Cupes balticus, Yamamoto, 2024

Yamamoto, Shûhei, 2024, A new fossil species of the reticulated beetle genus Cupes (Coleoptera: Archostemata: Cupedidae) from Eocene Baltic amber, Zootaxa 5432 (4), pp. 451-460 : 452-458

Cupes balticus sp. n.

Figs. 1–4 .

Type material. Holotype, a complete adult of undetermined sex, preserved in a yellowish-transparent, flattened rectangular parallelepiped piece (dimensions, ca. 18.0× 10.6× 3.7 mm) of Baltic amber, with the accession number SEHU-0000121237 , deposited at the Laboratory of Systematic Entomology ( SEHU), the Hokkaido University Museum (HUM), Hokkaido University, Sapporo, Japan. Syninclusion: a tiny Collembola.

Type locality and horizon. Russia: Kaliningrad Oblast; middle to upper Eocene .

Etymology. The specific epithet balticus refers to the occurrence of the type material in Baltic amber from near the Baltic Sea Coast, also emphasizing the potentially higher diversity and abundance of Cupes beetles in this amber deposit.

Diagnosis. Body of relatively large size (9.3 mm long) as Cupes species in Baltic amber, with a peculiar bi-colored pattern on elytra by scales, consisting of brownish and yellowish grey spots (head, median longitudinal stripe on pronotum, and elytral apex brownish); head with 2 pairs of dorsal paramedian tubercles well raised, with temples only slightly shorter than eyes; antenna with antennomere 3 almost twice as long as antennomere 2, as well as moderately narrowly elongate terminal antennomere (about 3.8 times as long as thick); pronotum wider than head, anterolaterally projecting and laterally broadly angulate, with an anteriorly widened medial elevated stripe without a clear longitudinal furrow; hind leg with comaratively short metatarsomere 5 (metatarsomere 1 distinctly less than twice as long as metatarsomere 5).

Description. Body ( Fig. 1 ) narrowly elongate, relatively large, 9.32 mm long, moderately convex dorsally, flattened ventrally, widest at posterior part of elytra. Surface with extremely dense scales, masking coloration of body surface; scales on head, pronotum (including pronotal median longitudinal stripe) dark brown; elytra bi-colored, with a characteristic pattern of brownish and yellowish grey spots, with brownish apex (both subapical and apical bands without interruption); body ventrally with extremely dense, yellowish grey scales; surface on antennae and legs scales gradually transforming into subrecumbent, rather stout setae.

Head ( Figs. 2A, B , 3A, B ) weakly transverse, widest across eyes, 1.06 mm long, 1.60 mm wide (including eyes), moderately narrower than pronotum. Surface of head with 2 paramedian pairs of dorsal tubercles, both well raised dorsally and swollen; anterior tubercles or protuberances (p1) rather rectangular, transverse, with their base closed; posterior protuberances (p2) elongate-oval, with more raised anterior half, their bases separated by a relatively wide and elevated median stripe divided by a longitudinal furrow (fv). Eyes ( Figs. 2A, B , 3A, B , ey) rather small, as wide as scape, only slightly longer than temples, moderately protuberant laterally. Temples ( Figs. 2A, B , 3A, B , tmp) long, prominent. Gular sutures apparently subparallel-sided, narrowly separated. Antennal insertions divided by distance about as wide as length of scape ( Fig. 3A, B ). Antennae ( Figs. 1 , 2F , 4C ) 11-segmented, filiform, somewhat slender, about 0.6 time as long as body (5.53 mm, left), barely reaching to middle of elytra; scape (antennomere 1, a1) approximately oval, 1.5 times as long as thick; pedicel (antennomere 2) short, as long as thick, wider than scape; antennomere 3 narrowly elongate, moderately dilated towards apex, nearly about twice as long as 2nd, slightly longer than 4th; antennomeres 4–10 each narrowly elongate, subcylindrical, gradually narrowing distally; ultimate antennomere less than 4 times as long as thick (3.8 times as long as thick on left side). Labrum scarcely visible.

Pronotum ( Figs. 2A, C , 3C, D , pn) subtrapezoidal, moderately transverse, widest at about half length, narrower than elytra, 1.29 mm long (along midline), 1.94 mm wide; lateral edges broadly angulate, strongly narrowed in anterior 2/5; anterolateral angles right to obtuse, slightly projecting; posterolateral corners broadly arcuate; posterior margin weakly bisinuate, slightly projecting posteriorly, with a small and weak emargination medially; disc moderately convex dorsally (medial area only, outer areas somewhat explanate), with a median elevated ridge, or stripe, along entire length ( Fig. 3C, D , mrp), as well as a pair of shallow paramedian fossae at anterior edge ( Fig. 3C, D , fs), but lacking a longitudinal furrow along midline. Prosternal process seemingly narrow. Scutellum minute, subquadrangular.

Elytra ( Figs. 1A , 2D ) narrowly elongate, gradually divergent posteriorly, widest in posterior 1/3 (right and left elytron 6.70 mm long from base to apex, right elytron 1.48 mm wide, left elytron 1.79 mm; the distinct difference of the width of the elytra must be an artefact), with acute elytral apices (not emarginate); surface each with 9 longitudinal rows of sub-oval to rounded window-punctures (window-punctures regularly arranged; some punctures rather transverse near base of elytra); 5 interval elevations present, all distinctly raised from base or subbase to apex.

Legs ( Figs. 1 , 2E , 4B, D, E ) moderately long, relatively thick; femora stout, clavate, metafemora not extending beyond lateral edge of posterior body; tibiae slender, bar-like, gradually slightly widened toward apex, much thinner than corresponding femora (but not less than half as wide), with metatibial length of 0.64 mm (left). Tarsi ( Figs. 1 , 2E , 4B, D, E ) 5-segmented, slightly narrower than corresponding tibiae; protarsi ( Fig. 4B, D ) shortened and robust; protarsomere 1 slightly longer than wide, protarsomeres 2–4 subequal in length, each shorter than 1st, ventrally expanded; protarsomere 5 apparently as long as 1st, but apical part not well visible due to milky coarting of micro airbubbles; mesotarsi ( Fig. 4D, E ) slender; mesotarsomere 1 elongate, about twice as long as wide, mesotarsomeres 2–3 subequal in length, each wider than long, shorter than 1st, mesotarsomere 4 slightly longer than 3rd but shorter than 1st, as wide as two preceding segments, mesotarsomere 5 seemingly as long as 1st; metatarsi ( Figs. 2E , 4D, E ) slender; metatarsomere 1 ( Fig. 2E , mtt1) elongate, about 2.9 times as long as wide, about 1.6 times as long as 5th, metatarsomere 2 elongate, sub-cylindrical, about 1.6 times as long as wide, about half as long as 1st, metatarsomere 3 short, very slightly wider than long, distinctly shorter than 2nd, metatarsomere 4 short, widest, bilobed ventrally, moderately longer than 3rd, as long as 2nd, metatarsomere 5 narrowly elongate, slender, strongly dilated apically, widest near apex, about 2.7 times as long as wide. Claws short, simple.

Abdomen ( Figs. 1 , 4D, E ) elongate, apex acute, with five visible ventrites; tergite VIII well sclerotized, semicircular, closely covered with minute setae; ventrite 5 twice as long as 4th; all ventrites except the 1st markedly depressed anteriorly and overlapping the anterior margin of each successive ventrite.

Comparative notes. The new species is most closely related to Cupes weitschati Kirejtshuk, 2005 , characterized by two paramedian pairs of similar dorsal tubercles on the head, comparable eye size, and bi-colored elytra with a distinct pattern. It is differentiated by its anteriorly pointed pronotal corners with angulate lateral margins, uniformly brownish head and pronotum, the presence of two interrupted bands in the apical and subapical parts of the elytra, and a more narrowly elongate ultimate antennomere. Among the Baltic amber cupedid taxa, Cupes balticus sp. n. does not align with the monospecific extinct genus Taxopsis due to its much smaller body size (body length 16.1–18.1 mm in Taxopsis vs. 9.3 mm in the new species), narrowly separated procoxae, and more or less oval-to-polygonal elytral cells (compared to strongly transverse subquadrangular cells in Taxopsis ) ( Kirejtshuk 2005; Kirejtshuk et al. 2016). Distinguished from the other six species of Cupes in Baltic amber, the new species is differentiated by a combination of the following character states ( Kirejtshuk 2005; Kirejtshuk et al. 2016):

—From Cupes rohdendorfi Iablokoff-Khnzorian, 1960 , by having only two paramedian pairs of suboval tubercles on the head dorsum, distinctly smaller eyes, much longer temples, a less elongate terminal antennomere, and the absence of a longitudinal division of the pronotoum by a furrow;

—From Cupes komissari Kirejtshuk, 2005 , by the bi-colored scales on the elytra, only two paramedian prominent pairs of suboval tubercles on the head dorsum, smaller eyes, longer temples, and the absence of a median longitudinal furrow on the pronotum;

—From Cupes kerneggeri Kirejtshuk, 2005 , by much more prominent protuberances on the head dorsum, a large scape as wide as the eye, a more narrowly elongate terminal antennomere, and a prontum with a rounded posterior edge with a weakly sinuate median part;

—From Cupes groehni Kirejtshuk, 2005 , by smaller eyes and longer temples, a shorter and less elongate third antennomere compared to the second, a much less narrowly elongate ultimate antennomere (paratype), an anteriorly projecting pronotal margin, a less elongate first protarsomere, and a less elongate first metatarsomere;

—From Cupes hoffeinsorum Kirejtshuk, 2005 , by partially lighter scales, smaller eyes, longer temples, a vertex with a median longitudinal furrow, a shorter and less elongate third antennomere compared to the second, a much less elongate terminal antennomere, a pronotum wider than the head at temples, and a much shorter fifth metatarsomere compared to the first;

—From Cupes tesselatus (Motschoulsky, 1856) , by the uniformly brownish head and pronotum, smaller eyes with longer temples, a shorter and less elongate third antennomere compared to the second, a more elongate terminal antennomere, a wider pronotum compared to the head at temples, a curved posterior pronotal edge weakly protruding medially, a more narrowly elongate first metatarsomere, and a much shorter fifth metatarsomere compared to the first.

Therefore, the specimen described here differs distinctly from any cupedids previously described from Baltic amber and is thus recognized as a new species.

Figures

FIGURE 1. General habitus of Cupes balticus sp. n., holotype, SEHU-0000121237. A, Dorsal view. B, Ventral view. Scale bars: 3.0 mm.

FIGURE 2. Morphological details of Cupes balticus sp. n., holotype, SEHU-0000121237. A, Head and pronotum, dorsal view. B, Head, dorsal view. C, Right lateral half of pronotum, dorsal view. D, Left elytron and scutellum, dorsal view. E, Right metatarsus, dorsal view. F, Left antenna, dorsal view. Abbreviations: a1–11, antennomeres 1–11; ey, eyes; fv, longitudinal median furrow on vertex; mtt1–5, metatarsomeres 1–5; p1, supraantennal tubercle; p2, supraocular tubercle; tmp, temple. Scale bars: 1.0 mm (A); 0.5 mm (B, C, E); 2.0 mm (D, F).

FIGURE 3. Morphological details of Cupes balticus sp. n., holotype, SEHU-0000121237. A, Head with morphological interpretations, dorsal view. B, Head without morphological interpretations, dorsal view. C, Pronotum with morphological interpretations, dorsal view. C, Pronotum without morphological interpretations, dorsal view.Abbreviations: a1–2, antennomeres 1–2; ey, eyes; fs, paramedian fossae at anterior pronotal edge; fv, longitudinal median furrow on vertex; mrp, median elevated ridge of pronotum; p1, supraantennal tubercle; p2, supraocular tubercle; pn, pronotum; tmp, temple.

FIGURE 4. Morphological details of Cupes balticus sp. n., holotype, SEHU-0000121237.A, Head, right antenna, andprothorax, ventral view. B, Forelegs, ventral view. C, Basal part of left antenna, ventral view. D, Mid- and hindlegs, ventral view. E, Abdomen, ventral view. Abbreviations: a3–6, antennomeres 3–6; v1–5, ventrites 1–5. Scale bars: 1.0 mm (A–D); 2.0 mm (E).