Nicobium necrocrator, Alekseev & Háva & Pankowski & Bukejs, 2024

Alekseev, Vitalii, Háva, Jiří, Pankowski, Madeline V. & Bukejs, Andris, 2024, First record of Nicobium LeConte (Coleoptera: Ptinidae: Anobiinae) from Baltic amber with the description of a new extinct species, Zootaxa 5496 (1), pp. 133-139 : 134-136

Nicobium necrocrator sp. nov.

( Figs 1–5 )

Type material. Holotype: No. KAM 8656 [KRAM]; “* Holotype / Nicobium / necrocrator sp. nov. /Alekseev, Háva, / Pankowski et Bukejs / des. 2024” [red handwritten label]; adult, sex unknown; prothorax is insufficiently visible due to legs position and gas bubbles on left side of inclusion. A complete beetle is included in a transparent, yellow, irregularly shaped amber piece with dimensions of 15× 14 mm and a maximum thickness of 14 mm, preserved without supplementary fixation. Syninclusions: a few small stellate Fagaceae trichomes.

Type stratum. Baltic amber from Eocene amber-bearing Blaue Erde deposits; estimated age: middle–late Eocene.

Type locality. Yantarny settlement (formerly Palmnicken), Sambian (Samland) Peninsula, Kaliningrad Region, Russia .

Description. Measurements: body length (from anterior margin of pronotum to elytral apex along midline) 4.0 mm, body maximum width across both elytra 2.0 mm; head length (including mandible) 0.86 mm, head maximum width across eyes 1.13 mm; pronotal length 1.25 mm, pronotal maximum width 1.5 mm; elytral length 2.75 mm, elytral maximum width 2.0 mm.

Body shape elongate, subcylindrical; body color entirely dark brown, with appendages rufous. Dorsum with inconspicuous, semi-erect, fine, sparse pubescence; legs with shorter and denser pubescence; ventral surface of thorax apparently glabrous; abdominal ventrites with short pubescence.

Head hypognathous, evenly convex; vertex with small granules, interspaces between granules about as wide as diameter of one granule; frons glabrous, with sparse, very fine punctures. Compound eyes large, oval, convex, entire, finely facetted, without ommatidial setae; distance between compound eyes nearly equal to 1.2× vertical diameter of one eye. Mandibles flat, robust, inner surface tridentate with apical tooth longest. Last labial palpomere triangular with widened apex, anterior margin tridentate. Antennal insertions widely separated by distance of 1.3× vertical diameter of one eye. Antennae with 11 antennomeres, with loose 3-segmented club, extending to basal onesixth of elytron; relative length ratios of antennomeres 1–11 equal to 15-10-6-5-5-5-5-5-25-25-30. Scape elongateoval; pedicel elongate, conical, 3.0× as long as wide; antennomere 3 conical, slightly longer than subsequent antennomere; antennomeres 4–8 subequal in size and shape, conical, elongate, slightly longer than wide, dilated apically; antennomere 9 and 10 subequal in shape and size, flattened, widened distally; antennomere 11 longest, elongate, narrowly spindle-shaped, pointed.

Pronotum convex medially, with bump in middle, narrower than elytra at base, transverse, 1.2× as wide as long, with maximum width in anterior one-third; lateral sides and posterior edge flattened. Pronotal granulation larger, coarser, and denser than granulation on head, denser at base and medially; distance between granules about equal to 0.5–1.0× diameter of one granule. Pronotal pubescence fine, erect, with setae inconspicuous on disc and longer laterally and at anterior edge. Posterior pronotal angles distinct, rectangular, sharp; anterior angles protruding, forming short lobes, slightly upturned, flattened, rectangular, sharp. Anterior pronotal edge margined, rounded medially; posterior edge margined, widely rounded along entire length; lateral edges concave at base, rounded anteriad, finely serrate.

Scutellar shield triangular, with rounded angles, as long as wide. Elytra subparallel, elongate, about 1.4× longer than wide, moderately convex, with well-developed humeri. Elytral punctation dense, moderately large, arranged in striae; striae distinct throughout entire length of elytron; elytral strial punctures elongate, rectangular with rounded angles medially, more rounded and smaller posteriad and laterad; interstrial intervals flat; distance between striae narrower at base and wider apicad, about 1.0–2.0× as wide as one strial puncture. Shortened scutellar stria present, consisting of five punctures. Elytral pubescence fine, semierect, discernible only on lateral sides. Epipleura glabrous, with sparse granulation; wide near humeri and gradually narrowing postriad, but not reaching elytral apex. Metaventrite with disc convex, not excavate anteriorly; covered with rather dense granulation; discrimen distinct in posterior one-third.

Legs rather short and moderately robust. Mesocoxae globose, separated by 1.3× transverse diameter of mesocoxa; metacoxae elongate, transverse, separated by one length of metacoxa. Trochanters subglobose. Femora and tibiae nearly equal in length; femora weakly thickened; tibiae straight, not widened apically. Tarsal formula: 5-5-5. Tarsomere 1 longer than tarsomere 2 or 3 (first metatarsomere 1.25× as long as second metatarsomere); tarsomeres 2 and 3 subequal in length; tarsomere 4 widened apically, lobed; tarsomere 5 rather short, triangular, about as long as tarsomere 4. Tarsal claws about 0.5× as long as tarsomere 5; swollen, without tooth basally.

Abdomen with five visible ventrites covered with fine and short pubescence; ventrite 5 rounded apically. Relative length ratios of ventrites 1–5 equal to 10:16:15:8:18 (measured medially).

Differential diagnosis. Nicobium necrocrator sp. nov. differs from all extant congeners in the combination of the following characters: (1) elytral pubescence sparse and inconspicuous, not forming a pattern or even uniform cover on the disc (in contrast to double pubescence on dorsum of N. zuzartei Bercedo et Arnáiz, 2007 ; to uniformly pubescent elytra on N. castaneum (Olivier, 1790) ; to elytral pubescence arranged in transverse bands on N. hirtum (Illiger, 1807)) ; (2) posterior pronotal angles rectangular and sharp, and pronotal lateral sides concave at base (in contrast to widely rounded pronotal posterior angles in N. gorbatovskyi Toskina, 2014 and to evenly rounded lateral edges of pronotum in N. schneideri Reitter, 1878 ); (3) mesocoxae separated by distance equal to 1.3× their transverse diameter (in contrast to mesocoxae separated by distance equal to 0.5× coxal diameter in N. hirtum and to mesocoxae separated by distance less than 0.5× coxal diameter in N. gorbatovskyi ); (4) elytral interstrial intervals flat (in contrast to convex interstrial intervals in N. hirtum and N. schneideri ); elytra about 1.4× longer than wide (in contrast to elytra 1.6–1.8× longer than wide in N. castaneum ); and (5) elytral strial punctures elongate (in contrast to rounded strial punctures in N. castaneum and N. schneideri ).

The newly described extinct species, Nicobium necrocrator sp. nov., can be distinguished from the Mesozoic congener Nicobium cretaceum Háva et Zahradník, 2023 in the granulate pronotum (in contrast to a punctate pronotum in N. cretaceum ), larger body size (2.1 mm in N. cretaceum ), pronotal bump without furrow (furrow present in N. cretaceum ), antennomere 11 the longest (antennomere 11 not longer than antennomere 10 in N. cretaceum ), and abdominal ventrites of different lengths (in contrast to all ventrites of equal length in N. cretaceum ).

The new species can be easily distinguished from all other Ptinidae described from Baltic amber by the combination of genus-level differences mentioned in the paragraph “taxonomic assignment” as well as its comparatively large body size (4 mm), wide subparallel elytra with developed humeri, and regularly striate-punctate elytra. Nicobium necrocrator sp. nov. resembles representatives of the genus Trichodesma with its four coeval species known from Baltic amber and keyed in Bukejs et al. (2018). The newly described species, however, differs from these taxa in the tarsal claws without basal tooth, distinct posterior pronotal angles, a less-developed convex pronotal bump, and the elytra and pronotum without tufts of erect setae.

Derivatio nominis. The specific epithet necrocrator is derived from Ancient Greek νεκρός (dead body) and κράτος (power), meaning “dead lord.” The name is used as a noun in apposition.

Figures

FIGURES 1–2. Nicobium necrocrator sp. nov., holotype, No. KAM 8656 [KRAM]: 1: Habitus, dorsal view; 2: Habitus, ventral view. Scale bars = 1.0 mm.

FIGURES 3–5. Nicobium necrocrator sp. nov., holotype, No. KAM 8656 [KRAM]: 3: Habitus, left lateral view; 4: Habitus, frontal view; 5: Habitus, caudal view. Scale bars = 1.0 mm.