletin of Zoology, Supplement 16: 191–226.

Ahyong ST & Ng PKL (2008) Alain raymondi, a new species of deepwater pinnotherid crab (Crustacea: Decapoda: Brachyura) from the Philippines, commensal with holothurians. Zootaxa, 1919: 61–68.

Ahyong ST & Ng PKL (2020) New species of pinnotherid crabs from Southeast Asia and Papua New Guinea (Crustacea: Decapoda: Brachyura). Zootaxa, 4816: 333–349.

Alcock A (1900) Materials for a carcinological fauna of India. No. 6. Brachyura Catometopa or Grapsoidea. Journal of the Asiatic Society of Bengal, Calcutta, 69(3): 279–486.

Alcock A & McArdle AF (1902) Illustrations of the Zoology of the Royal Indian Marine Survey Ship Investigator, under the command of Commander T.H. Heming, R.N. Crustacea. Part X. Published under the Authority of Captain W. S. Goodridge, R.N., C.I.E., Director of the Royal Indian Marine. Office of the Superintendent of Government Printing, Calcutta, 12 pls. [pls. LVI–LXVII, 1902]

Table 1. Species of pinnotherine crabs studied herein.

Name in Rathbun (1909, 1910) Current name

Pinnotheres bürgeri Rathbun, 1909 Viridotheres buergeri (Rathbun, 1909)Pinnotheres kamensis Rathbun, 1909 Arcotheres similis (Bürger, 1895)Pinnotheres kutensis Rathbun, 1909 Viridotheres buergeri (Rathbun, 1909)Pinnotheres lanensis Rathbun, 1909 Arcotheres lanensis (Rathbun, 1909), new combinationPinnotheres nigrans Rathbun, 1909 Arcotheres purpureus (Alcock, 1900)Pinnnotheres parvulus Stimpson, 1858 Arcotheres coarctatus (Bürger, 1895)Pinnotheres quadratus Rathbun, 1909 Arcotheres quadratus (Rathbun, 1909), new combinationPinnotheres siamensis Rathbun, 1909 Viridotheres buergeri (Rathbun, 1909)

210


Borradaile LA (1903) Marine crustaceans. V. The crabs of the catometope families. In: JS Gardiner (ed.) The fauna and geography of the Maldive and Laccadive Archipelagoes: being the account of the work carried on and of the collections made by an expedition during the years 1899 and 1900. Volume 1, Part 4. Cambridge University Press, Cambridge. Pp. 429–433.

Bürger O (1895) Ein Beitrag zur kenntniss der Pinnotherinen. Zoologische Jahrbücher, Abtheilung für Systematik, Geographie und Biologie der Thiere, 8: 361–390.

Campos E (2001) A new crab species of the genus Arcotheres Manning, 1993, from Thailand (Crustacea, Brachyura, Pinnotheridae). Zoosystema, 23: 493–497.

Chhapgar BF (1957a) On the marine crabs (Decapoda: Brachyura) of Bombay State, part 2. Journal of Bombay Natural History Society, 54(3): 503–549.

Chhapgar BF (1957b) Marine crabs of Bombay State. Contribution No. 1 of the Taraporevala Marine Biological Station Marine Biological Station. Department of Fisheries, Bombay, 89 pp.

Chhapgar BF (1958) On two new species and a variety of crabs (Decapoda: Brachyura) from Bombay state. Records of the Indian Museum, 53: 251–259. [Dated 1955, published 1958]

Dai AY, Feng ZQ, Song YZ & Chen GX (1980) New species and new records of family Pinnotheridae from Hainan Island. Acta Zootaxonomica Sinica, 5: 129–143.

Dai A & Yang S (1991) Crabs of the China Seas. China Ocean Press, Beijing, 682 pp.

Dai A, Yang S, Song YZ & Chen GX (1986) Crabs of the China Seas. China Ocean Press, Beijing, 642 pp.

Davie PJF (2002) Crustacea: Malacostraca: Eucarida (Part 2). In: Wells A & Houston WWK (eds.) Zoological Catalogue of Australia. Volume 19.3B. CSIRO Publishing, Melbourne, 551 pp.

Dev Roy MK (2015) Conservation concerns on crustacean fauna of India. Journal of Environment and Sociobiology, 12: 77–98.

Gordon I (1936) On a few Indo-Pacific species of Pinnotheres, with special reference to asymmetry of the walking legs. Journal of Linnean Society of London, Zoology, 40: 163–180.

Griffin DJG & Campbell BM (1969) The sub-littoral Goneplacidae and Pinnotheridae (Crustacea: Brachyura) of Moreton Bay. Memoirs of the Queensland Museum, 15: 141–164.

Guinot D (1967) La faune carcinologique (Crustacea Brachyura) de l’Océan Indien occidental et de la Mer Rouge. Catalogue, remarques biogéographiques et bibliographie. Mémoires de l’Institut Fondamental d’Afrique Noire, 1966(77): 237–352. [Dated 1966, published 1967]

Hewitt MA (2004) Crustacea (excluding Cirripedia) of the Dampier Archipelago, Western Australia. Records of the Western Australian Museum, Supplement 66: 169–219.

Ho PH & Hung MS (1997) Seashore crabs of Hsin-Chu City. Hsinchu City, Taiwan, 122 pp. [In Chinese]

Hornell J & Southwell T (1909) Description of a new species of Pinnoteres from Placuna placenta, with a note on the genus. In: Hornell J (ed.) Report to the Government of Baroda on the Marine Zoology of Okhamandal in Kattiawar. Part 1. Richard Clay & Sons Ltd., Bungay, Suffolk. Pp. 99–103.

Jones D (1990) Annotated checklist of marine decapod Crustacea from Shark Bay, Western Australia. In: Berry PF, Bradshaw SD & Wilson BR (eds.) Research in Shark Bay. Report of the France–Australe Bicentenary Expedition Committee, 325 pp.

Komai T, Kawai K & Ng PKL (2020) On the identity of the poorly known pea crab, Pinnothera obesa Dana,1852, and description of a new species of Arcotheres Manning, 1993 from the Southwest Pacific (Decapoda: Brachyura: Pinnotheridae). Zootaxa, 4822: 257–268.

Komatsu H (2011) Crabs dredged off the Ogasawara Islands (Crustacea, Decapoda, Brachyura). Memoirs of the National Museum of Natural Science, Tokyo, 47: 219–277.

Konishi K (1996) Some topics on pea crabs of Japan. Cancer, 1996: 15–21.

Konishi K (2010) Some topics on pea crabs of Japan – additional summary after 1996. Cancer, 2010: 31–38.

Laurie RD (1915) Reports on the marine biology of the Sudanese Red Sea.—XXI. On the Brachyura. Journal of the Linnean Society of London, Zoology, 31(209): 407–475, pls. 42–45.

Manning RB (1993) Three genera removed from the synonymy of Pinnotheres Bosc, 1802 (Brachyura: Pinnotheridae). Proceedings of the Biological Society of Washington, 106: 523–531.

Manning RB (1996) Viridotheres marionae, a new genus and species of pinnotherid crab from West Africa (Crustacea: Decapoda: Brachyura). Zoologische Mededelingen, Leiden, 70: 271–273.

Manning RB (1998) A new genus and species of pinnotherid crab (Crustacea, Decapoda, Brachyura) from Indonesia. Zoosystema, 20(2): 357–362.

Marumura M & Kosaka A (2003) Catalogue of the brachyuran and anomuran crabs donated by the late Mr. Seiji Nagai to the Wakayama Prefectural Museum of Natural History. Wakayama Prefectural Museum of Natural History, Kainan, 73 pp.

Miers EJ (1886) Report on the Brachyura collected by H.M.S. Challenger during the years 1873–1876. Report on the Scientific Results of the Voyage of HMS Challenger during the years 1873–76. Zoology, Volume 17. Published by Order of Her Majesty’s Government, pp. i–l, 1–362, pls. I–XXIX.

Miyake S (1983) Japanese Crustacean Decapods and Stomatopods in Color. Volume 2: Brachyura (Crabs). Hoikusha Publishing Co., Osaka, 8 + 277 pp., 64 pls. [In Japanese]

Mohanty B, Raut D, Dev Roy MK, Raman AV, Patnaik L, Nayak A, Rout SS & Dash B (2018) New host record of pea crab Arcotheres purpureus (Alcock, 1900) (Crustacea: Decapoda: Pinnotheridae) with first description of male. Marine Biodiversity Records, 11: 1.

Muraoka K (1998) Catalogue of the brachyuran and anomuran crabs donated by Prof. Dr. Tune Sakai to the Kanagawa Prefectural Museum. Catalogue of the collection in the Kanagawa Prefectural Museum of Natural History, Odawara, (11): 1–67 pp, 16 pls.

Naiyanetr P (1980) Crustacean Fauna of Thailand (Decapoda and Stomatopoda). Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, 73 pp.

Naiyanetr P (1998) Checklist of Crustacean Fauna in Thailand (Decapoda, Stomatopoda, Anostraca, Myodocopa and Isopoda). Office of Environmental Policy and Planning, Bangkok, 161 pp.

Naiyanetr P (2007) Checklist of Crustacean Fauna in Thailand (Decapoda, Stomatopoda, Anostraca, Myodocopa and Isopoda). Office of Natural Resources and Environmental Policy and Planning, Bangkok, 196 pp.

Ng PKL (2014) Indopinnixa shellorum, a new species of pea crab (Crustacea: Brachyura: Pinnotheridae) associated with a sipunculid from Singapore. Raffles Bulletin of Zoology, 62: 696–700.

Ng PKL (2018a) On the identities of Pinnotheres villosissimus Doflein, 1904, P. dofleini Lenz, in Lenz & Strunck, 1914, and P. pilumnoides Nobili, 1906 (Decapoda, Brachyura, Pinnotheridae) from the western Indian Ocean. Crustaceana, 91: 611–633.

Ng PKL (2018b) Arcotheres placunicola, a new species of pea crab (Crustacea: Brachyura: Pinnotheridae) from the window-pane shell, Placuna ephippium Philipsson, 1788 (Placunidae) in Singapore. Raffles Bulletin of Zoology, 66: 474–485.

Ng PKL & Ahyong ST (in preparation) The house of cards that is pinnotherid taxonomy: pea crabs of the genus Arcotheres Manning, 1993 (Crustacea: Brachyura), from Singapore and Peninsular Malaysia, with a reappraisal of diagnostic characters and descriptions of two new genera. Raffles Bulletin of Zoology.

Ng PKL, Ahyong ST & Campos E (2019a) Two new genera of pinnotherid crabs (Crustacea: Brachyura: Pinnotheroidea) from the Americas and the Western Pacific. Raffles Bulletin of Zoology, 67: 337–351.

211


Ng PKL, Ahyong ST & Clark PF (2019b) The identity of Pinnotheres socius Lanchester, 1902 (Decapoda, Brachyura, Pinnotheridae). Crustaceana, 92: 685–692.

Ng PKL, Clark PF, Mitra S & Kumar AB (2017) Arcotheres borradailei (Nobili, 1906) and Pinnotheres ridgewayi Southwell, 1911: a reassessment of characters and generic assignment of species to Arcotheres Manning, 1993 (Decapoda, Brachyura, Pinnotheridae). Crustaceana, 90: 1079–1097.

Ng PKL, Guinot D & Davie PJF (2008) Systema Brachyurorum; Part I. An annotated checklist of extant brachyuran crabs of the world. Raffles Bulletin of Zoology, Supplement 17: 1–286.

Ng PKL & Ho PH (2016a) Orthotheres baoyu, a new species of pea crab (Crustacea: Brachyura: Pinnotheridae) associated with abalones from Tungsha Island, Taiwan; with notes on the genus. Raffles Bulletin of Zoology, 64: 229–241.

Ng PKL & Ho PH (2016b) A new genus for Fabia obtusidentata Dai, Feng, Song and Chen, 1980, a pea crab (Decapoda: Brachyura: Pinnotheridae) symbiotic with the moon scallop Amusium pleuronectes (Linnaeus, 1758) (Mollusca: Pectinidae). Journal of Crustacean Biology, 36: 740–751.

Ng PKL & Kumar AB (2015) A new species of Afropinnotheres Manning, 1993 (Crustacea, Brachyura, Pinnotheridae) from southwestern India, the first record of the genus from the Indian Ocean, with a review of the Pinnotheridae of India and adjacent seas. Zootaxa, 3947: 264–274.

Ng PKL & Manning RB (2003) On two new genera of pea crabs parasitic in holothurians (Crustacea: Decapoda: Brachyura: Pinnotheridae) from the Indo West Pacific, with notes on allied genera. Proceedings of the Biological Society of Washington, 116: 901–919.

Ng PKL & Ngo VT (2010) Solenotheres prolixus, a new genus and new species of pinnotherid crab (Crustacea: Decapoda: Brachyura) associated with the razor clam, Solen corneus Lamarck, 1818 (Solenidae) in Vietnam. Zootaxa, 2570: 61–68.

Ng PKL & Richer de Forges B (2007) The Brachyura of New Caledonia. In: Payri CE & Richer de Forges B (eds.) Compendium of Marine Species from New Caledonia. Documents Scientifiques et Techniques. IRD Noumea, Noumea. Pp. 315–331.

Ng PKL, Shih HT, Ho PH & Wang CH (2017) An updated annotated checklist of brachyuran crabs from Taiwan (Crustacea: Decapoda). Journal of the National Taiwan Museum, 70: 1–185.

Ng PKL, Wang CH, Ho PH & Shih HT (2001) An annotated checklist of brachyuran crabs from Taiwan (Crustacea: Decapoda). National Taiwan Museum Special Publication Series, Number 11: 1–86, 8 colour pls.

Rathbun MJ (1909) New crabs from the Gulf of Siam. Proceedings of the Biological Society of Washington, 22: 107–114.

Rathbun MJ (1910) The Danish expedition to Siam 1899–1900. V. Brachyura. Konelige Danske Videnskabernes Selskat, Naturvidenskabelige Matematiske Afhandlinger, 5: 301–367, pls. 1, 2, map.

Rathbun MJ (1924) Results of Dr. E. Mjöberg’s Swedish Scientific Expeditions to Australia 1910–1913. 37. Brachyura, Albuneidae and Porcellanidae, Arkiv för Zoologi, 16: 1–33.

Sakai T (1933) Taxonomy of the Japanese Pinnotheridae. Botany and Zoology, Scientific and Applied, 1(7): 977–984. [In Japanese]

Sakai T (1936) Crabs of Japan: 66 plates in life colours with description. Sanseido, Tokyo, 239 + 12 (literature cited) + 27 (bibliography and index) pp., 66 pls. [Dated 1935, published 1936]

Sakai T (1939) Studies on the Crabs of Japan. IV. Brachygnatha, Brachyrhyncha. Tokyo, pp. 365–741 + 1–23 (index), text-figs. 1–129, pls. 42–111.

Sakai T (1956) Kani. Shisei Shoin, Tokyo, 60 pp. [in Japanese]

Sakai T (1965) The crabs of Sagami Bay, collected by His Majesty the Emperor of Japan. Maruzen, Tokyo, xvi + 206 pp. (in English), 100 pls., 92 pp. (in Japanese), 32 pp. (bibliography and index, in English and Japanese), 1 map.

Sakai T (1976) Crabs of Japan and the Adjacent Seas. Kodansha, Tokyo, vol. 1, xxxix + 773 pp.; vol. 2, 461 pp.; vol. 3, 16 pp., 251 pls.

Schmitt WL, McCain JC & Davidson E (1973) Decapoda I. Brachyura I. Fam. Pinnotheridae. In: Gruner H-E & Holthuis LB (eds.) Crustaceorum Catalogus. Pars 3. W. Junk B.V., Den Haag, 160 pp.

Silas EG & Alagarswami K (1967) On an instance of parasitisation by the pea-crab (Pinnotheres sp.) on the backwater clam [Meretrix casta (Chemnitz)] from India, with a review of the work on systematics, ecology, biology and etiology of pea crabs of the genus Pinnotheres, Latreille, 1802. Proceedings of the Symposium on Crustacea held at Ernakulam, 1965, Symposium Series 2. Marine Biological Association of India, 3: 1161–1227.

Stephenson W, Williams WT & Lance GN (1970) The macrobenthos of Moreton Bay. Ecological Monographs, 40: 459–494.

Stimpson W (1858) Prodromus descriptionis animalium evertebratorum quoe in Expeditione ad Oceanum Pacificum eptentrionalem a Republica Federata Missa, Cadwaladaro Ringgold et Johann Rodgers Ducibus, observavit et descripsit - Part V, Crustacea Ocypodoidea. Proceedings of the Academy of Natural Science, Philadelphia, 9: 93–110.

Stimpson W (1907) Report on the Crustacea (Brachyura and Anomura) collected by the North Pacific Exploring Expedition 1853–1856. Smithsonian Miscellaneous Collections, part of 49(1717): 1–240, 26 pls.

Suvatti C (1938) A check-list of aquatic fauna in Siam (excluding fishes). Bureau of Fisheries, Bangkok, 116 pp.

Suvatti C (1950) Fauna of Thailand. Department of Fisheries, Bangkok, ii + 1100 pp., 1 pl.

Suzuki H (1972) Freshwater and commensal crustacean decapods from the Bonin Islands. Science reports of the Yokohama National University, Section II, Biological and Geological Sciences, 19: 1–26.

Takeda M (1982) Keys to the Japanese and foreign crustaceans fully illustrated in colors. Hokuryukan, Tokyo, 284 pp.

Takeda M (1993) Catalogue of Crab Specimens (Crustacea: Decapod: Brachyura) (Part 1). National Science Museum, Tokyo, 81 pp.

Takeda M & Konishi K (1988) Redescription of Pinnotheres alcocki Rathbun, 1909, a commensal pea crab new to Japan. Bulletin of the National Science Museum, Tokyo, series A, 14: 137–144.

Tesch JJ (1918) Decapoda Brachyura II. Goneplacidae and Pinnotheridae. Siboga Expeditie Monographie, 39c1: 149–295, pls. 7–18.

Trivedi JN, Gosavi S, Vachhrajani KD, Mitra S, Ravinesh R & Ng PKL (2020) On the identities of Nepinnotheres vicajii (Chhapgar, 1957) and Arcotheres casta (Antony & Kuttyamma, 1971) from western India: conspecificity and taxonomy (Decapoda, Brachyura, Pinnotheridae). Zootaxa, 4809(3): 496–508.

Trivedi JN, Gosavi S, Vachhrajani KD & Ng PKL (2019) Redescription of Arcotheres pernicola (Bürger, 1895) (Crustacea: Decapoda: Brachyura: Pinnotheridae) from the oyster Magallana gryphoides (Schlotheim, 1820) in India. Zootaxa, 4706(4): 587–593.

Trivedi JN, Trivedi DJ, Vachhrajani KD & Ng PKL (2018) An annotated checklist of the marine brachyuran crabs (Crustacea: Decapoda: Brachyura) of India. Zootaxa, 4502: 1–83.

Yang S, Chen HL & Jian W (2008) Infraorder Brachyura Latreille, 1803. In: Liu JY (ed.) Checklist of marine biota China seas. Science Press, Academia Sinica, Beijing. Pp. 761–809.