Clambus helheimricus sp. nov. (Figs 1–3) Type material. Holotype No. 1470-2 [CCHH], adult, sex unknown, complete beetle, included in small-sized yellow amber piece embedded in a block of GTS polyester resin with approximate side-length dimensions of 13 × 10 × 5 mm. The specimen is clearly visible in lateral aspect. Syninclusions are represented by one ant specimens (? Lasius sp.), three specimens of Acari, the head of an insect (? aphid) and minute particles of detritus. Type strata. Baltic amber, Upper or mid-Eocene. Type locality. Yantarny settlement (formerly Palmnicken), Sambian (Samland) Peninsula, Kaliningrad Region, Russia. Etymology. The specific epithet “ helheimricus ” is formed after the word Helheimr (Helheim, or Hel)—“concealed place, the underworld”—realm of the dead, existing beneath one of the three roots of the world ash-tree Yggdrasil and ruled by the goddess Hel in the old Scandinavian mythology. Differential diagnosis. Clambus helheimricus sp. nov. differs from extant species of the genus in the following combination of characters: dorsal surface apparently bare, impunctate, and shiny; temporal angles rounded, situated behind posterior margin of eyes; eyes relatively small, longitudinally oval; metaventrite and coxal plates pubescent, not shagreened; posterior horizontal plate of metaventrite moderately reduced in middle, approximately 3× shorter medially than laterally; metacoxal plates sparsely punctate; abdominal ventrites 2–5 pubescent, finely and densely punctate. Description. Habitus. Body length 1.01 mm; maximum width 0.78 mm; rounded, conglobate; convex, smooth, impunctate and shiny dorsally. Body dark brown, legs rufous. Head. Hypognathous, transverse (approximately 1.4× as wide as long), convex, widest across temporal angles behind eyes, narrower than pronotum. Clypeal margin arcuate, with sparse short setation. Eyes from dorsal view relatively small, longitudinally oval, very finely facetted, consisting of approximately 50 facets. Interfacetal setae absent. Lateral margin of eye diverging from temporal margin. Temporal angles rounded, situated behind posterior margin of eyes. Antennal insertions exposed in dorsal view, widely separated. Antennae distinctly clubbed, relatively short (when posteriorly extended reaching middle of pronotum), consisting of 10 antennomeres. Scape and pedicel enlarged; antennomere 3 long and cylindrical; antennomeres 4–7 elongate; antennomere 8 rounded, as long as wide; antennomeres 9–10 distinctly enlarged and clubbed. Antennomere 9 the largest, triangular with rounded angles, slightly longer than broad. Ratio of antennomere lengths: 6.0: 4.0: 8.0: 4.0: 2.0: 2.0: 2.0: 3.0: 11.0: 5.0. Antennal club covered with long, thick, flexible, white hairs. Thorax. Pronotum transverse (in dorsal view about 0.41× as long as wide), convex. Lateral pronotal carina rounded. Anterior pronotal angles rectangular, rounded; posterior angles obtuse, broadly rounded. Posterior pronotal margin concave; anterior pronotal margin broadly arcuate. Scutellar shield triangular, as wide as long. Elytra strongly convex, rounded, almost as broad as pronotum basally, approximately 0.7× as long as their maximal combined width and 2.7× as long as pronotum. Elytral punctation or setation not apparent. Epipleura incomplete, narrow, present only anteriorly. Pro- and mesocoxal cavities open. Horizontal plate of metaventrite narrow in middle (approximately 0.3× as long as it lateral length), densely pubescent. Pubescence long, decumbent. Legs. Long and slender. Metaxocal plates large, covering metacoxae and abdominal ventrite 1, punctate, pubescent like horizontal plate of metaventrite. Punctation large, irregular; distance between punctures equal to 1.0–4.0× diameter of one puncture. Coxae cylindrical, projecting. Femora and tibiae slender. Tibiae pubescent. Tarsi tetramerous with tarsomeres simple, cylindrical, pubescent. Tarsomeres 1 and 4 long, almost equal in length; tarsomeres 2 and 3 shorter than tarsomeres 1 and 4. Claws simple, acute, symmetrical. Abdomen. With five ventrites. Ventrite 1 almost concealed by metacoxal plates; ratio of ventrite lengths 2–5: 2.0: 1.0: 1.0: 2.0. Ventrites 2–5 pubescent, finely and densely punctate. Distance between punctures equal to 0.8–1.0× diameter of one puncture. Ventrite 5 simple, without apparent long pubescence apically. Remark. Genitalia internal and obscured in this specimen. Metathoracic wings not visible. Assumed bionomy. Extant representatives of the genus Clambus are collected from decaying vegetation, leaf litter and rotten wood. Records indicate that the family is probably feeding on microfungi, though they may be found on Ascomycetes, Myxomycetes and Basidiomycetes, where they feed mainly on spores and hyphae (Leschen 2016). For the fossil species, a similar biology and relation with saproxylic environment and soil litter can be assumed.

Published as part of Alekseev, Vitalii I., 2017, A new species of minute beetle (Coleoptera: Clambidae) from Baltic amber (Paleogene, Eocene), pp. 141-145 in Zootaxa 4337 (1) on pages 142-143, DOI: 10.11646/zootaxa.4337.1.8, http://zenodo.org/record/1014111