Stylogymnusa subantarctica

Introduction

The single species of Stylogymnusa, S. subantarctica, is light brown, flightless with greatly shortened elytra, has greatly reduced eyes, and is 3.8-4.6 millimeters in length.

Specimens of S. subantarctica are very rare, and details of the habitat of this species are not known. However, Hammond (1975) noted that other members of the Gymnusini and the closely related Deinopsini are found in swampy, marshy or other riparian situations. He pointed out that swampy and marshy habitats are abundant on the Auckland Islands, and label data indicate that specimens have been collected from litter in bogs and swamps. However, the reduction of eyes of S. subantarctica is extreme, and Hammond speculated that the species inhabits the deepest layers of litter, or it could be subterranean.

Stylogymnusa subantarctica is only known from the subantarctic Auckland Islands, and probably represents a relict species from the time when Gymnusini were more widespread and diverse.

Hammond (1975) first proposed the sister group relationship between Gymnusa and Stylogymnusa. He provides a detailed description and illustrations of diagnostic features of Stylogymnusa.

Characteristics

Adults of Stylogymnusa can be distinguished from Gymnusa by presence in Stylogymnusa of:

• very minute eyes;
• elongate labrum (greater than 2 times as long as wide);
• inner margin of mandible with 2 large and 4-5 small subapical teeth;
• elongate basal segment of maxillary palpus (almost as long as segment II);
• outer posterior angle of elytra not emarginate;
• pectinate posterior margin of abdominal segments III-V with 2 distinct kinds of teeth (acutely pointed teeth alternating with apically rounded teeth)

(Klimaszewski 1979, 1982).

Ashe (2000) provides detailed discussion and reinterpretation of the structure of Stylogymnusa, and illustrations of mouthparts, within the context of a comparison with Gymnusa.

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Mouthparts of S. subantarctica, from left to right, mandible, maxilla detail, maxilla, labrum, labium and mentum, and detail of apex of labial palpus (redrawn from Ashe 2000).

Other Names for Stylogymnusa subantarctica

• Stylogymnusa

References

Ashe, J. S. 2000. Mouthpart structure of Stylogymnusa subantartica Hammond, 1975 (Coleoptera: Staphylinidae: Aleocharinae) with a reanalysis of the phylogenetic position of the genus. Zoological journal of the Linnean Society 130: 471-498.

Hammond, P. 1975. The phylogeny of a remarkable new genus and species of gymnusine staphylinid (Coleoptera) from the Auckland Islands. Journal of Entomology (B) 44(2): 153-173.

Klimaszewski, J. 1979. A revision of the Gymnusini and Deinopsini of the World. Canada Agriculture monograph No. 25. 169 pp.

Klimaszeski, J. 1982. A revision of the Gymnusini and Deinopsini of the world. Sup. 2. Canadian Entomologist 114: 317-335.