Arcotheres rayi Ahyong & Ng, 2007b

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 : 194-199

publication ID	https://doi.org/ 10.26107/RBZ-2022-0009
publication LSID	lsid:zoobank.org:pub:BE6164AE-1C24-4E01-8B7B-D80764F147B3
persistent identifier	https://treatment.plazi.org/id/03E887D8-CE4D-FF90-34F8-1A40D5A37651
treatment provided by	Felipe
scientific name	Arcotheres rayi Ahyong & Ng, 2007b
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Arcotheres rayi Ahyong & Ng, 2007b View in CoL

( Figs. 46–49 View Fig View Fig View Fig View Fig , 50H–L View Fig , 51 View Fig , 52 View Fig )

Arcotheres rayi Ahyong & Ng, 2007b: 203 View in CoL , fig. 11 [type locality: Mariveles or Bohol, Philippines]; Ng et al., 2008: 248; Clark & Schram, 2009: 450; Ng et al., 2017: 1094; Trivedi et al., 2018a: 54, 56; Trivedi et al., 2019: 590, tab. 1; De Gier & Becker, 2020: tab. 1.

Type material. Holotype: female (11.3 × 8.7 mm) ( SMFZMG952 ), Mariveles or Bohol, Philippines, coll. Semper (paralectotype of Xenophthalmus latifrons Bürger, 1895 ).

Other material examined. Peninsular Malaysia: 3 males (4.2 × 3.8–4.4 × 4.0 mm), 8 ovigerous females (5.4 × 5.1–8.4 × 7.0 mm), 5 spent females (5.6 × 4.0–6.9 × 5.2 mm) , 10 females with bopyrids (5.4 × 3.8–10.4 × 6.2 mm) ( ZRC 2013.1416 View Materials ), Bentong market, Pahang, in Paphia sp. , coll. M. Low, 10 May 2010 .

Description. Female: Carapace and pereopods poorly chitinised, soft. Carapace subcircular to subhexagonal, wider than long; dorsal and lateral surfaces smooth, glabrous; appearing domed in frontal view; front in line with (larger specimens) or slightly produced anteriorly (smaller specimens) beyond transverse anterolateral margins, margin gently convex; anterior margin with (larger specimens) or without (smaller specimens) shallow notch above orbit flanking front ( Figs. 46A View Fig , 47A, C, D View Fig , 48A–C View Fig , 49A View Fig ). Eyes small, not or just visible in dorsal view in adults; mobile, completely filling orbit ( Figs. 46A View Fig , 47A, C, D View Fig , 48A–C View Fig , 49A, C View Fig ). Epistome with median part triangular, lateral margins gently concave ( Fig. 49C View Fig ).

MXP3 outer surface with scattered short setae; ischiomerus completely fused, subrhomboidal, inner margin usually rounded, at widest point; carpus short; propodus about 3 times as long as high, subspatulate, distinctly longer than carpus, tip rounded to subtruncate; dactylus slender, inserted medially on propodus, tip underreaching or just reaching propodal apex; exopod relatively slender, about two-thirds length of ischiomerus, flagellum 2-segmented ( Fig. 49B View Fig ).

Chela not prominently elongate, dactylus half to two-thirds palm length; palm relatively slender, proximally narrower than distally; outer surfaces of palm, fingers (except for distal part) almost glabrous, with only scattered short setae; ventral margin of palm gently convex to sinuous; dactylus occlusal margin with distinct subproximal tooth; pollex occlusal margin usually with 1 low proximal tooth (sometimes obsolete), 1 submedian tooth, and minute denticles; tips of fingers sharp, hooked ( Figs. 46C View Fig , 47E View Fig , 49E View Fig ).

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 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; P4 longer dactylus elongate, weakly falciform, distinctly longer than half propodus length, longer than P5 dactylus; P5 merus 3.9–4.5 times longer than wide; P5 dactylus shorter than propodus extensor margin, longer than P2 and P3 dactyli, length/height <5.0, margins lined with short and long setae, denser on ventral margin, distoflexor margin without rows of spinules ( Figs. 49F–M View Fig , 50H–L View Fig ).

Pleon extending to buccal region, covering bases of P2–P5; telson gently recessed into concave distal margin of somite 6 ( Figs. 46B View Fig , 47B View Fig , 49D View Fig ).

Male: Carapace and pereopods well chitinised, firm. Carapace almost circular, slightly wider than long; dorsal surface almost smooth, not prominently inflated, lateral surfaces with setae; front projecting anteriorly, margin gently sinuous to almost straight ( Figs. 51A View Fig , 52A View Fig ). MXP3 as in female but dactylus shorter ( Fig. 52B View Fig ). 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. Chela relatively stout, shorter than in female ( Figs. 51C View Fig , 52D View Fig ). 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; right P4 dactylus slightly longer, more slender than left side; P4 and P5 dactylus subequal to that of P3, covered with short setae ( Fig. 52E–L View Fig ). Pleon slender, triangular, widest at somite 3, lateral margins of somite 4 gently concave; somite 6 trapezoidal; telson semicircular, wider than long ( Fig. 52M View Fig ). G1 relatively stout, arcuate, curved outwards, with short triangular subdistal dorsal projection, tip rounded ( Fig. 52N, O View Fig ). G2 short, with spatuliform tip; exopod about two-thirds endopod length ( Fig. 52P View Fig ).

Variation. The carapace shape varies somewhat, the most important being the prominence of the front, whose variation is broadly size-related. In the holotype of A. rayi , the largest known specimen of the species, the front does not protrude in advance of the general anterior margin, but is demarcated on either side by a shallow notch above each orbit ( Fig. 46 View Fig ). Other specimens, however, have a front that protrudes anteriorly beyond the general anterior margin, some retaining the notch on either side of the front ( Fig. 48B, C View Fig ), but most others without ( Figs. 47 View Fig , 48A View Fig , 49 View Fig ). The length of the longer P5 dactylus varies allometrically, being proportionately shorter in small specimens ( Table 2; Fig. 50H–L View Fig ).

Host. Known only from Paphia sp. ( Veneridae Rafinesque, 1815 ).

Remarks. Arcotheres rayi is morphologically very close to A. exiguus , but the good series of specimens has permitted evaluation of intraspecific variability, enabling more reliable recognition of interspecific differences. Females of A. rayi , in which the carapace front is demarcated by a notch in the anterior margin above each orbit ( Figs. 46 View Fig , 48B, C, E View Fig ), are readily distinguished from A. exiguus , which does not have the anterior carapace notches ( Figs. 33B, C View Fig , 35B, E View Fig ,