Pycnomerus mahanatoa, Porch & Smith & Greig, 2020

Porch, Nick, Smith, Tessa R. & Greig, Kelly, 2020, Five new Pycnomerus Erichson (Coleoptera: Zopheridae: Pycnomerini) from Raivavae, French Polynesia, Zootaxa 4718 (2), pp. 239-250 : 246-247

Pycnomerus mahanatoa sp. nov. Porch & Greig

( Fig. 1 )

Type Locality: Raʹirua Swamp, 0.8 km E. of Raʹirua, at 23°52.115’S 147°40.718’W.

Type material. Holotype: French Polynesia, Austral archipelago, Raivavae, Raʹirua Swamp, DA 4 2008 core, 205–210 cm depth—incomplete prothorax only, missing about left 1/3 of pronotum and small part of hypomeron. BPBM, Honolulu.

Diagnosis. Although represented by a single incomplete specimen, we describe this species because it is very distinctly different from the other Raivavae Pycnomerus species. Distinguished from co-occurring species and those from Rimatara ( Porch & Smith 2017) and Tubuai (Greig & Porch, unpubl. data) by its combination of small size, elongate shape, wide anterior angles (wider than basal angles), and steeply declivous lateral margins.

Description. Based on single incomplete holotype.

Colour: Black.

Prothorax distinctly longer than estimated width, with greatest width at about 1/5–1/4 of pronotal length. Lateral margins very sparsely and indistinctly crenulate, arcuate anteriorly and relatively straight from just behind widest point to hind angle. Marginal sulcus narrow, wider than very narrow lateral margin. Anterior angles rounded and not produced. Anterior border without margin and moderately arcuate laterally, to straight in middle. Posterior angles obtuse. Posterior margin narrowly arcuate and sparsely punctate. Basal sulcus same width as basal border, continuous across base and a little interrupted by discal punctures laterally. Pronotal disk strongly punctate, punctures crater-like, circular to slightly longitudinally ovate, separated by half to several times their length. Punctures closer posteriorly and on lateral margins where they begin to coalesce. Surface between punctures moderately shining. Short pale yellow setae occasionally preserved in punctures.

Prosternum with circular to laterally elongate punctures separated by one to two times their length except on prosternal process where they are adjacent. Prosternal process arcuate emarginate. Hypomera very sparsely punctate.

Physical dimensions and Ratios.

Pronotum measurements based on incomplete holotype. Some measurements based on extrapolation from half prothorax width. Pronotum length: 0.64 mm. Estimated pronotum width: 0.54. Estimated anterior width of pronotum: 0.46. Estimated medial width of pronotum: 0.50. Estimated width of base of pronotum: 0.44. Lateral length of pronotum: 0.53 mm. Estimated Length/Width ratio: 1.19.

Prosternum measurements based on incomplete holotype. Prosternum length: 0.42 mm. Length prosternum in front of coxae: 0.26 mm. Anterior foramen: 0.37 mm. Prosternal process intercoxal width: 0.16 mm. Estimated maximum prosternal process width: 0.23 mm. Ratio of Prosternal length/Length in front of coxae: 1.62.

Distribution. Known only from Raʹirua swamp, Raivavae, and likely to be a Raivavae endemic. Potentially ex- tinct: material known from other Austral Archipelago islands (Tubuai, Raivavae and Rapa) and nearby Cook Islands (Mangaia and Atiu) represent different taxa.

Etymology. Named for the Mahanatoa region of Raivavae, close to where the species was found in the sediments of the swamp we refer to here as Raʹirua swamp.

Figures

FIGURE 1. Holotypes. Pycnomerus raivavae articulated prothorax and head, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, RAI16-2 2016 cores, 150–200 cm depth). Pycnomerus rairua prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, DA4 cores, 180–185 cm depth). Pycnomerus vavitu prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua Swamp, DA4 2008 core, 170–175 cm depth). Pycnomerus mahanatoa prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua Swamp, DA4 2008 core, 205–210 cm depth). Pycnomerus taralewisae prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, DA4 cores, 245–250 cm depth). Scale bars = 0.5 mm