Helioctamenus groehni Alekseev et Bukejs, 2024

ALEKSEEV, VITALII, MCKELLAR, RYAN C. & BUKEJS, ANDRIS, 2024, A revision and addition to Zopheridae (Coleoptera: Tenebrionoidea) in Baltic amber: possible connections between modern Holarctic distributions and Eocene ‘ amber forests’, Zootaxa 5536 (2), pp. 201-247 : 218-223

Helioctamenus groehni Alekseev et Bukejs sp. nov.

( Figs 17–26 )

Type material. Holotype: No. GPIH no. 5209 , CCGG no. 8706 (ex coll. Jonas Damzen JDC-12544 ); “Holotype / Helioctamenus groehni sp. nov. / Alekseev et Bukejs des. 2024” [red printed label]; adult, sex unknown. A complete beetle included in a transparent, yellow amber piece with dimensions of 20× 7 mm and a maximum thickness of 3 mm, preserved without supplementary fixation. Syninclusions: several stellate Fagaceae trichomes.

Paratype: No. GPIH no. 5217 , CCGG no. 8707 (ex coll. Jonas Damzen JDC-13157 ); “Paratype / Helioctamenus groehni sp. nov. / Alekseev et Bukejs des. 2024” [red printed label]; adult, sex unknown. A complete beetle included in a transparent, yellow amber piece with dimensions of 17× 6 mm and a maximum thickness of 3 mm, preserved without supplementary fixation. Syninclusions: several stellate Fagaceae trichomes.

Paratype: No. KA-CLP-001 [ CKVA]; “Paratype / Helioctamenus / groehni sp. nov. / Alekseev et Bukejs des. 2024” [red handwritten label]; adult, sex unknown. A complete beetle with partially exposed metathoracic wings included in a transparent, yellow amber piece with dimensions of 26× 18 mm and a maximum thickness of 7 mm, preserved without supplementary fixation. Syninclusions: one specimen of Nematocera ( Diptera ).

Type stratum. Baltic amber from Eocene amber-bearing Blaue Erde deposits; estimated age: middle–late Eocene (Standke 1998).

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

Description of holotype. Measurements: total body length (including visible part of head) 3.1 mm, maximum body width (across elytra) 1.15 mm; head length 0.5 mm, head maximum width (across eyes) 0.7 mm; pronotal length 0.6 mm, maximum pronotal width 0.7 mm, basal pronotal width 0.6 mm; elytral length (along elytral suture, including scutellum) 2.0 mm.

Body subparallel-sided, elongate, about 3.3× as long as wide, weakly convex dorsally and ventrally, unicolorous dark brown. Pubescence: head and pronotum with short, strongly curved, decumbent, narrow setae; elytra with short, slightly curved, semierect, narrow setae arranged in regular rows and not forming pattern.

Head prognathous, transverse; densely granulose dorsally, with granules round, about as wide as diameter of eye facet, and each granule bearing seta; covered with coarse punctures ventrally. Anterior margin of clypeus widely rounded. Compound eyes hemispherical, strongly protruding, with coarse facets, without interfacetal setae. Antennal insertions concealed dorsally, distant from eyes; antennal grooves ventrad eye indistinct. Antennae short, extending to about midlength of pronotum; sparsely covered with short setae; 11-segmented without distinctly separated antennal club; scape invisible from above, cylindrical; pedicel cylindrical, slightly elongate, 1.15× as long as wide, about as wide as scape; antennomere 3 conical, slightly dilated apically, elongate, about 1.4× as long as wide, about 1.35× as long as pedicel; antennomere 4 subtrapezoidal, 1.2× as long as wide, about 0.7× as long as antennomere 3; antennomeres 5–8 subquadratic, nearly as long as wide; antennomere 9 subtrapezoidal, slightly dilated apically, 1.3× as wide as long, slightly wider than antennomere 8; antennomere 10 trapezoidal, dilated apically, transverse, 1.7× as wide long, distinctly wider than antennomere 9; antennomere 11 circular, as long as wide, with widely rounded apex, 0.7× as wide as antennomere 10. Maxillary palp with four palpomeres; palpomere 1 smallest, subtriangular; palpomeres 2 and 3 subquadratic, about as long as wide; palpomere 4 elongate oval, truncate, about 1.9× as long as palpomere 3. Terminal labial palpomere triangular, acute apically.

Pronotum subquadrate, slightly transverse, 1.16× as wide as long, widest at anterior angles, weakly narrowed posteriad, maximum pronotal width / basal pronotal width = 1.16; pronotal disc convex, uneven, longitudinally impressed medially, sloped at lateral sides; pronotal surface densely granulose, with distance between granules smaller than diameter of one granule, and each round granule bearing seta. Pronotal lateral margins subparallel, finely denticulate; basal margin widely rounded medially; anterior margin with weakly rounded middle lobe. Anterior pronotal angles distinct, rectangular; posterior angles obtuse. Prohypomera concave, densely punctate. Prosternum convex, densely covered with coarse punctuation. Intercoxal prosternal process elongate, extending slightly beyond posterior margin of procoxae, with subparallel lateral margins, rounded apically, rather wide, about as wide as diameter of procoxa. Procoxal cavities open posteriorly.

Scutellar shield distinct, small, almost circular.

Elytra almost parallel-sided within anterior two-thirds of their lengths, tapered apically, about 1.7× as long as wide combined, convex, without carinae, distinctly wider than pronotum basally, 3.3× as long as pronotum. Humeri well-developed; humeral angles rounded. Elytra striate-punctate. Scutellary striole absent. Elytral striae with rows of dense, elongate granules; intervals flat, with micropunctation. Epipleura well-developed, widest in basal half, slightly narrowing posteriad, punctate, reaching elytral apices. Mesocoxal cavities closed. Metanepisternum narrow, about 7.0× as long as wide, punctate, with lateral margins slightly emarginate. Metaventrite slightly convex, distinctly longer than abdominal ventrite 1, densely covered with coarse punctation, with distance between punctures distinctly smaller than diameter of one puncture; discrimen distinct in posterior half.

Legs rather short and robust, finely punctate and sparsely setose. Procoxa small, nearly rounded, separated by about one diameter of procoxa; mesocoxae hemispherical, narrowly separated by about 0.2× diameter of mesocoxa; metacoxae widely oval, transverse, narrowly separated by about 0.5× longitudinal diameter of metacoxa. Femora nearly spindle-shaped, slightly flattened, widened medially. Tibiae straight; tibiae and femora subequal in length. Tarsal formula 4-4-4; tarsomeres simple, non-lobed, with fine setation ventrally; tarsomeres 1–3 subequal in length and shape, cylindrical; tarsomere 4 longest, about as long as tarsomeres 1–3 combined, slightly curved. Claws simple, large, about 0.3× as long as tarsomere 4.

Abdomen with five visible ventrites; densely covered with fine punctuation, distance between punctures equal to 0.5–1.0× diameter of one puncture; abdominal sutures distinct throughout length. Relative length ratios of ventrites 1–5 equal to 22:17:14:10:13. Abdominal ventrite 1 with triangular, apically rounded intercoxal process. Abdominal ventrite 5 with widely rounded posterior margin, weakly concave towards apex.

Paratype. No. GPIH no. 5217, CCGG no. 8707 ( Figs 22–24 ). Measurements: total body length (including visible part of head) 3.1 mm, maximum body width (across elytra) 1.1 mm; head length 0.3 mm, head maximum width (across eyes) 0.6 mm; pronotal length 0.7 mm, maximum pronotal width 0.8 mm, basal pronotal width 0.75 mm; elytral length (along elytral suture, including scutellum) 2.1 mm. Elytral surface of paratype is visually represented by coarse, apparently irregular, and generally homogenous sculpture, which consists of rounded forms of variable size—this significantly differs from striate-punctate elytra of the holotype, which are covered with regularly arranged elongate granules. We interpreted this apparent difference as probable contamination covering beetle dorsum (i.e., wood dust and air covering this region within resin), and not natural elements of dorsal sculpture with species-level significance.

Paratype. No. KA-CLP-001 [CKVA] ( Figs 25–26 ). Measurements: total body length (including visible part of head) 3.1 mm, maximum body width (across elytra) 1.2 mm; head length 0.2 mm, head maximum width (across eyes) 0.7 mm; pronotal length 0.8 mm, maximum pronotal width 0.8 mm, basal pronotal width 0.75 mm; elytral length (along elytral suture, including scutellum) 2.1 mm. Discrimen distinct in posterior two-thirds of metaventrite. Metathoracic wings well developed. Otherwise, this specimen is similar in all visible morphological characters to holotype No. 5209 [GPIH].

Differential diagnosis. Helioctamenus groehni sp. nov. differs from all extant congeners in possessing the following combination of characters: antennae distinctly 11-segmented with antennomere 11 well-developed, not fused with previous antennomere, and as long as antennomere 10; elytral intervals flat, not carinate; humeri well-developed; metathoracic wings well developed; pronotum distinctly narrower than elytral base; and scutellar shield distinct. The elongate body of the new species resembles such species as H. bedeli Dajoz, 1971 , H. fumicornis (Bedel, 1891) , and H. occidentalis Oromí, 1984 , but distinctly differs from shorter and more oval bodies of H. gineri ( Español, 1948) and H. lusitanicus Reitter, 1903 .

Among the zopherids described from Baltic amber, the new species is the first described representative of the tribe Sarrotriini , thus H. groehni sp. nov. may be distinguished by the set of the tribal level characters that include: antennae setose, 11-segmented, without distinctly separated antennal club; wide prosternal process; and intercoxal abdominal process triangular, rounded apically. The new species may be confused only with the apparently similar Xylolaemus legalovi Alekseev et Bukejs , but differs from it in the non-explanate lateral pronotal sides, elytral intervals flat and elytra without additional setose patches consisting of lanceolate scales.

Derivatio nominis. The specific epithet is a patronym; the new species is named in honor of Mr. Carsten Gröhn (Glinde, Germany), an enthusiast and specialist in Baltic amber.

Distribution of congeners. The genus Helioctamenus is currently distributed in the Mediterranean region ( Dajoz 1971; Ślipiński & Schuh 2008), namely in the Iberian Peninsula (3 species), Baleares (1 species), Canary Islands (2 species), and North Africa (4 species). In total, ten species are known: H. bedeli Dajoz, 1971 ; H. curticornis Pic, 1922 ; H. espanoli Cobos, 1950 ; H. fernandezi Cobos, 1965 ; H. fumicornis (Bedel, 1891) ; H. gineri ( Español, 1948) ; H. hippopotamus Schaufuss, 1882 ; H. lusitanicus Reitter, 1903 ; H. occidentalis Oromí, 1984 ; and H. pardoi Español, 1957 . The first extinct species described in the current paper confirms the presence of the genus in the Paleogene of the Western Palearctic.

Ecology of congeners. Recent representatives of Helioctamenus are more or less xerophilous, occurring in dry habitats, under stones or plants ( Dajoz 1971). Helioctamenus hippopotamus Schaufuss, 1882 was collected “sub lapidibus magnus” [under large stones] ( Schaufuss 1882), and the type series of H. occidentalis was sampled on lichens and epiphytic mosses of Erica scoparia ( Oromí 1984) . The newly described Eocene Helioctamenus was most likely also associated with a xerophilous community, possibly consisting of epiphytic mosses and lichens on tree bark of trunks, or it could be ground-living, occurring under lichens in sun-exposed microhabitats of the amberiferous forest. Records of different lichens in Baltic amber are known and not rare (e.g., Rikkinen 2003; Rikkinen et al. 2018; Kaasalainen et al. 2019), thus a lichen-related habitat for extinct species may be the most likely analogue among Recent relatives.

Figures

FIGURES 17–19. Helioctamenus groehni sp. nov., holotype, No. 5209 [GPIH]: 17—habitus, dorsal view; 18—habitus, ventral view; 19—habitus, dorso-lateral view. Scale bar = 0.5 mm.

FIGURES 20–21. Helioctamenus groehni sp. nov., holotype, No. 5209 [GPIH]: 20—habitus, left lateral view; 21—details of anterior part of body, dorso-lateral view.Abbreviations: a1–a11—antennomeres 1–11, respectively. Scale bars = 1.0 mm for Fig. 20; 0.25 mm for Fig. 21.

FIGURES 22–24. Helioctamenus groehni sp. nov., paratype, No. 5217 [GPIH]: 22—habitus, dorsal view; 23—habitus, ventral view; 24—habitus, left lateral view. Scale bar = 0.5 mm.

FIGURES 25–26. Helioctamenus groehni sp. nov., paratype, KA-CLP-001 [CKVA]: 25—habitus, dorsal view; 26—habitus, ventral view. Scale bar = 0.5 mm.