Pycnomerus raivavae, 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 : 241-243

Pycnomerus raivavae sp. nov. Porch & Greig

( Fig.1 , 2 )

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, RAI 16-2 2016 cores, 150–200 cm depth—articulated head and prothorax, dorsally and ventrally complete except for appendages. BPBM, Honolulu.

Paratypes (8): French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, DA4 2008 core: 160–165 cm depth (1 prothorax) ; ditto except 180–185 cm depth (1 prothorax) ; ditto except 190–195 cm depth (1 prothorax) ; ditto except 240–245 cm depth (1 incomplete prothorax); Raivavae, Raʹirua swamp, RAI 16-2 2016 cores, 150–200 cm depth (4 prothoraces: 1 incomplete). BPBM, Honolulu and Porch research collection .

Diagnosis. Distinguished from co-occurring species and those from Rimatara ( Porch & Smith 2017) and Tubuai (Greig & Porch, unpubl. data) by its distinctive rounded shape, very sparse punctuation, largely effaced basal sulcus, and thickened, simple, pronotal margins.

Description. Based on holotype and 8 paratypes.

Colour: Dark piceous-black.

Prothorax approximately as wide as long, the greatest width at about 1/3—1/2 of pronotal length. Lateral margins arcuate and very weakly sinuate just before posterior angles. Lateral margin simple, with a marginal sulcus adjacent to a raised border, narrowest in middle and thickened anteriorly and especially posteriorly to hind angles. Anterior angles rounded and slightly produced. Anterior margin rounded to almost straight in middle, sinuate to anterior angles and unbordered. Posterior angles obtuse yet distinct. Posterior margin arcuate, with an almost effaced marginal channel, this depressed rather than sulcate and most well-developed inward of hind angles where it forms a small, shallow to moderately developed longitudinal fovea; in middle mostly effaced or as a slight transversely elongate depression. Basal border thick but indistinctly developed and with row of very small seta-bearing punctures. Pronotal disk elevated in front of middle, almost flat to weakly raised in medial third, declivous to all, especially lateral, margins. Disk not impressed. Punctures circular to mostly longitudinally ovate, separated by several to many times their length, bearing small, very pale yellowish setae (where preserved), shorter than puncture length. Punctures less abundant along middle, densest and most well developed laterally and more widely spaced posteriorly. Surface between punctures without obvious microsculpture, weakly to moderately shining.

Prosternum moderately punctate with rounded punctures usually separated by about their length or more, becoming closer and much smaller anteriorly and coalescing on hind margin of prosternal process. Medial punctures with distinct anteriorly-oriented, elongated emargination, becoming weaker away from middle. Anterior with weak impunctate margin that extends across much of prosternum, defined by an indistinct ridge in middle half, with a fringe of short pale yellow setae in well-preserved specimens. Prosternal process very wide (3 three times coxal width) and parallel to very slightly divergent adjacent to coxae, until abrupt postcoxal expansion.Apex of prosternal process weakly angulate emarginate to truncate. Hypomera moderately punctate.

Head (based on holotype specimen, head slightly pushed into prothorax). Almost completely impunctate anteriorly but weakly punctate behind antennal insertions. Eyes very small. Frontal margins weakly sinuate, narrowed and rounded to slightly medially protruded, anterior margin. Surface dull. Submentum densely punctured.

Physical dimensions and Ratios

Pronotum measurements based on 9 specimens. Measurements of Holotype in parentheses. Pronotum length: 0.68–0.89 (0.75) mm. Pronotum width: 0.64–0.90 (0.76) mm. Anterior width of pronotum: 0.49–0.66 (0.57) mm. Medial width of pronotum: 0.65–0.92 (0.76) mm. Base of pronotum: 0.56–0.82 (0.65) mm. Lateral length of pronotum: 0.57–0.80 (0.64) mm. Length/Width ratio: 0.96–1.05 (1.00).

Prosternum measurements based on 4 specimens. Prosternum length: 0.44–0.55 (0.48) mm. Length proster- num in front of coxae: 0.28–0.32 (0.29) mm. Anterior foramen: 0.44–0.53 (0.51) mm. Basal foramen: 0.44–0.54 (0.44) mm. Prosternal process intercoxal width: 0.23–0.29 (0.27) mm. Maximum prosternal process width: 0.27– 0.32 (0.32) mm. Ratio of Prosternal length/Length in front of coxae: 1.56–1.67 (1.66).

Head measurements based on holotype with head partly inside prothorax. Clypeus width: (0.46 mm). Interocular width (ventral): (est. 0.44 mm).

Associated (Non-type) material (sclerites other than prothorax or articulated head and prothorax). One distinctive elytral type almost certainly belongs to this species: it is the most common type, it is robust and wide and has similar sculpture to the prothorax: French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, DA4 2008 excavation, 170–175 cm depth—1 complete left elytron, 1 complete right elytron; ditto, except 165–170 cm depth, 1 complete left elytron, 1 complete right elytron ; ditto, except 140–145 cm depth, 1 incomplete right elytron ; ditto, except 190–195 cm depth, 1 complete right elytron ; ditto, except 150–155 cm depth, 1 incomplete right elytron. French Polynesia, Austral archipelago, Raivavae , Raʹirua swamp, RAI16.2 2016 excavation, 150–200 cm deptharticulated left and right elytra. Representative specimens in BPBM, Honolulu and Porch collection .

Distribution. Known only from Raʹirua swamp, Raivavae, and likely to be a Raivavae endemic. Subfossil and modern material from Tubuai and Rimatara does not include any material remotely close in appearance to this species. The fauna of nearby Rapa is poorly known, however the known modern collections and subfossil species present do not include this species. Potentially extinct.

Etymology. Named for its occurrence and apparent endemism on the island of Raivavae, French Polynesia.

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

FIGURE 2. Dorsal views of holotype and paratype prothoraces of P. raivavae; Holotype retains head indicated with ‘HT’. Scale bar = 0.5 mm.