Heterelmis groehni, Bukejs, Andris, Alekseev, Vitalii I. & Jäch, Manfred A., 2015

Bukejs, Andris, Alekseev, Vitalii I. & Jäch, Manfred A., 2015, The riffle beetles (Coleoptera: Elmidae) of the Eocene Baltic amber: Heterelmis groehni sp. nov. and Heterlimnius samlandicus (Bollow, 1940) comb. nov., Zootaxa 3986 (4), pp. 452-460 : 456-458

Heterelmis groehni sp. nov.

( Figs 5–6 )

Material examined. Holotype Nr. C 7712 ( GPIH); sex unknown. A complete specimen with partly exposed hind wings embedded in a small, suboval amber piece (length 24 mm, width 14 mm). Syninclusions: Diptera (three specimens of Ceratopogonidae , and one specimen of? Palaeomedeterus sp., Dolichopodidae ).

Type strata. Baltic Amber, Upper Eocene, Prussian Formation.

Type locality. Yantarny settlement [formerly Palmnicken], Sambian [Samland] Peninsula, Kaliningrad Region, Russia.

Diagnosis. Heterelmis groehni sp. nov. is characterized by the following combination of characters: body size small (1.9 mm long); body form broadly subovate; sublateral pronotal carinae slightly sinuous; transverse pronotal impression distinct, but not very deeply impressed, situated near middle; shallow oblique pronotal impression at base present; each elytron with two carinae (carina on interval 6 extending almost to middle, carina on interval 8 extending to apical 1/4); intercoxal prosternal process comparatively narrow, subtrapezoidal with rounded apex, nearly as long as wide at base; disc of metaventrite moderately convex anteriorly, deeply impressed near middle.

The new species can be distinguished from Heterlimnius samlandicus , by the following characters: distinctly smaller body size ( H. samlandicus : 3.25 mm long, 1.65 mm wide); presence of carinae on pronotum and two carinae on each elytron; shape and punctation of elytra.

Heterelmis groehni sp. nov. is distinctly smaller in body size than most other taxa described in this genus, for instance H. apicata (Grouvelle, 1896) (2.8–3.2 mm), H. convexicollis Delève, 1968 (2.5 mm), H. impressicollis Delève, 1968 (2.7 mm), H. longula Sharp, 1887 (3.5–4.0 mm), H. lucida Delève, 1968 (3.1 mm), H. neglecta (Grouvelle, 1896) (3.0 mm), H. obesa obesa Sharp, 1882 (2.3–2.5 mm), H. stephani Brown, 1972 (2.3–2.6 mm). The new species clearly differs from H. obscura Sharp, 1882 , H. tarsalis Hinton, 1940 , H. vilcanota Spangler, 1980 , and Heterelmis vulnerata (Leconte, 1874) in the narrower prosternal process. It differs from H. comalensis Bosse et al., 1988 in dark color, and wider body form; from H. gibbosa Grouvelle, 1889 , H. obesa plana Hinton, 1940 , H. simplex Sharp, 1882 , and H. stephani Brown, 1972 , among other characters, in the presence of a distinct medial transverse pronotal impression.

Description. Body length 1.9 mm, maximum width 0.95 mm; subovate, subparallel-sided, convex dorsally and ventrally; unicolorous black. Pronotum, elytra, medial part of pro- and metaventrite, and middle part of abdominal ventrite 1 sparsely covered with moderately long, pale recumbent setae; pronotal setae directed to center of disc, elytral setae directed posteriad. Hypomera, lateral parts of prosternum, meso- and metaventrite, epipleura, abdomen (except middle part of ventrite 1), coxae, femora with very dense, short, recumbent grayish-golden setae; tibiae, tarsi and antennae with less dense, short recumbent greyish-golden pubescence.

Head prognathous, together with eyes not wider than pronotum. Eyes moderately large (subequal in size to procoxa), convex, with moderately large and distinct facets. Clypeus without distinct punctures, with widely emarginate anterior margin. Labrum transverse, about 1.8 times as wide as long, with widely rounded anterior margin; apparently with fine punctures. Maxillary palpi 4-segmented, palpomere 4 elongate with rounded apex. Apices of labial palpi truncate. Antennae filiform, long, extending to base of pronotum; 11-segmented, scape and pedicel widest, subcylindrical; antennomeres 3–8 weakly dilated apically, subequal in length and shape; antennomeres 9–10 elongated, slightly longer than antennomere 8; antennomere 11 longest, about 1.3 times as long as antennomere 10, with pointed apex; relative length ratios of antennomeres 1–11 equal to 7:7:6:4:4:4:5:5:6:7:11.

Pronotum subtrapezoidal, weakly transverse, about 1.15 times as wide as long, widest near base; slightly narrowed posteriad, more distinctly narrowed anteriad; with sinuous sublateral carinae, which extend from base to anterior margin; with moderately deep transverse depression nearly at middle, and with shallow oblique impression at the base; disc convex, lateral sides rather sloping. Pronotal punctation fine (distinctly smaller than eye facet) and sparse, distance between punctures markedly greater than puncture diameter; interspaces smooth and shiny; apparently antero-lateral parts of pronotum with fine and dense secondary punctures. Lateral margins crenulate, slightly bisinuate, with narrow bordering; posterior margin trisinuate, without distinct narrow bordering; anterior margin convex, with narrow bordering. Posterior angles nearly rectangular; anterior angles acute, distinctly produced anteriad.

Scutellum moderately large, oval, pointed apically; about 1.35 times as long as wide; flat. Elytra suboval, 1.4 times as long as wide, widest at the middle; convex at disk and rather steeply sloping at sides. Basal margin bisinuate, with very fine crenulation (distinctly visible at middle); lateral sides nearly parallel in basal 1/3, weakly rounded at middle, and strongly narrowed in apical 1/5. Elytra with subparallel carinae on intervals 6 and 8; carina on interval 6 extending almost to middle; carina on interval 8 extending almost to apex. Elytral punctures small (slightly larger than pronotal punctures) and sparse, arranged in somewhat irregular longitudinal rows, distance between them markedly larger than puncture diameter; distance between punctures in striae equal to 2–5 diameters of a puncture; intervals flat, only on disc slightly convex. Accessory stria absent. Hind wings present.

Prosternum, metaventrite and middle part of abdominal ventrite 1 with fine and sparse punctation (as on pronotum), distance between punctures markedly greater than a puncture diameter, interspaces shiny. Hypomera weakly impressed in anterior 2/3. Prosternum produced anteriad, convex with flattened disc. Intercoxal prosternal process subtrapezoidal with rounded apex, nearly as long as wide at base, lateral margins slightly concave; at apex nearly as wide as transverse diameter of procoxa, at base 1.7 times as wide as transverse diameter of procoxa; distinctly impressed in apical half. Procoxae globose, distance between them nearly equal to 1.3 transverse diameters of procoxa. Trochantins not exposed. Mesoventrite with microsculpture (especially distinct anterolaterally); disc widely and deeply impressed. Mesocoxae nearly globose, distance between about 1.3 times as wide as transverse diameter of mesocoxa. Metaventrite with longitudinal medial groove; disc moderately convex anteriorly, deeply impressed near middle; posterior margin with triangular excision medially (between metacoxae). Metacoxae elongate, transverse, about 2.5 times as wide as long; distance between them about 0.6 times transverse diameter of metacoxa. Metepisternum with nearly straight lateral margins, about 6.5 times as long as wide. Epipleura wide, not reaching elytral apex.

Abdomen with five ventrites. Ventrite 1 distinctly longer than ventrite 2, anterior margin between metacoxae triangularly produced, glabrous median part laterally bordered by longitudinal carinae. Ventrites 3 and 4 equal in length. Posterior margins of ventrites 1–4 concave. Lateral margins of ventrite 5 forming teeth in apical 1/3 and then strongly narrowed to apex. Relative length ratios of ventrites 1–5 equal to 6:4:3:3:6.

Legs relatively long and slender. Trochanters elongate. Femora weakly widened medially, subflattened. Tibiae slightly curved, with almost parallel sides, about 1.1 times as long as femora, metatibiae about 1.5 times as wide as metafemora; with few thin spines apically. Tarsi long and thin; tarsomeres subcylindrical, not lobed, each tarsomere with few thin small spines ventrally; metatarsi as long as metatibia; relative length ratios of metatarsomeres 1–5 equal to 7:5:5:6:15; tarsal formula 5–5–5. Claws simple, thin, and long (nearly as long as tarsomeres 1–2 combined); slightly curved; located close to each other.

Etymology. Patronymic, this new species is named after Carsten Gröhn (Glinde, Germany), who enabled us to study this specimen.

Figures

FIGURES 5 – 6. Heterelmis groehni sp. nov., holotype, C 7712: 5 — habitus, dorsal view; 6 — habitus, ventral view.