Eusphalerum kanti Shavrin & Yamamoto

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 kanti Shavrin & Yamamoto sp. nov. Figures 3, 4, 21-23, 24-29, 30-33, 34-44

Type materials examined.

Holotype (male) and paratype (female), FMNHINS-3260630, complete specimens as inclusions in a piece of dark yellow to reddish orange Baltic amber, 21.6 mm × 12.7 mm × 6.3 mm in size (Figs 3, 4), with the following labels: "SYAC 0027 | Baltic | prob. Anthobium" <rectangular small label, handwritten>, "07[printed] 09 [handwritten] | Baltic / Dominican | Larva/Adult ( × 2) [printed] [handwritten] |? Anthobium [handwritten] | Axel Niggeloh | Schalksmuehle" <large rectangular label, printed>, "15[printed]01[handwritten] - SYAC 00[printed] 27[handwritten] | Baltic / Burmite | Other: | Larva / Adult | prob. Anthobium [handwritten] | 2 in amber [handwritten] | Baltic Sea coast [handwritten] | Shûhei Yamamoto’s | Amber Collection" <large rectangular label, printed>, "[FMNH barcode at left side of label] FMNHINS | 3965993 | FIELD MUSEUM | AMBER" <small rectangular label, printed>, "HOLOTYPE | Eusphalerum | kanti sp. nov. | Shavrin A. & Yamamoto S. des. 2019" <red rectangular label, printed>, "PARATYPE | Eusphalerum | kanti sp. nov. | Shavrin A. & Yamamoto S. des. 2018" <red rectangular label, printed> (FMNH).

Preservation.

The holotype is best observed on its dorsal side, close to the surface of the amber piece and with apical part of the body somewhat deeper (Fig. 3): head, pronotum and basal portion of elytra are visible from the lateral edge of the amber. The paratype is oriented dorsolaterally and located close to the outer surface of the amber piece (Fig. 3). Syninclusion: imago of Diptera about 2.00 mm length, including wings.

Locality and horizon.

Baltic amber from Baltic Sea Coast, further details unknown; mid-Eocene (ca 44 Ma; Wappler 2005).

Description.

Measurements (n = 2): HW (holotype): 0.47; HL (holotype): 0.33; OL (paratype): 0.18; AL (paratype): 0.75; PML × PMW (III, IV): III: 0.05 × 0.02, IV: 0.11 × 0.02; PL (holotype): 0.42; PW: 0.77; ESL (paratype): 1.25; EW (paratype): 1.15; MTbL (paratype): 0.42; MTrL (paratype): 0.24 ( I–IV: 0.12; V: 0.12); AW:?; TL: 2.60 (holotype)-2.70 (paratype). Antennomeres with lengths × widths (paratype): 1: 0.12 × 0.04; 2: 0.06 × 0.02; 3: 0.07 × 0.02; 4: 0.06 × 0.02; 5-6: 0.06 × 0.03; 7: 0.05 × 0.04; 8: 0.05 × 0.05; 9-10: 0.05 × 0.06; 11: 0.12 × 0.06.

Body elongate, convex (Figs 21, 24, 34, 37); body laterally as in Figure 36; body dorsolaterally as in Figure 23; body ventrally as in Figures 22, 25, 35. The specimens appear black, with mouthparts, antennae and legs yellow-brown; tarsi and basal portion of apical maxillary palpomere yellow. Body glossy and glabrous, without visible setation; antennomeres with elongate setae (Fig. 28).

Head about 1.4 times as wide as long (Figs 29, 39); middle portion of head slightly flattened, without visible grooves in front of ocelli, median impressions and occipital line; postocular carina smooth and indistinct. Head laterally as in Figure 42 and dorsolaterally as in Figure 28. Head with moderately irregular, dense and small punctation, markedly denser on posterior portion; middle part of neck with sparse small punctures (Fig. 43); infraorbital ridges with indistinct diagonal small meshes between punctures. Eyes large, widely convex (Figs 35, 37). Ocelli large, situated at level of posterior margins of eyes (Figs 28, 37), distance between ocelli distinctly longer than distance between ocellus and posterior margin of eye. Apical segment of maxillary palpi elongate, twice as long as preceding segment, about same width in middle as preceding segment, from middle gradually narrowed apicad (Figs 22-23, 28). Gular sutures with rounded apical parts, widely separated from each other (Figs 35, 38). Antenna (Figs 21-23, 25, 28, 29) moderately long, slightly exceeding shoulders of elytra, with elongate setae; basal antennomere wide and oblong, antennomere 2 slightly swollen and elongate, antennomere 3 thin and long, antennomere 4 slightly wider than antennomere 3, antennomeres 5 and 6 twice as long as wide, antennomeres 7 and 8 slightly and antennomeres 9 and 10 distinctly transverse, apical antennomere twice as long as wide, strongly narrowed in apical third toward acute apex.

Pronotum slightly convex, moderately short and transverse, 1.8 times as wide as long, 1.6 times as wide as head, widest at about middle, distinctly more narrowed posterad than anterad (Figs 21, 24, 37); apical margin straight, distinctly narrower than posterior margin; anterior angles widely rounded and distinctly protruded anterad (Figs 39, 43); posterior angles widely rounded; lateral margins distinctly emarginate, without crenulation on lateral edges (Figs 37, 39); pronotum with moderately widely elevated middle portion (Fig. 37), with very indistinct small transverse impression in mediobasal third; lateral portions narrowly but distinctly explanate, each with distinct moderately deep semioval impression at middle (Fig. 39). Pronotum with irregular small punctation like that on head but slightly deeper, markedly sparser in mediobasal and lateral portions; median portion with very indistinct transverse microsculpture. Prosternum with moderately wide intercoxal process (Figs 25, 26, 35, 38). Mesoventrite with thin, elongate and acute intercoxal process indistinctly reaching apical third of mesocoxae (Figs 35, 41). Scutellum large and wide, with several very small punctures in basal portion (Figs 21, 23, 24). Metaventrite convex (Fig. 36), with wide and deep metacoxal cavities and moderately wide metaventral process, reaching middle of mesocoxae, not contacting with apex of mesosternal process (Figs 25, 35, 41). Median part of prosternum and metaventrite with moderately dense small punctation (Figs 25, 35).

Elytra sexually dimorphic (male: Figs 30, 31; female: Figs 32, 33), distinctly longer than wide (Figs 21, 23, 24, 34) and more convex behind middle; in lateral view (Fig. 36) very long, about three times as long as pronotum, distinctly widened apicad from middle, reaching middle of abdominal tergite VI, with widely rounded apical angles (Fig. 40). Punctation of elytra larger and significantly denser than that on pronotum, markedly smaller on parascutellar portion and along suture, sparser on apical portion, larger and coarser in lateroapical and medioapical portions (Figs 21, 23, 24, 31, 33).

Legs with relatively wide femora (Figs 22, 23, 25, 26, 35, 36), tibiae thin, gradually widened apicad, about as long as femora, covered by elongate setae, markedly stronger on lateral margin (Figs 22, 23, 29, 36, 44); tarsomeres 1-4 with dense distinctly elongate setae ventrally; apical metatarsomere long, as long as previous tarsomeres together (excluding tarsal claws) (Figs 23, 27-29, 36).

Abdomen distinctly narrower than elytra (Figs 27, 40); apical margin of tergite VII with indistinct brick-wall sculpture; abdominal tergites with sparse small punctures and no visible microsculpture (Fig. 27); sternites VII and VIII of both males and females without modifications (Fig. 44).

Male. Elytra as in Figure 24; apical margin of elytra widely rounded (Figs 30, 31). Apical margin of abdominal tergite VIII somewhat straight. Apical margin of abdominal sternite VIII widely rounded (Fig. 27).

Female. Elytra as in Figure 21; apical margin of elytra distinctly prolonged at sutural apex (Figs 32, 33). Apical margin of abdominal tergite VIII and sternite VIII (Figs 27, 40) straight. Genital segment with markedly elongate gonocoxites and very small styli (Figs 27, 40).

Etymology.

Patronymic, the species is named in honour of the great German philosopher Immanuel Kant (1724-1804), the author of the doctrine of transcendental idealism.

Remarks.

The paratype of Eu. kanti sp. nov. was visualised three-dimensionally using a micro-CT scan. Although the result was not very satisfactory, we could observe the fossil from multiple additional angles (Figs 34, 44). Based on this scan, we could describe more characters that were not visible with light microscopy. The fossil was assigned to the tribe Eusphalerini and genus Eusphalerum based on the general shape of the body, shapes and length of short and slightly widened tarsomeres 1-4, with dense and elongate ventral setae, together about as long as apical tarsomere, and shape of the elytra of female slightly longer than that of male, with prolonged portion at sutural apex (Figs 32, 33). This floricolous genus contains 260 valid species ( Zanetti 2014) distributed in the Holarctic Region. Earlier, the genus was subdivided into two subgenera: Eusphalerum and Pareusphalerum Coiffait, 1959 ( Zanetti 1987), but because several species of sensu stricto and Pareusphalerum were overlapping in some morphological characters, the latter was synonymized with the nominotypical taxon ( Tronquet and Zanetti 2008). Based on general morphological features of the aedeagus, female accessory sclerite and, in some cases, shapes of the modified apical abdominal sternites, several species groups have been erected for many species of the genus (e.g. Zanetti 1987, 1993, 2014). However, to date, this diverse genus remains insufficiently studied globally and is in need of further phylogenetic revision because of unclear relations between both species groups and the tribe Eusphalerini with related Omaliini .

The new species is difficult to compare with extant species as they typically differ from each other by the morphology of the aedeagus and female genital structures. However, based on the shape of the strongly elongate and dimorphic elytra, Eu. kanti sp. nov. is like members of the following species groups: North American convexum ( Zanetti 2014; four species distributed in Canada and USA) and western Palaearctic amplipenne ( Zanetti 1993; one species known from Turkey), longipenne ( Zanetti 1987; six species distributed in Middle and South Europe), montivagum ( Zanetti 1987, 1992, 1993, 2004, 2012a; 10 species distributed in Central and Southern Europe and Turkey) and anale ( Tronquet and Zanetti 2001; three species from the central-western part of Europe). The new species differs from the convexum group by the presence of the postocular carina, by the dorsal portion of head without visible impressions, by the shape of the apical tarsomere slightly longer than that in species of convexum group and by the abdominal sternite VII of male without modifications. It differs from the amplipenne group by its somewhat smaller and darker body, sparser punctation of the forebody and shape of metatarsus of male, slightly curved in Eu. amplipenne (see Zanetti 1993: fig. 13). The new species shares similar length of the body and postocular carina with some species of the longipenne group, but differs by the darker body and longer apical tarsomeres. Based on the dark body, general characters of punctation and microsculpture of head and pronotum, Eu. kanti sp. nov. is somewhat like some species of the montivagum and anale groups, for example Southern European Eu. schatzmayri (Koch, 1938), Eu. anale (Erichson, 1840), Eu. brandmayri (Zanetti, 1981), and Eu. coiffaiti Nicolas, 1974, but it differs by the larger body (body length of members of the montivagum and anale groups varies from 1.50 to 2.50 mm) and more transverse pronotum. From all these groups, Eu. kanti sp. nov. differs by the absence of distinct grooves in front of the ocelli and elongate antennomeres 2-4 (Fig. 28).