Eusphalerum sp. 1

Shavrin, Alexey V. & Yamamoto, Shuhei, 2019, Unexpected palaeodiversity of omaliine rove beetles in Eocene Baltic amber (Coleoptera, Staphylinidae, Omaliinae), ZooKeys 863, pp. 35-83 : 35

Eusphalerum sp. 1 Figures 14-16, 73-75, 76-80

Materials examined.

2 males (no. 6, no. 9), 2 females (no. 3, no. 7), 5 unsexed specimens (no. 1, no. 2, no. 4, no. 5, no. 8), FMNHINS-3260631, complete specimens as inclusions in yellow Baltic amber 31.3 mm × 20.6 mm × 12.6 mm in size (Figs 14-16), with the following labels: "15[printed]03[handwritten]-SYAC 00[printed]8[handwritten] | Baltic / Burmite | Other: | Larva / Adult | Omaliinae 11 exs, [handwritten] | Baltic Sea Coast [handwritten] | Axel (Germany) [handwritten] | Shûhei Yamamoto’s | Amber Collection" <large rectangular label, printed>, "Axel Niggeloh" <rectangular label, printed>, "[FMNH barcode at left side of label] FMNHINS | 3260631 | AMBER [handwritten] | FIELD MUSEUM | Wet" <small rectangular label, printed>, "Eusphalerum | sp. 1 | Shavrin A.V. det. 2018" <rectangular label, printed> (FMNH).

Preservation.

The specimens are visible from one surface of the piece of amber (specimens were numbered as in Figs 14-16). One of the best preserved specimens (male, no. 6) is located dorsolaterally: the surface of the body, left antenna, and part of the abdomen in lateral view are clearly visible. Eight other specimens are present with differing degrees of visible details. A male (no. 9) is located deep in the piece of amber at the level of its median convexity; its pronotum, elytra, and abdomen are clearly visible dorsolaterally, and the antennae, mouthparts, legs and parts of the thoracic segments and abdomen are visible ventrally. A female (no. 3) is laterally oriented close to the outer surface of the amber piece; its basal antennomeres of the right antenna are partly visible, and the mouthparts, including maxillary and labial palpi, lateral side of the elytra, and partly thoracic sclerites, and legs relatively are visible. Another female (no. 7) is located laterally deep in the piece of amber and, therefore, the dorsal side of its body is visible but strongly cloudy and distorted; details of the structure of maxillary palpus, right antenna, five legs partly, some details of the thorax and abdomen, including apical portion with the genital segment are more or less visible from lateral view. An unsexed specimen (no. 1) is located dorsally near the outer surface of the piece of amber; only the pronotum and elytra are partly visible. Another unsexed specimen (no. 2) is located dorsally near the outer surface of the piece of amber near specimen no. 1; the apical segments of its right antenna, pronotum, and elytra are clearly visible. An unsexed specimen (no. 4) is located a little deeper in the piece of amber, close to specimen no. 3; its hind wings are extended and cover the entire abdomen. The body is not clearly visible except for the pronotum and elytra. An unsexed specimen (no. 5) is located dorsally near specimen no. 6, with the left antenna, posterior portion of head, pronotum, and elytra partially visible. Another unsexed specimen (no. 8) is located deep in the piece of amber, near specimen no. 9, and has its hind wings extended so as to cover the dorsal side of the abdomen; there is a milky covering on the lateral side of the body, and, therefore, the middle and hind legs are only partly visible in lateral view and the pronotum and elytra are partly visible in dorsal view. Syninclusion near outer surface of the piece of amber close to its margin: imago of Diptera about 2.80 mm length, including wings (Fig. 14).

Description.

Measurements (n = 9): HW: 0.67 (no. 5); HL:?; OL: 0.18 (no. 6); AL (no. 6): 0.74; PML × PMW:?; PL: 0.41-0.46; PW: 0.87 (no. 5); ESL: 0.83-0.96; EW: 0.71-0.77; MTbL (no. 8): 0.40; MTrL (no. 8): 0.28; AW: 0.68-0.74; TL: ~2.50-3.20. Antennomeres with lengths × widths (no. 6): 1: 0.15 × 0.05; 2: 0.08 × 0.04; 3: 0.06 × 0.03; 4-6: 0.05 × 0.03; 7: 0.05 × 0.04; 8: 0.06 × 0.04; 9 0.05 × 0.05; 10: 0.06 × 0.05; 11: 0.08 × 0.05.

Body moderately wide, convex (Figs 73-76). Body laterally as in Figures 77 and 79, dorsally as in Figs 73, 74, and 76 and dorsolaterally as in Figure 78. The specimens appear brown to black. Body glabrous, without visible setation.

Head transverse, with slightly convex middle portion, without grooves in front of ocelli (Fig. 75); punctation of posterior portion of head irregular, small, and sparse; surface between punctures with relatively large transverse fine microsculpture, distinctly larger and coarser on neck. Eyes large, widely convex (Figs 75, 77). Ocelli relatively small, slightly convex (Figs 73, 75). Apical segment of maxillary palp elongate, slightly narrower and distinctly longer than penultimate segment, from middle gradually narrowed apicad, with moderately acute apex (Fig. 77). Antenna reaching basal margin of elytra; basal antennomere markedly wide, antennomere 2 swollen and slightly elongate, 3 with thin basal portion, slightly widened apicad, antennomeres 4-6 slightly shorter than 3, 7 slightly wider than 6 and 8, 10 slightly transverse in apical portion, apical antennomere wider than penultimate segment, from apical third gradually narrowed apicad (Figs 73, 75, 78, 79).

Pronotum slightly convex and distinctly transverse, about twice as wide as long, distinctly broader than head, widest in middle, more narrowed posterad than anterad; apical margin slightly rounded, about as broad as posterior margin, anterior (Fig. 75) and posterior angles (Fig. 80) widely rounded; laterobasal margins slightly concave; lateral margins in middle narrowly marginate; median disc of pronotum with very indistinct transverse and laterobasal portions with indistinct wide impressions (Figs 73-76, 80). Pronotum with more or less regular small and sparse punctation, sometimes with wide impunctate longitudinal area on disc, with distinct and moderately large transverse and diagonal microsculpture (Figs 73-76, 80). Scutellum without visible punctures, with distinct isodiametric microsculpture (Figs 73, 74, 76, 80).

Elytra slightly convex, distinctly longer than broad, twice as long as pronotum, from middle slightly widened apicad, reaching apical margin of abdominal tergite IV, with widely rounded apical angles and straight apical margin truncated at suture (Figs 73-76, 78). Punctation markedly denser and deeper than that on pronotum, smaller on basal and apical margins and near scutellum; microsculpture as that on pronotum (Figs 73, 74, 76, 78).

Abdomen slightly narrower than elytra, with small, moderately sparse punctation and fine indistinct microsculpture.

Male. Apical margin of abdominal tergite VIII rounded. Apical margin of abdominal sternite VIII slightly sinuate.

Female. Details of shapes of apical abdominal segment not visible.

Remarks.

The present unique piece of amber contains an interesting and rare aggregation of omaliine specimens which apparently belong to one species. Based on the shape of the body and other structures (antennae, maxillary palpus), features of punctation and microsculpture, etc., the species belongs to Eusphalerini or Omaliini . Tarsi of fore- and middle legs are partly visible in one specimen (Fig. 77); tarsi of this specimen has long and indistinctly dense setae on lateral portions of tarsomeres 1-4 that are common in species of the genus Eusphalerum . Based on the shape of the body and other morphological details, and lack of additional morphological data, we have not found similar species among extant representatives of the genus, so we here treat this taxon as Eusphalerum sp. 1. We did not observe sexual dimorphism in the shape of apical portions of the elytra, which often occurs in Eusphalerum , as was observed for Eu. kanti sp. nov. above. Furthermore, the morphology of the aedeagus should be studied, as species of the genus are reliably distinguished by the shapes of the median lobe of the aedeagus and the parameres.