Arcotheres placunicola Ng, 2018a

Ng, Peter K. L. & Ahyong, Shane T., 2022, The pea crab genus Arcotheres Manning, 1993 (Crustacea: Brachyura: Pinnotheridae) from Singapore and Peninsular Malaysia, with a reappraisal of diagnostic characters and descriptions of two new genera, Raffles Bulletin of Zoology 70, pp. 134-248 : 207-215

Arcotheres placunicola Ng, 2018a

( Figs. 57–62 )

Pinnotheres similis — Tesch, 1918: 254 (list); Gordon, 1936: 172, fig. 3 ( Singapore); Silas & Alagarswami, 1967: 1210 (list) (not Pinnotheres similis Bürger, 1895 ).

Arcotheres palaensis — Pohle & Marques, 1998: 231 (part) (not Pinnotheres palaensis Bürger, 1895 ).

Arcotheres placunicola Ng, 2018a: 475 , figs. 1–6 [type locality: Changi, Singapore]; De Gier & Becker, 2020: tab. 1.

Type material. Holotype: ovigerous female (11.2 × 8.6 mm) ( ZRC 2017.1009 ), off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, coll. S. K. Tan et al., 7 June 2016 . Paratypes: 5 males (5.6 × 4.7 mm, 4.7 × 4.1 mm, 4.0 × 3.7 mm, 3.9 × 3.6 mm, 3.6 × 3.4 mm), 4 ovigerous females (10.4 × 8.3 mm, 8.7 × 7.5 mm, 7.5 × 6.1 mm, 7.0 × 5.5 mm), 1 female (8.8 × 6.9 mm), 3 females (with rhizocephalans) (8.6 × 6.3 mm, 8.6 × 7.1 mm, 9.0 × 6.9 mm), 2 juvenile females (3.6 × 2.9 mm, 6.2 × 5.1 mm) ( ZRC 2017.1010 ), same data as holotype ; 14 males (largest 5.1 × 4.4 mm, smallest 2.4 × 2.3 mm), 2 males (with rhizocephalans) (5.7 × 4.7 mm, 5.5 × 5.0 mm), 16 ovigerous females (largest 10 × 8.7 mm, smallest 7.7 × 6.3 mm), 1 ovigerous female (10.1 × 8.0 mm), 10 non-ovigerous females (largest 10.3 × 7.8 mm, smallest 5.4 × 4.5 mm), 2 females (with rhizocephalan) (6.3 × 4.9 mm, 7.8 × 5.8 mm), 1 juvenile female (3.8 × 3.7 mm) ( ZRC 2017.1012 ), off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, coll. S. K. Tan et al., 8 June 2016 ; 1 male (4.2 × 3.8 mm), 2 ovigerous females (7.2 × 6.1 mm, 7.5 × 6.2 mm) ( ZRC 2012.432 ), off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, coll. P. K. L. Ng et al., 5 July 2012 ; 4 ovigerous females (largest 9.1 × 7.4 mm, smallest 6.5 × 5.4 mm), 3 non-ovigerous females (largest 8.9 × 6.9 mm, smallest 8.1 × 6.7 mm), 2 females (with rhizocephalan) (8.2 × 7.3 mm, 11.2 × 9.1 mm) ( ZRC 2017.1013 ), off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, coll. P. K. L. Ng & P. Y. C. Ng, June 2016 ; 2 males (2.2 × 2.2 mm, 2.4 × 2.4 mm) ( ZRC 2017.1014 ), Tanah Merah Ferry Terminal Beach, near Changi Point, coll. S. K. Tan et al., 17 November 2016 ; 1 male (with rhizocephalan) (5.6 × 5.1 mm), 3 ovigerous females (7.3 × 5.9 mm, 8.0 × 6.1 mm, 9.5 × 7.2 mm), 1 non-ovigerous female (with rhizocephalan) (9.0 × 7.4 mm) ( ZRC 2017.1015 ), off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, coll. P. K. L. Ng & P. Y. C. Ng, 31 March 2017 ; 1 male (with Sacculina ) (4.8 × 4.5 mm) ( ZRC 2017.1016 ), off Changi beach, adjacent to National Service Recreational Country Club, coll. H. H. Tan et al., 26 May 2017 ; 4 females, 1 juvenile female ( ZRC 2017.1011 ) , 1 male, 2 ovigerous females ( AM P105907 ), off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, coll. S. K. Tan et al., 5 July 2017 ; 1 male (with rhizocephalan), 3 females ( AM P105908 ), intertidal area, off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, coll. S. K. Tan et al., 26 June 2017 ; 1 female ( ZRC 2017.1265 ), Telok Paku , beach, in “ Placuna sella ”, coll. 8 April 1965 . All locations in Singapore .

Other material examined. Singapore: 3 males, 6 females ( ZRC 2019.1113 ), probably in Placuna ephippium , intertidal area, off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, Singapore, coll. P. K. L. Ng et al., 3 August 2012 ; 1 female ( ZRC 2019.1021 ), intertidal area, off Changi beach, next to Carpark 6, Singapore, coll. H. H. Tan et al., 24 December 2018 ; 1 female ( ZRC 2019.1037 ), intertidal area, off Changi beach, next to Carpark 7, near ferry terminal, 1.374223°N, 104.006827°E, Singapore, coll. H. H. Tan et al., 4 July 2019 ; 1 female (11.6 × 8.6 mm), 1 juvenile female ( ZRC 2021.80 ), inside Placuna ephippium, Changi Bay , ex Red Cliff Shoal area , Singapore, coll. S. K. Tan et al., 13 January 2021 . Peninsular Malaysia: 1 male (3.7 × 3.3 mm) ( ZRC 2021.802 , ex part ZRC 2000.2613 ), Batu Pahat , Johor, supposedly from Tegillarca granosa , mangroves, coll. H. K. Tan, 16 August 1983 ; 1 male, 3 females, 1 juvenile female ( ZRC 2009.905 ), supposedly from Tegillarca , Pahang, coll. students, Universiti Teknologi Malaysia, 2006 .

Description. Carapace and pereopods well chitinised. Female: Carapace subcircular to subhexagonal, distinctly wider than long; dorsal and lateral surfaces smooth, glabrous; front usually projecting anteriorly beyond orbits, entire, margin slightly convex; anterior quarter of anterolateral margin gently sloping posteriorly, forming angle with rest of convex margin ( Fig. 58A ). Eyes small, not visible in dorsal view; mobile, completely filling orbit ( Fig. 58A–C ). Epistome with median part triangular, lateral margins gently concave ( Fig. 58C ).

MXP3 outer surface with scattered short setae; ischiomerus completely fused, subrhomboidal, inner margin angular at widest point; carpus short; propodus about 3 times as long as high, subspatulate, distinctly longer than carpus; dactylus slender, inserted at midlength of propodus, tip not reaching propodal apex; exopod relatively slender, about one-third length of ischiomerus, flagellum 2-segmented ( Fig. 59A, B ).

Chela slender, dactylus almost two-thirds palm length; palm slender, proximally narrower than distally; outer surface of palm, fingers (except for distal part) almost glabrous, with only scattered short setae; dactylus occlusal margin with large subproximal tooth; pollex occlusal margin with 1 low proximal tooth, 1 submedian tooth; tips of fingers sharp, hooked ( Figs. 58D , 59C ).

P2–P5 dorsally, ventrally unarmed; outer surface covered with scattered, very short setae or glabrous; ventral margins of propodus and dactylus more setose; merus relatively longer, more slender, relative lengths of meri P4>P3>P5>P2; left (sometimes right) P4 distinctly the longer; P2 and P3 dactyli short, subequal, tip gently hooked, half propodus length; P4 dactylus elongate, weakly falciform, three-fourths propodus length, longer than P2 and P3 dactyli, shorter than P5 dactylus; P5 merus 4.3–4.4 times longer than wide; P5 dactylus longest, longer than propodus, distal half covered with short setae, ventral margin of distal part with 2 rows of up to 11 spinules each, lower row usually with few spinules, lower and upper rows with subequal number of spinules ( Fig. 50D–K ”).

Pleon extending to buccal region, covering bases of P2–P5; telson recessed into distal margin of somite 6 ( Fig. 58B ).

Male: Carapace almost circular, slightly wider than long; dorsal surface covered with scattered short setae or smooth, slightly convex to almost flat; front distinctly projecting anteriorly, margin gently sinuous ( Figs. 60A, D , 62A ). Eyes distinctly visible in dorsal view ( Figs. 60A, D , 62A ). MXP3 as in female ( Figs. 61D , 62C ). Anterior thoracic sternum wide, sternites 1, 2 fused, partially sunken into buccal cavity; suture between sternites 2 and 3 shallow; sternites 3, 4 completely fused, separated only by shallow grooves; sternopleonal cavity reaching to junction between sternites 3 and 4. Chela relatively stouter, shorter than in female, tip of fingers longer ( Figs. 60C, F , 61A , 62D ). P2–P5 dorsally, ventrally unarmed; outer surface covered with short setae; carpus and propodus with long natatory setae; left and right meri equal, relative lengths of meri P4>P3>P2>P5; dactyli of P2–P4 progressively longer; left (sometimes right) P4 dactylus slightly longer, more slender than right side; P4 and P5 dactyli subequal to that of P3, completely covered with short setae ( Figs. 61E–L , 62E –L’); P5 dactylus with 2 rows of up to 11 or 12 distoflexor spinules each ( Figs. 60H , 61L ). Pleon slender, triangular, widest at somite 3, lateral margins of somite 4 distinctly concave, tapering distally to telson; telson subquadrate-linguiform with convex lateral margins, wider than long ( Figs. 61B, C , 62B ). G1 relatively stout, arcuate, curved outwards, short extended tip gently curved upwards or straight ( Figs. 60G , 61M, N, Q , 62M, N ). G2 short, with spatuliform tip; exopod almost as long as endopod ( Figs. 61O, P , 62O ).

Variation. Several female specimens have the frontal margin weakly projecting, being almost level with the anterolateral margin, making the carapace appear more evenly ovate ( Fig. 58A ). Significantly, the male pleon changes shape (notably somite 6 and telson) with size, with somite 6 becoming proportionally narrower and the telson less tapering with increasing body size ( Figs. 61B, C , 62B ). The G 1 in A. placunicola varies slightly, with the tapering tip generally longer in larger males ( Fig. 61M, N ) and relatively shorter in some smaller males ( Fig. 61Q ), but also sometimes long in small specimens ( Figs. 60G , 62M, N ).

Colour. Rather variable: females pale yellow to orange or dirty white with brown patterns; males more uniform brown to greenish brown ( Fig. 57F ).

Host. Known with certainty only from Placuna ephippium (Philipsson, 1788) ( Placunidae Rafinesque, 1815 ). One lot (ZRC 2009.905) of A. placunicola collected in 2006 from Pahang, Malaysia, as part of aquaculture surveys by students from the Universiti Teknologi Malaysia, were labelled as collected from “ Anadara ”. We suspect the host was incorrectly recorded.

Remarks. Arcotheres placunicola most closely resembles A. palaensis and A. similis , with which it has been confused (see Ng, 2018a). Arcotheres placunicola and A. similis are superficially similar, with similar MXP3 and P5 morphology, so the two species can be easily mistaken if not examined carefully. The female carapaces of the two species are superficially similar but can usually be distinguished, especially with fresh material. In A. placunicola ( Figs. 57A–D , 58A ), the carapace shape is more polygonal, with the anterolateral corners of the carapace bluntly angular, contrasting with the more rounded carapace of A. similis ( Figs. 27A, C , 28A, C ), in which the anterolateral corners are evenly curved. As discussed earlier, carapace shape can change to varying degrees when preserved. That being said, there is some overlap in carapace shape between the two species, so other characters must also be checked to confirm identifications. The female P2 and P3 dactyli also differ in shape, being evenly curved in A. similis ( Fig. 30A, B, E, F ), and tightly curved distally with a more falcate apex in A. placunicola ( Fig. 59D, E, H, I ). While the P5 dactylus of both species possess two rows of distoflexor spinules, in A. placunicola , the lower row is shorter and usually has only a few more spinules than the upper row, the two rows often with subequal numbers of more closely packed spinules ( Fig. 59 G’, K’, K”). In A. similis , on the other hand, the lower row is almost always long, with distinctly more, widely spaced spinules ( Fig. 30 D’, H’, L).

Males of A. placunicola and A. similis are quite different. Compared to A. similis , the carapace of A. placunicola is distinctly more transversely ovate with the dorsal surface gently convex to almost flat ( Figs. 60A, B, E , 62A ) (versus carapace round or longitudinally ovate with the dorsal surface inflated and distinctly convex in A. similis ; Figs. 31A, B, D , 32A ). The G1 of A. placunicola and A. similis are superficially similar, but that of A. placunicola is more evenly curved with the slender apical projection directed oblique to the main axis ( Figs. 60G , 61M, N, Q , 62M, N ), while in A. similis , the median and subdistal parts are almost straight and the apical projection almost in line with the main axis ( Figs. 32L–N , 33E–H, J, K ). Arcotheres placunicola closely resembles A. palaensis in the structure of the carapace, P2 and P3 dactyli, MXP3, and G1, but adults can be distinguished by the relatively longer P2–P5 (P5 merus 4.3–4.4 times longer than wide, versus 3.6–4.0 times in A. palaensis ) and by the P5 dactylus possessing two rows of distoflexor spinules ( Fig. 59 G’, K’, K”) (versus absent in A. palaensis ). The adult chela is also usually relatively longer and more slender in A. placunicola , with the proximal part more narrow than the distal section ( Fig. 59C ); it is often proportionately and evenly stouter in A. palaensis ( Figs. 5D , 6D ), although the palm may also be elongated ( Fig. 4A, B ; Ahyong & Ng, 2007b: fig. 9B). The MXP3 of A. placunicola usually has a proportionately shorter dactylus ( Fig. 59A, B ), but it varies too much in A. palaensis ( Fig. 13 ) to reliably distinguish the two species. The G1 of A. placunicola and A. palaensis are also superficially similar, although that of A. placunicola is slightly more curved as well as relatively shorter and stouter ( Figs. 60G , 61M, N, Q , 62M, N ) (cf. Fig. 22K–M for A. palaensis ).

Arcotheres exiguus also superficially resembles A. placunicola , especially with regards to the general carapace shape and relatively longer P2–P5. Female A. placunicola , however, can be reliably distinguished by the P5 dactylus possessing a double row of subdistal spinules on the ventral margin ( Fig. 59 G’, K’, K”) (versus absent in A. exiguus ; Fig. 40G ); and the chela is often proportionately longer and more slender proximally than distally ( Figs. 58D , 59C ) (versus short and stout in A. exiguus ; Fig. 40C ). In addition, the frontal margin of A. placunicola is relatively wider and curves gently to join the anterolateral margin ( Fig. 58A ) (versus shorter frontal margin which joins lateral margins at a sharper angle in A. exiguus ; Fig. 40A ).

Distribution. South China Sea from Singapore and Peninsular Malaysia.

Figures

Fig. 57. Arcotheres placunicola Ng, 2018, colour in life, after Ng (2018a: figs. 5, 6). A, paratype female (size not known) (ZRC 2017.1010); B, paratype ovigerous female (8.0 × 6.1 mm) (ZRC 2017.1015); C, paratype non-ovigerous female with rhizocephalan (9.0 × 7.4 mm) (ZRC 2017.1015); D, paratype ovigerous female (7.3 × 5.9 mm) (ZRC 2017.1015); E, paratype female (8.8 × 6.9 mm) (ZRC 2017.1010), Changi, Singapore; F, paratype male (4.7 × 4.1 mm) (ZRC 2017.1010); G, paratype male with rhizocephalan (5.6 × 5.1 mm) (ZRC 2017.1015); H, paratype ovigerous female (7.3 × 5.9 mm) (ZRC 2017.1015), in situ on Placuna (crab indicated by arrow). All specimens from Singapore.

Fig. 58. Arcotheres placunicola Ng, 2018, holotype ovigerous female (11.2 × 8.6 mm) (ZRC 2017.1009), Changi, Singapore; after Ng (2018a: fig. 1). A, overall dorsal view; B, ventral view of cephalothorax; C, frontal view of cephalothorax; D, outer view of left chela.

Fig. 59. Arcotheres placunicola Ng, 2018, after Ng (2018a: fig. 3). A, C, E–K, holotype ovigerous female (11.2 × 8.6 mm) (ZRC 2017.1009), Changi, Singapore; B, D, paratype ovigerous female (10.1 × 8.0 mm) (ZRC 2017.1012), Changi, Singapore. A, B, outer view of right MXP3; C, left chela and carpus; D–G, left P2–P5, respectively; G’, distal part of dactylus of left P5 showing stiff subdistal spinules (dorsal view, soft setae omitted); H–K, right P2–P5, respectively; K’, distal part of dactylus of right P5 showing stiff subdistal spinules (ventral view, soft setae omitted); K”, distal part of dactylus of left P5 showing stiff subdistal spinules (dorsal view, soft setae omitted). Scales = A, B, G’, K’, K”, 0.5 mm; C–K, 1.0 mm.

Fig. 60. Arcotheres placunicola Ng, 2018. A–C, paratype male (5.6 × 4.7 mm) (ZRC 2017.1010), Changi, Singapore; D–H, male (3.7 × 3.3 mm) (ZRC 2021.802), Batu Pahat, Peninsular Malaysia. A, D, overall dorsal view; B, E, frontal view of cephalothorax; C, F, outer view of left chela; G, left G1; H, distal part of P5 (ventral view). B after Ng (2018a: fig. 2B).

Fig. 61. Arcotheres placunicola Ng, 2018, after Ng (2018a: fig. 4). A, B, D–P, paratype male (5.6 × 4.7 mm) (ZRC 2017.1010); C, Q, paratype young male (2.4 × 2.4 mm) (ZRC 2017.1014). Both specimens from Changi, Singapore. A, right chela and carpus (setae omitted); B, C, male pleon; D, right MXP3 (setae omitted); E–H, right P2–P5, respectively; I–L, left P2–P5, respectively (setae omitted); L’, distal part of P5 dactylus (dorsal view, soft setae omitted); M, Q, left G1 (ventral view, setae omitted); N, left G1 (dorsal view, setae omitted); O, left G2 (setae omitted); P, right G2 (mesial view showing exopod, setae omitted). Scales = A, B, E–L, 1.0 mm; D, M–P, 0.5 mm; C, L’, Q, 0.25 mm.

Fig. 62. Arcotheres placunicola Ng, 2018, male (3.7 × 3.3 mm) (ZRC 2021.802), Batu Pahat, Peninsular Malaysia. A, dorsal view of carapace; B, pleon (setae omitted); C, outer view of left MXP3 (setae denuded); D, outer view of left chela; E–H, left P2–P5, respectively (setae omitted); I–L, right P2–P5, respectively; M, left G1 (ventral view); N, left G1 (dorsal view, setae omitted); O, left G2. Scales = A, B, D–L, 0.5 mm; C, M–O, 0.2 mm.

Fig. 50. Right female P5. A–G, Arcotheres exiguus (Bürger, 1895), Peninsular Malaysia: A, juvenile (3.8 × 3.6 mm) (ZRC 2018.772); B, ovigerous (4.5 × 4.1 mm) (ZRC 2018.775); C, non-ovigerous (4.6 × 4.2 mm) (ZRC 2018.772); D, spent (5.4 × 4.6 mm) (ZRC 2018.775); E, ovigerous (6.8 × 6.1 mm) (ZRC 2019.516); F, ovigerous (7.7 × 6.7 mm) (ZRC 2018.772); G, ovigerous (8.9 × 7.6 mm) (ZRC 2018.775). H–L, A. rayi Ahyong & Ng, 2007, Peninsular Malaysia: H, juvenile (5.4 × 5.8 mm) (ZRC 2013.1416); I, non-ovigerous (5.6 × 4.3 mm) (ZRC 2013.1416); J, non-ovigerous (8.1 × 5.2 mm) (ZRC 2013.1416); K, spent (6.9 × 5.2 mm) (ZRC 2013.1416); L, ovigerous (8.4 × 7.0 mm) (ZRC 2013.1416). Scale = 1.0 mm.

Fig. 27. Arcotheres similis (Bürger, 1895), female (6.7 × 5.5 mm) (NHM 1936.6.19.2), Singapore (holotype female of Pinnotheres spinidactylus Gordon, 1936). A, overall dorsal view; B, ventral view of cephalothorax; C, dorsal view of carapace; D, frontal view of cephalothorax; E, outer view of right chela.

Fig. 28. Arcotheres similis (Bürger, 1895), ovigerous female (9.3 × 7.8 mm) (ZRC 2017.1034), Changi, Singapore. A, overall dorsal view; B, ventral view of cephalothorax; C, dorsal view of carapace; D, frontal view of cephalothorax.

Fig. 30. Arcotheres similis (Bürger, 1895). A–K, ovigerous female (9.3 × 7.8 mm) (ZRC 2017.1034), Singapore; L, ovigerous female (6.7 × 5.5 mm) (NHM 1936.6.19.2), Singapore (holotype of Pinnotheres spinidactylus Gordon, 1936). A–D, left P2–P5, respectively; D’, distal part of dactylus of left P5 showing stiff subdistal spinules (subventral view, soft setae omitted); E–H, right P2–P5, respectively; H’, L, distal part of dactylus of right P5 showing stiff subdistal spinules (subventral view, soft setae omitted); I, outer view of left chela and carpus; J, outer view of left MXP3 (setae omitted); K, posterior margin of epistome. Scales = A–H, I, 1.0 mm; J, K, 0.5 mm; D’, H’ = 0.25 mm; L = 0.10 mm.

Fig. 31. Arcotheres similis (Bürger, 1895). A–C, male (5.5 × 5.8 mm) (ZRC 2017.1264), Singapore; D, male (3.3 × 3.3 mm) (NHM 1936.6.19.3), Singapore (paratype of Pinnotheres spinidactylus Gordon, 1936). A, D, overall dorsal view; B, frontal view of cephalothorax; C, outer view of right chela.

Fig. 32. Arcotheres similis (Bürger, 1895), male (5.5 × 5.8 mm) (ZRC 2017.1264), Singapore. A, dorsal view of carapace; B, pleon (setae omitted); C, left MXP3 (setae denuded); D–G, left P2–P5, respectively (setae omitted); H–K, right P2–P5, respectively; G’, distal part of dactylus of left P5 showing stiff subdistal spinules (dorsal view, soft setae omitted); K’, distal part of dactylus of right P5 showing stiff subdistal spinules (dorsal view, soft setae omitted); L, left G1 (ventral view); M, N, left G1 (dorsal view, setae omitted); O, left G2. Scales = A, D–K, 1.0 mm; B, C, L–O, 0.5 mm; G’, K’, 0.25 mm.

Fig. 33. Arcotheres similis (Bürger, 1895). A, B, ovigerous female (6.7 × 5.5 mm) (NHM 1936.6.19.2), Singapore (holotype of Pinnotheres spinidactylus Gordon, 1936); C, holotype female (8.3 × 6.4 mm) (SMF-ZMG 956 Go 950a), Philippines (holotype of Pinnotheres similis Bürger, 1895); D, female (7.3 × 6.0 mm; soft) (ZRC 1965.11.24.47), Sarawak; E, F, male (3.3 × 3.3 mm) (NHM 1936.6.19.3), Singapore; G–I, male (4.8 × 5.0 mm) (NHM 1936.6.19.14), Singapore; J, K, male (5.7 × 5.6 mm) (ZRC 2019.1026), Lombok, Indonesia; L, male (3.3 × 3.3 mm) (NHM 1936.6.19.3), Singapore (paratype of P. spinidactylus Gordon, 1936). A, left MXP3 (inner view); B, palp of left MXP3 (outer view); C, D, right MXP3 (outer view); E, G, J, left G1 (ventral view); F, distal part of left G1 (ventral view); H, K, distal part of left G1 (dorsal view); I, left G2; L, male pleonal somites 5, 6 and telson. A, B, E, F, after Gordon (1936: figs. 1c, 2a); C, after Ahyong & Ng (2007: fig. 14C). Scales = D, G–K, 0.5 mm; L, 0.2 mm.

Fig. 5. Arcotheres palaensis (Bürger, 1895). A, B, lectotype female (10.2 × 8.4 mm) (SMF-ZMG 948a), Palau. A, overall dorsal view; B, ventral view of cephalothorax.

Fig. 6. Arcotheres palaensis (Bürger, 1895). A, B, female (5.3 × 4.7 mm) (SMF-ZMG 172a) (lectotype of Pinnotheres arcophilus Bürger, 1895), Philippines; C–F, ovigerous female (5.1 × 4.3 mm) (ZRC 1999.1202), Indonesia. A, C, overall dorsal view; B, D, dorsal view of carapace; E, frontal view of cephalothorax; F, outer view of right chela.

Fig. 4. Arcotheres palaensis (Bürger, 1895), ovigerous female (11.6 × 10.3 mm) (ZRC 2020.11), Peninsular Malaysia, colour in life. Two subventral views showing eyes, antennules, antennae, and MXP3.

Fig. 13. Arcotheres palaensis (Bürger, 1895), dorsal view of carapace. A, ovigerous female (13.3 × 11.2 mm) (ZRC 2017.1281), Peninsular Malaysia; B, female (8.9 × 6.5 mm) (ZRC 1965.11.24.27), Singapore; C, ovigerous female (8.5 × 7.2 mm) (ZRC 1992.8378), Peninsular Malaysia; D, female (9.3 × 8.3 mm) (ZRC 2020.1), Peninsular Malaysia; E, ovigerous female (8.7 × 8.0 mm) (ZRC 2020.1), Peninsular Malaysia; F, ovigerous female (7.1× 5.7 mm) (ZRC 1993.120), Peninsular Malaysia; G, female (7.7 × 6.2 mm) (ZRC 1993.121), Indonesia; H, female (8.8 × 7.8 mm) (ZRC 2018.764), Lombok, Indonesia.

Fig. 22. Arcotheres palaensis (Bürger, 1895). A–N, male (3.6 × 3.6 mm) (ZRC 2019.1788), Indonesia; O, male (2.8 × 2.5 mm) (SMF- ZMG 172b) (paralectotype of Pinnotheres arcophilus Bürger, 1895), Philippines. A, left MXP3; B–E, left P2–P5, respectively; F–I, right P2–P5, respectively; J, pleon; K, left G1 (ventral view); L, M, left G1 (slightly different dorsal views); N, left G2; O, pleonal somites 3–5, telson, and left G1. Scales = A, K–N, 0.2 mm; B–J, 0.5 mm; O, 0.1 mm.

Fig. 40. Arcotheres exiguus (Bürger, 1895), female (6.8 × 4.8 mm) (CAS), China (holotype of Pinnotheres obscuridentata Dai & Song, 1986); after Dai & Song (1986: text-fig. 3). A, overall dorsal view; B, left MXP3; C, outer view of right chela; D–G, right P2–P5 dactyli. Scales = A, 2.0 mm; B–G, 0.5 mm.