Microdacne Skelley, Leschen & Liu, 2021

Skelley, Paul E., Leschen, Richard A. B. & Liu, Zhenhua, 2021, New Australian Erotylinae with notes on Dacnini (Coleoptera: Cucujoidea Erotylidae), Zootaxa 4948 (3), pp. 363-380 : 368-369

Microdacne Skelley, Leschen & Liu , new genus

Type species. Microdacne gloriousa Skelley, Leschen, and Liu , new species, by present designation.

Diagnosis. A member of the Dacnini with narrow pentamerous tarsi, pronotum anteriorly prominent covering part of head and female genitalia heavily sclerotized. Microdacne is distinguished from other genera by the coarsely faceted eyes, pronotal posterior margin and elytral base with distinct marginal bead, mesoventrite deeply concave between mesocoxae allowing prosternal process to nearly touch metaventrite, mesoventrite with projecting tubercle on each side of concavity that corresponds to shallow depressions on the posterior surface of the prosternal process, shortened elytra with reduced but distinct striae, and in lacking hind wings. Species of this Australian genus show tremendous interspecific variation in the sub-lateral sulcus on pronotum.

Description. 2.7–3.8 mm; width 1.2–1.7 mm. Body elongate oval, dorsally distinctly convex, glossy, mostly glabrous ( Figs. 9–11 ); color pattern generally evident on elytron with 1–2 vague orange or reddish spots at base and apical third, possibly more prominent in life.

Head large compared to rest of body. Fronto-clypeal suture indistinct, complete, straight in middle; sides of head narrowing anteriorly; anterior clypeal margin short, straight. Supraocular stria faint, present from base of eye to clypeus. Eyes coarsely faceted; almost oval, prominent. Stridulatory files on occipital region not observed (heads not removed on few available specimens). Mentum with plate broadly transverse, width> 3× length, coarsely punctate; median projection small. Submentum short, strongly transverse; surface and groove behind with large, deep punctures. Maxilla with terminal palpomere elongate, acuminate at apex; apical sensory area circular. Labium with terminal palpomere slightly wider than maxillary terminal palpomere; apical sensory area elongate and oval, width 2× diameter of sensory area of terminal maxillary palpomere.

Antenna relatively long, slender, club strong moderately tight; antennomere 3 moderately elongate, 1.5× longer than antennomere 4; antennomeres 4–7 as wide as long; antennomeres 3–7 equal in width; antennomere 8 as long as antennomere 7, 1.5× wider than antennomere 7, apically angled at sides; antennomeres 9–11 1.5× longer and 1.5× wider than antennomere 7, subtrapezoidal, apex flat; antennomere 11 transversely elliptical to oval, width slightly less than antennomere 10.

Pronotum strongly convex, almost quadrate; anterior margin lacking marginal bead; anterior angles acute, projecting forward; lateral margin gently arched, convergent anteriorly, with fine marginal bead bearing small punctures; posterior angles sharp, weakly projecting posteriorly; posterior margin of pronotum nearly straight, weakly lobed at middle, marginal bead distinct, groove deep; marginal bead ending at base of sublateral sulcus when present.

Scutellar shield broadly, roundly pentagonal. Elytra short, length at most 1.5× pronotal length; base with marginal bead distinct; lateral margin evenly arcuate from base to apex; humeral protuberances present, weak in dorsal view, in lateral view anterior lateral elytral angle projects forward to meet with posterior angle of pronotum; striae evident, punctures present on disc, reduced laterally; surface smooth; epipleuron wide basally, evenly narrowing to apex; surface glossy, fine punctures with setae sparse. Wings lacking.

Legs and tarsi slender, densely hirsute. Femora fusiform, somewhat flattened, with two sharp edges on inner surface. Tibiae slender, slightly curved basally; apex with fringe of moderately long spinules. Tarsi elongate, cylindrical, tarsomeres 1–4 more or less of same size; tarsomere 5 as long as previous four tarsomeres.

Prosternum convex, glossy, with scattered puncture bearing setae; anterior margin with strong marginal bead; anterior margin of procoxa with line; procoxal lines present between coxa, not extending anteriorly, extending posteriorly onto prosternal process, parallel-sided or arching medially to shallow caudal depression; prosternal process moderately wide, width between procoxa about = transverse diameter of coxa; weakly widened posteriorly; posterior margin with small blunt medial projection, with shallow depressions on each side, prosternal process fits into mesoventrite when body retracted; pores on prosternal process not observed. Hypomeron smooth, glossy, with scattered punctures bearing setae.

Mesoventrite deeply concave between mesocoxae allowing prosternal process to nearly touch metaventrite, with small tubercle on either side of concavity; meso-metaventrite suture broad, distance between mesocoxae 1.5× width of mesocoxa. Metaventrite short, length between meso- and metacoxa equals distance between mesocoxae; anterior margin distinctly bordered medially, reducing to coarse punctures behind mesocoxae; surface with scattered punctures bearing long setae; metathoracic discrimen and coxal lines not present. Metanepisternum narrow. Abdomen with ventrite I anterior process triangular; coxal lines present between coxa, possibly extending onto ventrite 1, short; anterior margin of ventrite 1 behind metacoxae distinctly bordered; surface of all ventrites with scattered punctures bearing long setae.

Male with protibia more arcuate basally; pronotum more elongate; genitalia ( Figs. 14–17 , based on type species) with penis arched, length = 0.6× median strut length; internal sac with patches of microsetae; flagellum with small head, virga short (hidden in microsetae); parameres narrowing apically, with short setae; abdominal sternite IX broad, truncate, spiculum gastrale separated anteriorly by small sclerite.

Female with protibial normally curved at base, pronotum more transverse; genitalia ( Figs. 12–13 ) with segment IX bearing four rows of conspicuous denticulate lamellae, each denticles bearing 3–4 prominent teeth, surface with evenly distributed micro-denticles; coxites undivided, bluntly pointed, sparsely pubescent, with strongly reduced subapical styli on lateral margin of coxite; spermatheca oval with short sclerotized duct ( Fig. 13 ).

Etymology. This genus of Dacnini is one of the smallest members of the tribe. Micro -dacne was chosen to reflect this. Gender feminine.

Remarks. A specimen in the ANIC was tentatively labeled “ Masahiria sp.?”. The genus Masahiria ( Węgrzynowicz 2005) , is a New Caledonian genus that superficially resembles Microdacne . However, Microdacne is most similar to Neothallis (see Delkeskamp 1961) sharing structures of the mesoventrite and having sublateral sulcus on the pronotum. In contrast, Masahiria differs, in part, by lacking sublateral pronotal sulci, lacking basal margins of pronotum and elytra, and lacking visible strial punctures on the elytra. While the mesoventrite is hidden and the prosternal process touches the metaventrite, the mesoventrite of Masahiria does not possess the lateral tubercles. Neothallis differs from both with an elongate body, complete lateral pronotal sulcus, strong elytral striae and having well developed hindwings.

Additional specimens of Microdacne are known but were not available for this work. This is unfortunate because three of these species are described from unique females. Males also have sexual dimorphisms which may show additional characters of use in distinguishing the species. Flightless species of erotylids are often restricted to small distributional ranges or are isolated geographically (e.g., Skelley 1997, 2009). Considering the vast numbers of isolated habitats in Australia, many species of Microdacne are expected to be discovered with future work.

A geographical theme was chosen for the species names. All names proposed here are based on the locality where the species were collected. We hope this theme will continue to be used in the future with newly discovered species.

Figures

FIGURES 9–17. Microdacne gloriousa sp. nov.: 9–11) habitus, holotype; 9) dorsal view; 10) ventral view; 11) lateral view; 12) ovipositor, allotype; 13) spermatheca, allotype; 14–17) Male genitalia, paratype; 14) abdominal segment VIII–IX, ventral view; 15) tegmen, dorsal view; 16) penis, lateral view; 17) penis, dorsal view. Scale bars: 9–11 = 1.0 mm; 12, 14–17 = 0.2 mm; 13 = 0.1 mm.