Rhopalomma Ashman, Oberprieler & Ślipiński, 2015

Ashman, Lauren G., Oberprieler, Rolf G. & Ślipiński, Adam, 2015, Rhopalomma stefaniae gen. et sp. n., the first ommatid beetle from the Upper Jurassic in Australia (Coleoptera: Archostemata: Ommatidae), Zootaxa 3980 (1), pp. 136-142 : 137-138

Rhopalomma Ashman, Oberprieler & Ślipiński gen. n.

Type species: Rhopalomma stefaniae Ashman, Oberprieler & Ślipiński sp. n.

Description. Body elongate-oval, 2.5 times longer than wide ( Figs. 1, 2 , 5, 6 ). Head slightly longer than wide; clypeus not distinctly separated from frons; short labrum indicated; antennae laterally inserted, 11-segmented, slightly shorter than head, last three antennomeres enlarged to form a slight club ( Fig. 4 ). Prothorax subquadrate; pronotum with anterior margin straight, posterior margin arcuate with distinct ridge ( Fig. 3 ). Prothoracic legs short, stout; femora broad, tibiae narrowly cylindrical. Scutellar shield small, subtriangular. Elytra flat dorsally, fairly abruptly sloping laterally, rounded apically, sides expanded into narrow, complete flanges of approximately uniform width; epipleura complete. Elytra clathrate, each with 10 complete striae of deep cell-like punctures extending from base to apex, and a scutellary striole with 3 punctures; striae 1–6 on disc, with approximately 30– 34 cells each, striae 7–10 on lateral slope; odd intervals 1, 3, 5 and 7 raised, almost as broad as strial punctures and twice as broad as even intervals; intervals 3 and 5 confluent before apex.

Etymology. The generic name is a combination of the Greek noun rhopalos (club, referring to the slightly clubbed antennae) and Omma (the type genus of the family) and its gender is feminine.

Remarks. We assign Rhopalomma to Archostemata based on several characters: the closely placed convex tubercles on the cuticular pieces of the pronotum, head and elytral margins; the complete epipleura; the ten striae of cell-like punctures on the elytra and the strongly developed scutellary strioles. Of the families of Archostemata, we place Rhopalomma in Ommatidae because of the relatively short antennae (not longer than the head and prothorax together) and their lateral insertion ( Crowson 1962; Lawrence & Ślipiński 2013).

Due to the poor preservation and incompleteness of the specimen, we cannot confidently assign Rhopalomma to a subfamily or tribe of Ommatidae , and therefore we classify it as Ommatidae incertae sedis. One key character distinguishing Ommatinae from the other two subfamilies ( Tetraphalerinae and Notocupedinae) is the absence of lateral carinae on the pronotum ( Crowson 1962; Tan et al. 2012); the lateral margins of the specimen’s pronotum are unclear, and hence we cannot use this character to undertake a further taxonomic placement. Furthermore, the crucial characters distinguishing Ommatinae from Tetraphalerinae , the presence of antennal grooves on the head and of protibial grooves on the propleura ( Crowson 1962), are not visible on the specimen. However, Rhopalomma is more likely to belong in Ommatinae than Tetraphalerinae , as its head does not have raised tubercles or ridges.

The pattern of the elytral striae of Rhopalomma is very similar to that of Notocupes Ponomarenko (and other Notocupedini), in that there are four prominent intervals on each elytron, with two striae of punctures in between, and the second and third prominent intervals are confluent before the elytral apex ( Jarzembowski et al. 2014). However, the clubbed antennae and the lack of a ‘neck’ region on the head are characters unique to Rhopalomma and merit placing the specimen in its own genus.

Figures

FIGURES 1 – 2. Rhopalomma stefaniae gen. et sp. n. 1. part (AM F. 139992); 2. counterpart (AM F. 139993). Scale bars are 1 mm.

FIGURES 5 – 6. Rhopalomma stefaniae gen. et sp. n. line drawings. 5. part (AM F. 139992); 6. counterpart (AM F. 139993).

FIGURES 3 – 4. Rhopalomma stefaniae gen. et sp. n., details of head and prothorax. 3. part (AM F. 139992); 4. counterpart (AM F. 139993), after further exposure of structures, with antennal club and pronotum labelled. Scale bars are 1 mm.