Miculissima excavata, Jan & ºimon-Pražák & Yamamoto & Lackner & Fikáček & Prokop & Michael & Caterino, 2024

Simon-Pražák, Jan, Yamamoto, Shûhei, Lackner, Tomáš, Fikáček, Martin, Prokop, Jakub & Caterino, Michael S, 2024, A bonanza of Cretaceous fossils provides insights into the evolution of antennal protection in clown beetles (Coleoptera: Histeridae), Zoological Journal of the Linnean Society (zlae 137) 202 (3), pp. 1-28 : 20-22

Miculissima excavata sp. nov.

( Fig. 13 )

Material: Kachin amber (c. 99 Mya). Amber piece dimensions: 9 × 25 × 2 mm. Amber clear with several insect fragments and air bubbles. Deposited at HUM ( SEHU-0000121230 ) .

Measurements: Head width: 0.24 mm; width between anterior pronotal angles: 0.26 mm; width between posterior pronotal angles: 0.46 mm; pronotal length: 0.22 mm; sutural elytral length: 0.6 mm; elytral width (in pair, across widest point): 0.54 mm.— Body: Oval and elongate. Dorsal cuticle glabrous with irregular longitudinaldeformationsintherightside.Colourreddishbrown to black.— Head: Frons smooth, flat, and wide, slightly elevated above antennal bases. Frontal stria absent. Clypeus convex, elevated along midline, truncate apically. Labrum short and wide, rounded apically, with a prominent seta on each side. Mandibles mostly retracted. Terminal maxillary palpomere swollen at base, pointed apically, slightly concave on inner margin, 4× as long as maxillary palpomere 3. Maxillary palpomere 2 twice as long as palpomere 3. Terminal labial palpomere oblong, widest medially. Antennal scape simple, slightly curved. Pedicel slender, as long as antennomeres 3–4; Antennomeres 3–8 equal in shape and length, simple square shaped, widening slightly from 3 to 8. Antennal club round, undivided, but with two setose, outwardly arcuate annuli. Eyes convex, coarsely faceted, well visible from above.— Thorax: Pronotal disc smooth, slightly convex. Basal pronotal margin widely angular. Posterolateral pronotal corners curved and pointed posteriorly. Right-half of pronotal disc is irregularly deformed. Marginal pronotal stria present, complete. Lateral pronotal stria present, marginal bead elevated. Scutellar shield tiny, triangular. Elytra smooth, elongate, slightly convex, with very fine, scratch-like striae at outer base. Right elytron irregularly deformed. Epipleural stria not apparent. Wings present (visible extending beyond elytra). Prosternum short and wide, with a very short prosternal lobe; prosternum incised at sides for passage of antennal funicle; antennal cavity widely open beneath (prosternal alae absent). Prosternal keel weakly emarginate at base, obscured by debris. Mesoventrite smooth and relatively narrow (length: width ratio 1: 2), weakly produced anteriorly, without striae. Mesometaventral suture visible as a thin line. Metaventrite slightly concave medially. Lateral metaventral stria present in anterior third of the metaventral disc, curved laterally extending to metepisternum, which is narrow, but exposed over its entire length.— Legs: Profemur carinate, with a row of tiny setae along inner margin and a simple groove for protibial reception. Protibia dilated in apical two-thirds, with a simple tarsal groove, with several minute setae apically on inner margin; outer protibial margin smooth, but with a couple spines near the widest part of tibia. Protibia apical margin oblique, lacking apical spurs; Mesofemur slender, swollen medially. Mesotibia widened (slightly less than protibia), gradually expanding apically with a simple tarsal groove and a tiny tibial spur. Meso- and metatarsi similar to protarsus. Metafemur long and slender. Metatibia very slightly widened to apex, with minute setae in apical half of inner margin and a small tibial spur. Tarsi 5-5-5, all basal tarsomeres bearing a prominent pair of apical setae beneath, some with sparse secondary setae as well; protarsus simple, terminal tarsomere as long as tarsomeres 2–4 combined. Mesotarsus similar in shape. Metatarsomere 1 shortened, half of the length of metatarsomere 2.— Abdomen: First abdominal ventrite smooth, with two widely separated parallel lateral striae, posterior margin widely emarginate. Pygidium smooth.

Taxonomic assignment: The absence of a distinct pronotal lobe, minute body size, and simple legs would suggest a relation to Abraeinae ( Wenzel 1944) . Labrum with two prominent lateral setae ( Fig. 13D ) and convex eyes ( Fig. 13E ) are also typical among the subfamily. The species exhibits a distinctly annulate antennal club ( Fig. 13C )—a plesiomorphy found within Abraeinae only in Acritomorphini ( Wenzel 1944, Mazur 1997). The excavate and sculptured pronotal hypomeron ( Fig. 13D, E ) is unlike any in recent Histeridae taxa. The phylogenetic analyses did not resolve the position of this taxon and placed it either as sister to all Abraeinae or to all Histeridae excl. Abraeinae and Antigracilinae . Thus, a subfamily placement is unclear.

Diagnosis: Glabrous surface. Frons flat, wide, clypeus convex, labrum short and wide, with a pair of prominent setae laterally. Eyes convex. Pronotum widely angular posteriorly, with complete marginal stria and a lateral pronotal stria. Prosternal hypomeron widely excavate and irregularly structured, with a weakly defined antennal cavity. Tibiae simple, slightly widened, with several spines. The species may resemble small abraeines found in Burmese amber—herein described Palaeabraeus glabrus and Pseudacritus extinctus . It is distinguishable from both by the more prolonged body shape and the strongly excavated hypomeron.

Etymology: The Latin adjective ‘excavata’ refers to the excavate hypomeron.

Additional reports

Some additional newly discovered specimens have shed light on characters poorly or not at all visible in previously published reports, or have expanded the spatial and temporal range in the fossil record:

Figures

Figure 13. Miculissima excavata gen. et sp.nov.. A, dorsal view. B, frontal view.C, ventral view.D, lateral view. E, lateral view. Abbreviations:aca, antennal cavity; acl, antennal club; ga, galea; lp, labial palpus; ls, labral setae; mp, maxillary palpus; pl, prosternal lobe.