Arcotheres ocularius Komai, Kawai & Ng, 2020

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 : 168-171

Arcotheres ocularius Komai, Kawai & Ng, 2020

( Figs. 23 , 24 )

Arcotheres ocularius Komai, Kawai & Ng, 2020: 232 , figs. 7–17 [type locality: Fiji]; De Gier & Becker, 2020: tab. 1.

Type material. Holotype: ovigerous female (11.8 × 10.2 mm) ( CBM-ZC 15952), Kumi Village, Viti Levu, Fiji, 17°53.21′S, 178°36.07′E, intertidal, with Anadara sp. ( Bivalvia: Arcidae ), 16 August 2010, coll. K. Kawai. Paratypes: 1 female (8.9 × 8.2 mm), 3 ovigerous females (9.6 × 8.4 mm, 10.9 × 9.7 mm, 12.3 × 11.9 mm) ( ZRC 2019.1877), coll. 16 August 2010; 2 females (5.5 × 5.0 mm, 6.9 × 6.4 mm), 17 ovigerous females (8.5 × 7.4–13.4 × 9.6 mm) ( CBM-ZC 15953), coll. 16 August 2010; 1 male (6.2 × 6.8 mm) ( CBM-ZC 15954); 1 female (5.2 × 5.2 mm) ( CBM-ZC 15956), coll. 16 August 2010; 1 male (4.6 × 5.0 mm) ( CBM-ZC 15957), coll. 16 August 2010; 2 males (3.2 × 3.2 mm, 3.3 × 3.4 mm) ( CBMZC 15958), coll. 16 August 2010; 1 male (5.8 × 5.8 mm) ( CBM-ZC 15959); 1 male (4.8 × 5.4 mm) ( ZRC 2020.7), coll. 16 August 2010; 1 ovigerous female (10.7 × 9.1 mm) ( CBM-ZC 15960), coll. 6 September 2011; 7 ovigerous females (8.6 × 7.2–10.7 × 9.5 mm) ( CBM-ZC 15961), August 2018; 5 ovigerous females (9.4 × 8.0–10.7 × 9.3 mm) ( ZRC 2020.8), August 2018 (all from same locality as holotype); 1 ovigerous female ( CBM-ZC 19562), Ucikumi, near Kumi Village, coll. 22 February 2019.

Other material examined. Fiji: 4 poorly preserved females (4.2 × 3.3–6.0 × 4.6 mm) ( ZRC 2019.1878), intertidal, associated with Anadara sp. , coll. K. Kawai, August 2018. Indonesia: 1 female (9.4 × 8.4 mm) ( ZRC 2019.1025), Teluk Kodek, Lombok, intertidal, in Anadara antiquata (Linnaeus, 1758) (Arcidae) , coll. S. Dwiono, 12 November 2013.

Description. Carapace and pereopods well chitinised. Female: Carapace subcircular, wider than long; dorsal and lateral surfaces smooth, glabrous; appearing domed in frontal view; front projecting anteriorly beyond orbits, margin gently convex to almost straight; anterolateral margin smooth, subparallel with frontal margin or gently sloping posteriorly, forming rounded angle with posterolateral margin ( Fig. 23 ). Eyes clearly visible in dorsal view in adults; mobile, filling orbit ( Fig. 23 ). Epistome with median part low, triangular, lateral margins wide, gently concave ( Komai et al., 2020: figs. 7D, 8B).

MXP3 outer surface with scattered short setae; ischiomerus completely fused, subrhomboidal, inner margin rounded to gently angular at widest point; carpus short; propodus about 3 times as long as high, subspatulate, longer than carpus, tip rounded; dactylus digitiform, inserted submedially on flexor margin of propodus, tip reaching end of or slightly overreaching propodal apex; exopod relatively slender, about two-thirds length of ischiomerus, flagellum 2-segmented ( Fig. 24A, B ).

Chela short, stout, dactylus about two-thirds palm length; palm relatively slender, medially widest; outer surfaces of palm, fingers (except for distal part) almost glabrous, with only scattered short setae; ventral margin of palm gently convex, with low bulge near midlength; dactylus occlusal margin with 1 subproximal tooth; pollex occlusal margin with 1 low sharp proximal tooth and denticles; tips of fingers sharp, hooked ( Fig. 24C ).

P2–P5 dorsally, ventrally unarmed; outer surface covered with scattered, very short setae or glabrous; ventral margins of propodus and dactylus slightly more setose; merus relatively short, stout, relative lengths of meri P4>P3>P2>P5; left (sometimes right) P4 distinctly the longer; P2 and P3 dactyli short, subequal, tip gently hooked, half length of propodus; longer P4 dactylus elongate, almost straight, sparsely setose, longer than P5 dactylus; P5 merus 4.1–4.4 times longer than wide; P5 dactylus shorter than longer P5 dactylus, longer than shorter P4 dactylus, margins lined with short and long setae, denser on ventral margin, distoflexor margin without rows of spinules ( Fig. 24D–K ).

Pleon extending to buccal region, covering bases of P2–P5; telson gently recessed into concave distal margin of somite 6 ( Komai et al., 2020: fig. 8D, E).

Male: Carapace almost circular, slightly longer than wide; dorsal surface almost smooth, gently inflated, lateral surfaces with setae; front projecting anteriorly, margin gently convex to sinuous ( Komai et al., 2020: figs. 12, 13A, 15A). Eyes distinctly visible in dorsal view ( Komai et al., 2020: figs. 12, 13A, 15A). MXP3 as in female except dactylus just reaching tip of propodus ( Komai et al., 2020: figs. 13C, 16A). 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 ( Komai et al., 2020: figs. 13D, 15B). Chela relatively stout, shorter than in female ( Komai et al., 2020: figs. 14A, 16B). P2–P5 dorsally, ventrally unarmed; outer surface covered with short setae; P3 and P4 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 P4 dactylus slightly longer, more slender than right side; P4 and P5 dactylus subequal to that of P3, covered with short setae ( Komai et al., 2020: figs. 14C–G, 15A, 16D–H). Pleon slender, triangular, widest at somite 3, lateral margins of somite 4 gently sinuous to almost straight; somite 6 subtrapezoidal; telson subhexagonal, much wider than long ( Komai et al., 2020: figs. 13D, H, 15F). G1 relatively stout, arcuate, curved outwards, tip subtruncate, without elongate process ( Komai et al., 2020: figs. 13I, J, 15G, H). G2 short, with spatuliform tip; exopod slightly longer than endopod ( Komai et al., 2020: figs. 13K, 15I).

Variation. Komai et al. (2020: 241) noted that the carapace shape varied from broadly ovate ( Komai et al., 2020: fig. 7A) to almost circular ( Komai et al., 2020: fig. 7B, C). The condition of the dorsally exposed eyes and dactylus reaching end of or slightly overreaching MXP3 propodus, however, were always reliable.

Colour. “Entirely whitish; female ovary, visible through integument, orange; cornea of eye red” ( Komai et al., 2020: 241).

Host. Known from Anadara sp. in Fiji and Anadara antiquata (Linnaeus, 1758) in Lombok ( Arcidae Lamarck, 1809 ).

Remarks. Komai et al. (2020) discussed the taxonomy of A. ocularius at length, differentiating it from the morphologically similar A. palaensis s. str. in the more strongly chitinised carapace and pereopods, eyes that are clearly visible in dorsal view in adult females, the prominently projecting front, the MXP3 dactylus being always long and reaching or overreaching the propodus apex, the male telson being subpentagonal or subhexagonal, and the G1 with a subtruncate tip ( Figs. 23 , 24A, B ; Komai et al., 2020: figs. 7A–D, 8C, F, G, 10B, E, 13D, H–J, 15F–H, 16A). They also noted that unpublished genetic studies by Tsang Ling Ming from the Chinese University of Hong Kong show both species to be distinct. Arcotheres ocularius is known from Fiji and Lombok, Indonesia, but not recorded from the main Sunda Shelf where A. palaensis is common. Both species, however, are present in Lombok.

Komai et al. (2020: 244) observed that in the figure of the lectotype of A. arcophilus in Ahyong & Ng (2007b: fig. 2A) (present Figs. 6A , 19A ), the “female P4 merus is proportionately longer in A. ocularius ” than in A. arcophilus . We have re-examined the lectotype of A. arcophilus (at present synonymised under A. palaensis ) and the P4 merus is actually similar to A. ocularius and more like the condition in a more recent female of A. palaensis from Indonesia ( Figs. 6C , 19E–L ). In the protruding front and dorsally visible eyes in adult females, A. ocularius resembles some specimens of A. palaensis , but the carapace of A. ocularius is always more strongly chitinised, the MXP3 dactylus always long and overreaching the propodus apex, the longer female P4 merus relatively longer, the male telson subpentagonal or subhexagonal, and the G1 with a subtruncate tip ( Figs. 23 , 24A, B ; Komai et al., 2020: figs. 7A–D, 8C, F, G, 10B, E, 13D, H–J, 15F–H, 16A).

Distribution. Western Pacific, from Fiji to southeastern Indonesia.

Figures

Fig. 23. Arcotheres ocularius Komai, Kawai & Ng, 2020, overall dorsal view. A, paratype ovigerous female (10.9 × 9.7 mm) (ZRC 2019.1877), Fiji; B, female (9.4 × 8.4 mm) (ZRC 2019.1025), Indonesia.

Fig. 24. Arcotheres ocularius Komai, Kawai & Ng, 2020. A, C–K, paratype female (10.9 × 9.7 mm) (ZRC 2019.1877), Fiji; B, female (9.4 × 8.4 mm) (ZRC 2019.1025), Indonesia. A, B, left MXP3; C, outer view of right chela; D–G, left P2–P5, respectively; H–K, right P2–P5, respectively. Scales = A, B, 0.5 mm; C–K, 1.0 mm.

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. 19. Arcotheres palaensis (Bürger, 1895). A–C, female (5.3 × 4.7 mm) (SMF-ZMG 172a) (lectotype of Pinnotheres arcophilus Bürger, 1895), Ubay, Philippines; D–M ovigerous female (5.1 × 4.3 mm) (ZRC 1999.1202), Indonesia. A, overall dorsal view; B, right MXP3; C, right chela; D, left MXP3; E–H, left P2–P5, respectively; I–L, right P2–P5, respectively; M, frontal margin of carapace showing eyes in dorsal view. Scales = A–L, 0.5 mm; M, 1.0 mm.