Plenotheres coarctatus ( Bürger, 1895 ) Ng & Ahyong, 2022

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 : 216-223

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-CE23-FF88-3417-1B12D5D7786F
treatment provided by	Felipe
scientific name	Plenotheres coarctatus ( Bürger, 1895 )
status	comb. nov.

Treatment

Plenotheres coarctatus ( Bürger, 1895) View in CoL , new combination

( Figs. 63–68 View Fig View Fig View Fig View Fig View Fig View Fig )

Pinnotheres coarctatus Bürger, 1895: 369 View in CoL , pl. 9 fig. 7, pl. 10 fig. 7 [type locality: Tipoeka, Timika, Indonesian Papua, Indonesia, by present neotype designation]; Tesch, 1918: 248 (list); Estampador, 1937: 546 (list); Silas & Alagarswami, 1967: 1197 (list); Serène, 1968: 93; Schmitt et al., 1973: 42.

Pinnoteres coarctatus — Balss, 1957: 1419 (list).

Arcotheres coarctatus View in CoL — Ahyong & Ng, 2007b: 195, fig. 3A; Ng et al., 2008: 248; Ng et al., 2017: 1094; Trivedi et al., 2018a: 197; De Gier & Becker, 2020: tab. 1; Ahyong & Ng, 2021: 207–209, fig. 17.

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

Type material. Neotype (here designated): female (13.1 × 11.4 mm) ( ZRC 2020.13 View Materials ), Tipoeka, Timika, Indonesian Papua, Indonesia, in Polymesoda expansa , coll. D. L. Rahayu et al., 26 April 2000.

Other material examined. Indonesia: 2 males (2.7 × 2.8 mm, 3.3 × 3.4 mm) , 1 female (11.9 × 10.8 mm), 2 juvenile females (3.4 × 3.3 mm, 3.2 × 3.2 mm) ( ZRC 2018.765 View Materials ), same data as neotype ; 1 female (7.9 × 7.2 mm) ( ZRC 2019.1789 View Materials ), in Glauconome rugosa , from Kandang Kerbau market, Singapore, from Indonesia , coll. P. K. L. Ng, 29 December 2019 ; 2 females (11.3 × 10.7 mm, 10.2 × 9.5 mm) ( ZRC 2017.1284 View Materials ), Ajkwa, Timika Province, Indonesian Papua, no host data, coll. D. L. Rahayu et al., 20 January 2000 ; 1 female (11.3 × 10.2 mm) ( ZRC 2017.1285 View Materials ), Ajkwa, Timika Province, Indonesian Papua, in Geloina coaxans , coll. D. L. Rahayu et al., 11 January 2000 ; 1 female (13.2 × 11.6 mm) ( ZRC 2017.1286 View Materials ), Tipoeka, Timika Province, Indonesian Papua, in Polymesoda expansa , coll. D. L. Rahayu et al., 21 December 1999 ; 2 females (11.5 × 10.7 mm, 6.7 × 6.1 mm) ( ZRC 2018.766 View Materials ), in Batissa violacea , peat site, Timika, Indonesian Papua, Indonesia , coll. D. L. Rahayu et al., 27 November 1999 . Singapore: 1 female (14.1 × 13.1 mm) ( ZRC 2001.2237 View Materials ), Loyang mangroves, off Loyang Avenue , in Polymesoda expansa , coll. N. Sivasothi, 17–18 July 2001 ; 3 females (16.5 × 14.4 mm, 15.5 × 13.2 mm, 13.9 × 12.4 mm) ( ZRC 2003.681 View Materials ), in “ Geloina zeylanica (Lamarck, 1806) ” (= present Geloina coaxans ), coll. A. Ibrahim, June 2003 ; 2 females (14.4 × 13.2 mm, 13.3 × 11.9 mm) ( ZRC 2012.1223 View Materials ), in Polymesoda expansa , mudflats, Pulau Ubin, coll. G. Jahvel, 5 November 2012 . Peninsular Malaysia: 1 female (10.1 × 9.1 mm) ( ZRC 1995.438 View Materials ), in Glauconome rugosa , from market, coll. P. K. L. Ng, 21 December 1992 ; 5 females (11.7 × 11.2 mm, 9.5 × 8.8 mm, 9.4 × 9.0 mm, 8.7 × 8.2 mm, 6.6 × 6.3 mm) ( ZRC 2017.1283 View Materials ), in Glauconome rugosa , from Chinatown market, Singapore, from Malaysia, coll. P. K. L. Ng, 21 January 2018 ; 9 ovigerous females (6.8 × 6.5 mm, 8.0 × 7.1 mm, 8.1 × 6.7 mm, 8.1 × 7.6 mm, 8.4 × 8.6 mm, 9.0 × 8.0 mm, 9.1 × 8.0 mm, 9.9 × 8.8 mm, 10.5 × 9.2 mm) ( ZRC 2018.246 View Materials ), 2 ovigerous females (9.1 × 8.4 mm, 7.2 × 6.1 mm) ( AM P105903 ), in Glauconome rugosa, Chinatown market, Singapore, from Malaysia, coll. P. K. L. Ng, 11 February 2018 ; 4 females (8.0 × 7.6 mm, 9.1 × 8.0 mm, 10.2 × 9.5 mm, 11.9 × 10.6 mm) ( ZRC 2018.254 View Materials ), in Glauconome rugosa, Chinatown market, Singapore , from Malaysia, coll. P. K. L. Ng, 11 March 2018 ; 3 females (photographed 8.4 × 7.9 mm) ( ZRC 2020.10 View Materials ), in Glauconome rugosa , from Kandang Kerbau market, Singapore , coll. P. K. L. Ng, 29 March 2020 . Thailand: 1 ovigerous female (8.8 × 7.6 mm) ( NHMD Cr-284250), Lem Ngob, Gulf of Thailand , mangrove swamp, coll. Th. Mortensen, 23–27 December 1900 . Description. Carapace and pereopods poorly chitinised. Female: Carapace subcircular, slightly wider than long; appearing domed in frontal view; dorsal and lateral surfaces smooth, glabrous; with pair of fine longitudinally arcuate grooves almost always well defined, extending from behind orbits to indistinct gastrocardiac groove; front slightly projecting anteriorly beyond anterolateral margins, margin straight to gently convex; anterolateral margin smooth, convex, gently curving to join rounded angle with posterolateral margin ( Figs. 63D View Fig , 64A View Fig , 65 View Fig ). Eyes small, just visible in dorsal view in adults; mobile, filling orbit ( Figs. 63D–F View Fig , 64A, C View Fig ). Epistome with median part triangular, lateral margins concave ( Fig. 64C View Fig ) .

MXP3 outer surface with scattered short setae; ischiomerus completely fused, subrhomboidal, inner margin prominently angular (almost 90°) at widest point; carpus short; propodus conical, about 2.5 times as long as high, distinctly longer than carpus, tip rounded; dactylus slender, inserted at proximal one-third of propodus, tip slightly overreaching propodal apex; exopod relatively stout, with proximal part very wide, about two-thirds length of ischiomerus, flagellum 2-segmented ( Figs. 64C View Fig , 66I View Fig ).

Chela not prominently elongate, stout, dactylus exceeding two-thirds palm length; palm 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 almost straight; dactylus occlusal margin with blunt triangular tooth proximal to midlength, margin straight in distal half, finely denticulate, sparsely setose; pollex occlusal margin with 2 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 to inner surface of palm ( Fig. 64D View Fig ).

P2–P5 dorsally, ventrally unarmed; margins of P2 and P3 covered with short setae; outer surface of P3 (especially merus) with dense long setae; ventral margins of dactylus with long dense setae; merus relatively longer, more slender, relative lengths of meri P4>P3>P2>P5; right (sometimes left) P4 merus and propodus distinctly the longer; P2–P4 dactyli relatively short, subequal, tip hooked, shorter than half propodus length; dactylus of longer P4 stout, weakly curved, longer than P2 and P3 dactylus, shorter than P5 dactylus; P5 merus 4.3–4.4 times longer than wide; P5 dactylus longest, gently falciform, ventral margin lined with short and long setae, distoflexor margin with relatively short row of 6–12 small spinules ( Fig. 66A–K View Fig ).

Pleon extending to buccal region, covering bases of P2–P5; telson slightly recessed into concave distal margin of somite 6 ( Fig. 64B View Fig ).

Male: Carapace almost circular, slightly longer than wide; dorsal surface smooth, inflated, lateral surfaces with setae; front projecting anteriorly, margin almost straight ( Fig. 67A, B View Fig ). Eyes distinctly visible in dorsal view ( Fig. 67A, B View Fig ). MXP3 as in female but dactylus shorter than propodus ( Fig. 68J–L 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. 67C View Fig , 68I 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 P3=P4>P2>P5; dactyli of P2–P4 progressively longer; left P4 merus slightly longer than right side; P4 and P5 dactylus subequal to that of P3, covered with short setae ( Fig. 68A–H View Fig ). Pleon triangular, widest at somite 3, lateral margins of somite 4 gently concave; somite 6 subrectangular; telson semicircular, slightly wider than long ( Fig. 68M View Fig ). G1 relatively stout, widely C-shaped, curved outwards, with elongate sharp subdistal dorsal flap at right angles to main structure ( Fig. 68N–P View Fig ). G2 short, with spatuliform tip; exopod long, curved ( Fig. 68Q View Fig ).

Variation. General setation is often less dense in larger specimens. The gastric grooves on the carapace are usually distinct, but less obvious in a few specimens, probably as a result of poor preservation. The single row of spinules on the ventral margin of the distal part of the P5 dactylus varies in number from 6 to 12, but the proximal ones are frequently very low and barely visible ( Fig. 66J, K View Fig ).

Colour. In life, the carapace varies from brown and grey to dirty white overall, with the ovaries appearing purplish and the eyes dull red ( Fig. 63 View Fig ).

Host. Confirmed from Geloina coaxans (Gmelin, 1791) , Polymesoda expansa (Mousson, 1849) , and Batissa violacea (Lamarck, 1818) ( Cyrenidae Gray, 1840 ); or Glauconome rugosa Hanley, 1843 ( Glauconomidae Gray, 1853 ). Both families are in the superfamily Cyrenoidea Gray, 1840 . Bürger (1895) recorded the host as “Cahebe” (= Polymesoda spp. ) ( Schmitt et al., 1973). Note that Bürger’s (1895) “Cahebe” is probably a misspelling of the local name for a commonly harvested brackish water clam ( Geloina sp. ), known as “kabibe” in Tagalog and other Philippine languages, or “cabebe” or “cabibe” under old Hispanised renderings (J. C. E. Mendoza, pers. comm.; Ahyong & Ng, 2021).

Remarks. Ahyong & Ng (2007b: 195) regarded Plenotheres coarctatus , new combination, originally described from Zamboanga, Philippines, and whose original types are lost, to be sufficiently recognisable as to not require a neotype designation at that time. Females of Pl. coarctatus as understood here are distinguishable from species of Arcotheres by the pair of anterior dorsal carapace grooves. Males of Pl. coarctatus , however, closely resemble male A. exiguus and A. rayi in most respects including the gonopod and P5 structure; they can be externally distinguished by the shape and elongation of the MXP3 propodus, which is shorter and conical in Pl. coarctatus , with the dactylus articulating slightly proximal to the midlength ( Fig. 68J–L View Fig ) (versus elongate and spatulate with the dactylus articulating slightly distal to the midlength in the two species of Arcotheres ; Figs. 44A View Fig , 45A View Fig , 52B View Fig ). In view of the strong similarities between males of A. exiguus , A. rayi , and what is here considered to be Pl. coarctatus ; and because this species is herein made the type species of a new genus, a neotype selection is required to fix its identity. This will stabilise the taxonomy of Pinnotheres coarctatus and the genus. The neotype selected is a female (13.1 × 11.4 mm; ZRC 2020.13) collected from Polymesoda expansa in Indonesian Papua. This location is southeast of the original type locality in southern Philippines.