Ataenius damzeni Bukejs & Alekseev, 2018

Bukejs, Andris & Alekseev, Vitalii I., 2018, A new extinct species of Ataenius Harold from Baltic amber (Coleoptera: Scarabaeidae: Aphodiinae), Zootaxa 4442 (1), pp. 153-160 : 154-158

Ataenius damzeni Bukejs & Alekseev , new species

( Figs. 1–7 )

Type material. Holotype: “5953-01” (MAIG), adult, complete, sex unknown. Ventral side of specimen partially obscured by “milky” opacity. Paratype: “5953-02” (MAIG), adult, complete, sex unknown.

Additional material examined. “5953-03” ( MAIG), adult, damaged specimen without head, sex unknown. Dorsal side of specimen partially and ventral side of specimen almost completely obscured by “milky” opacity. “5953-04” ( MAIG), adult, damaged specimen with separated pronotum and head, sex unknown.

Type strata. Baltic amber, mid-Eocene to Upper Eocene.

Type locality. Baltic Sea coast, Yantarny settlement [formerly Palmnicken], Kaliningrad region, Russia.

Description. Habitus. Body moderately convex, elongate oval, subparallel sided, slightly alutaceous, unicolorous black (as preserved), glabrous. Total body length 2.8 mm (excluding head); body width 1.5 mm.

Head. Head transverse, convex, without transverse carina, slightly narrower than pronotal anterior margin; anterior half of head with microreticulation and sparse, very fine punctures, and posterior half with dense, fine punctures. Distance between punctures approximately 0.5–1.5× diameter of one puncture. Clypeus dilated, covering mouthparts; clypeal margin narrowly reflexed, rounded on each side of shallow, wide, median emargination; sides almost straight anterior to genae. Frontal suture shallow, and trisinuate. Compound eyes not visible from directly above. Antennae not visible in examined specimens.

Thorax. Pronotum transverse, about 1.5× as wide as long, and not explanate. Disc evenly and slightly convex, anterolateral region with slightly expanded area. Pronotal punctation distinctly unequal in size: dense and small in anterior one-third of pronotal length, and distinctly larger and sparser posteriorly. Distance between punctures approximately 0.5–3.0× diameter of one puncture, interspaces with secondary punctation and microreticulation. Posterior pronotal margin slightly convex, narrowly bordered, and crenulate. Lateral margins slightly and evenly convex, slightly upturned, narrowly bordered, crenulate, without setae or scales. Anterior margin straight and without bordering. Anterior angles obtusely rounded, protruding; posterior angles widely rounded.

Scutellar shield relatively small, elongate, rounded apically, about 1.7× as long as wide, with fine punctures.

Elytra subparallel-sided, slightly tapering posteriorly, moderately convex, elongate, about 1.6× as long as their combined width, 2.0× as long as pronotum, and widest at mid-length. Anterior margin of elytra slightly narrower than pronotum; lateral margins without setae. Humerus apparently without distinct denticle. Each elytron with 10 deep, punctate striae; punctures small, shallow, apparently elongate. Interstriae distinctly convex, with microreticulation and minute secondary punctation; elytral interstriae equal in height. Epipleura wide at humeri and gradually narrowing toward elytral apex, reaching elytral apex.

Hypomeron finely and densely punctate. Mesosternum carinate between coxae; mesocoxae distinctly separated from epipleura. Metasternum slightly convex; disc almost flat with midline impressed, with sparse, small punctures; lateral area and lateral metasternal triangle impunctate and scabrous.

Legs. Profemur wide, about 1.6× as long as wide, with few fine punctures; perimarginal groove distinct; posterior margin with short, erect seta medially. Meso- and metafemora narrower than profemur, nearly equal in size, with few fine punctures, and sharp posterior femoral line. Protibia rather short, flattened and strongly expanded in apical portion, impunctate, nearly as long as profemur; protibia with terminal spur, slightly arcuate ventrally; with three large outer denticles in apical half. Meso- and metatibiae weakly expanded apically, without oblique carinae; with two terminal spurs of unequal length, located close together and below tarsal insertion, superior spur about as long as tarsomere 1 and about 2× as long as inferior spur; apex of meso- and metatibia bearing fringe of spine-like accessory setae that are unequal in size, and accessory spine apparently lacking. Tarsi slender, 5-segmented, without dense setae ventrally, and with few setae apically. Meso- and metatarsi nearly as long as adjacent tibiae; meso- and metatarsomere 1 about as long as superior tibial spur, and about 1.2–1.4× as long as tarsomeres 2–5 combined. Claws small, simple, symmetrical.

Abdomen. Shiny, with five visible, coalesced ventrites. Ventrite 1 impunctate, scabrous, with slightly elevated triangular area anteromedially; ventrites 2–5 with small, sparse punctures; punctation of ventrites 2 and 3 slightly sparser. Ventrites 2–5 fluted along anterior margin; ventrites 2 and 5 finely fluted, and ventrites 3 and 4 with stronger fluting. Ventrite 5 with two erect setae on disc. Relative length ratios of ventrites 1–5 (medially) equal to 9:10:10:10:10. Pygidium partially exposed, and apparently with short median transverse carina; pygidial surface scabrous and slightly semicircularly impressed in apical portion; bearing two erect setae near anterior margin.

Variability. Body length excluding head (head turned downwards) 2.8–2.9 mm, maximum width 1.5 mm. Holotype: “5953-01” 2.8 mm long excluding head, and 1.5 mm wide; paratype: “5953-02” 2.8 mm long excluding head, and 1.5 mm wide; additional specimens: “5953-03” 2.9 mm long excluding head, and 1.5 mm wide; “5953- 04” not measured because of poor preservation.

Paratype and two additional specimens slightly differs in body length; otherwise apparently similar in all visible morphological characters to the holotype. Two additional specimens are not sufficiently visible or damaged (see material description) therefore they not included in the type serie.

Etymology. The specific epithet is a patronym dedicated to Mr. Jonas Damzen (Vilnius, Lithuania), the collector of the amber piece.

Differential diagnosis. Ataenius damzeni , new species differs from scarabaeids previously described from Baltic amber ( Ataenius europaeus , Saprosites succini , and Airapus lithuanicus ) in possessing: (1) glabrous elytral interstriae without granulation and setation; (2) metatarsomere 1 slightly shorter than metatarsomeres 2–5 combined; (3) meso- and metatibiae with two terminal spurs of unequal length; (4) anterior portion of head with sparse and very fine punctation; (5) pronotal base narrowly bordered; (6) pronotal punctation distinctly unequal in size, with dense and small punctures anteriorly, and larger and sparser punctures posteriorly; (7) pronotal lateral margins crenulate, without setae or scales; and (8) smaller body size. See also details provided in key below.

This new fossil species differs from extant congeners of the genus ( Cartwright 1974; Stebnicka 2001, 2003; Smith & Skelley 2007; Stebnicka & Lago 2005) in the combination of the following characters: (1) body without argillaceous coating; (2) clypeus broadly rounded each side of shallow median emargination (without trace of clypeal denticles); (3) head finely punctate; (4) pronotal punctation heterogeneous; (5) pronotal disc evenly convex; (6) lateral pronotal margins slightly upturned, narrowly bordered, crenulate, without setae or scales; (7) scutellar shield oblong; (8) mesosternum carinate between coxae; (9) elytra subparallel-sided; (10) elytral interstrial intervals convex, equal in height; (11) body ventral surface shiny; and (12) abdominal ventrites 2–5 distinctly punctate.

Figures

FIGURES 1–2. Ataenius damzeni Bukejs & Alekseev, new species, holotype “5953-01”. 1, habitus, dorsofrontal view; 2, habitus, ventrolateral view. Scale bar = 1 mm.

FIGURES 3–4. Ataenius damzeni Bukejs & Alekseev, new species, paratype “5953-02”. 3, habitus, lateral view; 4, habitus, laterocaudal view. Scale bar = 1 mm.

FIGURES 5–7. Ataenius damzeni Bukejs & Alekseev, new species. 5, general view of amber piece “5953” with specimen enumeration (1—holotype; 2—paratype; 3‒4—non-type specimens); 6, details of pronotum and head, dorsofrontal view (holotype “5953-01”); 7, details of abdomen and hind left leg (holotype “5953-01”). Scale bar = 5 mm for Fig. 5; 0.25 mm for Figs. 6 and 7.