Geostiba

15. Geostiba (s. str.) circellaris (Gravenhorst, 1806) (Figs. 21­23; Figs. 1­4 in Assing (2001))

Aleochara circellaris Gravenhorst, 1806: 155.

Geostiba (s. str.) circellaris: Benick & Lohse 1974: 112. Geostiba circellaris: Muona 1984: 229.

Geostiba (s. str.) circellaris: Assing 2001: 139.

Material. CANADA: Newfoundland:,, S Newfoundland, Rencontre West [47.61°N 56.69°W] (Lindroth), 16.vi.1949 (MZHF).

Diagnosis. Geostiba circellaris can be distinguished from other Nearctic species of Geostiba by having large eyes (temple length to eye length ratio 1.6­1.9), pronotal pubescence of type VI, reduced wings, elytra shorter than pronotum (pronotum length to elytron length ratio 1.1), the presence of one medial carina on male abdominal tergum 7 in front of posterior margin, the shape of the aedeagus and spermatheca (Figs. 1­4 in Assing (2001), Figs. 21­23).

In North America there is no native species closely related to G. circellaris. Geostiba circellaris is superficially similar to G. impressula in having pronotal pubescence of type VI but can be distinguished from the latter species by having tergum 7 with one medial carina in males and a different shape of spermatheca in females (Fig. 4 in Assing (2001), Figs. 316­317).

Description. Length 2.3­2.8 mm. Body reddish brown to brownish black, in some specimens pronotum, elytra and abdominal segments 7­8 lighter, antennae reddish brown to dark brown, legs and mouthparts from brownish yellow to brown. Body parallel­sided.

Head as wide as long, surface on disk with fine isodiametric microsculpture, puncturation very fine, distance between punctures equal to 2­4 times their diameter. Temple length to eye length ratio 1.6­1.9. Antennal article 2 longer than article 3, article 4 subquadrate, articles 5­10 transverse, last article longer than 9 and 10 combined.

Pronotum as wide as long, width 0.43­0.53 mm, wider than head (pronotal width to head width ratio 1.2); surface on disk with fine isodiametric microsculpture, and fine puncturation, distance between punctures equal to 1­2 times their diameter; pronotal pubescence of type VI. Elytra measured from humeral angle shorter than pronotum (pronotal length to elytral length ratio 1.1), wider than long (1.4), with fine isodiametric microsculpture and fine asperate puncturation, punctures stronger than on pronotum, distance between punctures equals 1­2 times their diameter.

Abdominal terga with fine transverse microsculpture, with fine puncturation, puncturation becoming finer towards abdomen apex, on terga 3­5 distance between punctures equals 2­4 times their diameter. Tergum 7 with white edge.

In males pronotum with small medial tubercle at posterior margin (some females have very weak tubercle) and medial impression in front, each elytron with a tubercle near scutellum but distant from elytral suture. Male tergum 7 with one short medial carina in front of posterior margin. Male tergum 8 with two weak and short parallel carina in front of middle of convex posterior margin. Male sternum 8 with posterior margin convex, extending posteriorly beyond tergum.

Aedeagus as in Figs. 1­3 in Assing (2001). Internal sac of aedeagus with one pair of large diverticula (Figs. 21­22).

Posterior margin of female tergum 8 convex. Posterior margin of female sternum 8 distinctly convex, without emargination.

Spermatheca as in Fig. 4 in Assing (2001).

Distribution. Geostiba circellaris is a widespread Palaearctic species. In the Nearctic region, it is known only from Newfoundland (Muona 1984), where it was introduced from Europe. Contrary to the opinion expressed by Lohse and Smetana (1988) Geostiba impressula (Casey, 1906) is not a synonym of G. circellaris (see discussion for G. impressula). Geostiba circellaris is not known from western North America.