Pycnomerus prebblei, Porch, Nick & Smith, Tessa R., 2017

Porch, Nick & Smith, Tessa R., 2017, New Pycnomerus Erichson (Coleoptera: Zopheridae: Pycnomerini) from Rimatara, French Polynesia, Zootaxa 4237 (1), pp. 154-166 : 162-164

Pycnomerus prebblei sp. nov.

(Fig.2,5)

Type material. Holotype: French Polynesia, Austral archipelago, Rimatara , Maunutu Swamp, MATO 2008 core, 430–435 cm depth—prothorax only . BPBM, Honolulu.

Paratype: French Polynesia, Austral archipelago, Rimatara , Maunutu Swamp, MATO 2008 core, 355–360 cm depth—prothorax only. Porch research collection.

Diagnosis. Distinguished from P. rimatara by the characters mentioned in the diagnosis for that species.

Description. Colour: Dark piceous-black.

Prothorax slightly longer than wide, the greatest width at about 1/4 of pronotal length. Lateral margins almost straight and moderately parallel, slightly converging behind widest point until strongly rounded posterior angles, weakly crenulate with shallow and very narrow marginal sulcus adjacent to narrow, raised border. Both specimens exhibit an extremely slight but noticeable sinuation to side margins at about, or just behind, middle. Anterior angles obtuse angulate and distinctly produced by sinuation of anterior marginal border. Anterior margin almost straight in middle 3/4 and unbordered until it joins the lateral margins. Posterior angles strongly rounded with small denticles interrupting. Posterior margin very weakly lobed and evenly rounded, completely margined by sulcus, a continuation of the lateral sulcus. A pair of narrow, shallow, fovae in basal sulcus which is evenly rounded between. Basal border narrow, not obviously punctate.

Pronotal disk flat over medial third, a little declivous to anterior margin, and strongly declivous to lateral margins and anterior and posterior angles. Disk lacking medial impressions and bearing relatively evenly sized and evenly distributed punctures except at middle where density is reduced. Punctures small, elongate oval, separated by 1-3 times their length, distinctly elongate longitudinally, their long axis orientated slightly medially and with curvature of disk elsewhere. Microsculpture of pronotal disk reduced-weak, pronotal interstices appearing shiny.

Prosternum moderately punctate with punctures usually separated by their length or more. Anterior edge with weakly developed margin that extends only across middle third and a very weak sulcus, a distinct row of small punctures. Apex of prosternal process truncate to very broadly rounded, the latter potentially a preservational artefact of the paratype.

Physical dimensions. Based on measurement of 2 types. Measurements of Holotype in parentheses. Pronotum length: (0.75)– 0.83 mm. Pronotum width: (0.71)– 0.80 mm. Anterior width of pronotum: (0.59)–0.65) mm. Medial width of pronotum: (0.705)– 0.785 mm. Base of pronotum: (0.62)– 0.64 mm. Lateral length of pronotum: (0.61)– 0.71 mm. Length/Width ratio: 1.04–(1.06).

Etymology. This species is named for friend and colleague Mat Prebble who was instrumental in the initial discovery of the existence of the wonderful fossil records from the Austral archipelago and who collected (with Porch) the sedimentary material from which the specimens described here were recovered.

Associated (Non-type) material. French Polynesia, Austral archipelago, Rimatara , Maunutu Swamp, MATO 2008 core, 305–310 cm depth, 1 male head: on the basis of size, microsculpture and differences from heads known to be P. rimatara likely to belong to P. prebblei ; ditto, except 310–315 cm depth, articulated elytra: on the basis of size, microsculpture and differences from elytra considered to belong to P. rimatara , these elytra are likely those of P. prebblei ; ditto, except 390–395 cm depth, 1 complete left elytron. All in Porch.

Description of male head considered to belong to P. prebblei : width in front of eyes about equal to temporal width, distinctly parallel immediately in front of eyes for half of eye length. Frontal margins concavely bisinuate and narrowed (at approx. 40o angle) to anterior margin, itself distinctly concave with right margin further produced than left. Shallow depression of coalescing punctures on each side of frons, and (barely) in front of eyes. Head shining with punctures separated by several times their diameter, less abundant adjacent to and anterior of, eye. Eye moderately coarsely facetted, about 7–10 ommatidia in length along lateral margin, dorsally, and similar size ventrally. Male with setose pit on submentum.

Head measurements and ratios: Clypeus width: 0.49 mm. Interocular width (dorsal): 0.42 mm. Temporal width: 0.48 mm. Eye length (dorsal): 0.11 mm. Eye length (ventral): 0.12 mm. Ratio eye length dorsally/Eye length ventrally: 0.91. Ratio interocular width dorsally/interocular width ventrally: 1.00.

Description of elytra considered to belong to P. prebblei : subparallel, widest immediately in front of basal third, evenly and very slightly curved to rounded humerus with several very weak dentae. Evenly curved to apex. Elytral intervals 1-5 mostly wider than striae, becoming narrower from interval 5. Intervals shiny, apparently lacking microsculpture and lacking punctures. Striae with short ‘oxhide ingot’ punctures slightly longer than wide in discal striae, separated by their length or greater. Elytron length (1.83–1.92 mm). Elytron width (0.40 mm; only one specimen measured due to deformation).

Distribution. Like Pycnomerus rimatara , known only from Rimatara and likely to be a Rimatara endemic. Similarly, considered potentially extinct: material known from other Austral Archipelago islands (Tubuai, Raivavae and Rapa) and nearby Cook Islands (Mangaia and Atiu) represent different taxa.

Habitus reconstructions. Given that we have what we consider to be the principal sclerites of both Rimataran Pycnomerus species described here, we have reconstructed the suggested habitus of each using size matched sclerites ( Figure 6 ). For P. rimatara this involved the use of a single right elytron image (specimen from C1T2 100–105cm), reflected for reproduction as a left elytron, and the articulated head and prothorax of the holotype. For P. prebblei this necessitated the use of three isolated sclerites, the holotype prothorax, an unassociated head, and unassociated, articulated elytra. The reconstructions give our best estimate of the habitus of the two newly described species.

Figures

FIGURE 6. Proposed reconstructions of Pycnomerus rimatara (left) and P. prebblei (right). Reconstructions are based on holotype head and pronotum and a single reflected, non-type, elytron for P. rimatara and holotype prothorax and non-type head and articulated elytra for P. prebblei. Scale bar = 1 mm.