Geostiba (Sibiota) crepusculigena Gusarov,

Gusarov, Vladimir I., 2002, A revision of Nearctic species of the genus Geostiba Thomson, 1858 (Coleoptera: Staphylinidae: Aleocharinae), Zootaxa 81, pp. 1-88: 44-46

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Geostiba (Sibiota) crepusculigena Gusarov


7. Geostiba (Sibiota) crepusculigena Gusarov  , sp. n. ( Figs. 169­186View FIGURES 169 ­ 173View FIGURES 174 ­ 177View FIGURES 178 ­ 186)

Type material. Holotype ,, UNITED STATES: Tennessee: Cocke Co.: Snake Den Ridge Trail, 9 km S Cosby, 35 ° 44.18 'N 83 ° 14.60 'W, 1520 m, in forest litter, Picea  , Rhododendron  , Betula  (V.I.Gusarov), 23.ix. 2001 ( KSEM).

Paratypes: UNITED STATES: Tennessee: Cocke Co.: 20 specimens, same data as the holotype; 10 specimens, ditto but 8 km S Cosby, 35 ° 44.61 'N 83 °14.00'W, 1470 m, Tsuga  , Picea  , Rhododendron  , Betula  (all – KSEM, SPSU).

Diagnosis. Geostiba crepusculigena  can be distinguished from other Nearctic species of Geostiba  by having small eyes (temple length to eye length ratio 3.0­ 3.1), pronotal pubescence of type V, reduced wings, short elytra (pronotum length to elytron length ratio 1.3), the presence of two short parallel carinae in the middle of abdominal tergum 7 in front of posterior margin, the shape of the aedeagus ( Figs. 174­180, 182 ­ 186View FIGURES 174 ­ 177View FIGURES 178 ­ 186) and the shape of the spermatheca ( Fig. 181View FIGURES 178 ­ 186).

Geostiba crepusculigena  differs from closely related G. nimbicola  , G. pluvigena  and G. nebuligena  in having apex of median lobe with obtuse apical projection (in lateral view) ( Figs. 176­177View FIGURES 174 ­ 177, 102­ 103View FIGURES 100 ­ 107, 128­129View FIGURES 126 ­ 133, 155­ 156View FIGURES 152 ­ 156).

Description. Length 1.8­2.3 mm. Body brown to dark brown, antennae brown, legs and mouthparts brownish yellow. Body parallel­sided.

Head as wide as long, surface on disk with fine isodiametric microsculpture, puncturation very fine, distance between punctures equal to 3­4 times their diameter. Temple length to eye length ratio 3.0­ 3.1. Antennal article 2 longer than article 3, article 4 transverse (width to length ratio 1.6), articles 5­10 strongly transverse, last article as long as 9 and 10 combined (as in Fig. 17View FIGURES 8 ­ 17).

Pronotum as wide as long, width 0.34­0.40 mm, wider than head (pronotal width to head width ratio 1.1); microsculpture and puncturation as on head. Pronotal pubescence of type V. Elytra measured from humeral angle shorter than pronotum (pronotal length to elytral length ratio 1.3), wider than long (1.5), with fine isodiametric microsculpture and fine asperate puncturation, distance between punctures equals 1­3 times their diameter. Elytral suture behind scutellum slightly raised in both sexes. Wings reduced to short vestiges, shorter than elytra.

Abdominal terga with fine microsculpture of transverse meshes, with fine and sparse puncturation, puncturation becoming finer towards abdomen apex, on terga 3­5 distance between punctures equals 2­6 times their diameter. Tergum 7 without white edge.

Male tergum 7 with two medial carinae in front of posterior margin. Male tergum 8 with two or four weak and short carinae in front of posterior margin, posterior margin convex ( Fig. 169View FIGURES 169 ­ 173). Male sternum 8 with convex posterior margin ( Fig. 170View FIGURES 169 ­ 173).

Female tergum 8 with convex posterior margin ( Fig. 171View FIGURES 169 ­ 173), sternum 8 with strongly emarginate posterior margin ( Figs. 172­173View FIGURES 169 ­ 173).

Aedeagus as in Figs. 174­180, 182 ­ 186View FIGURES 174 ­ 177View FIGURES 178 ­ 186. Apex of median lobe in ventral view narrow, its outline convex apically ( Figs. 174­175View FIGURES 174 ­ 177), in lateral view strait, with strong obtuse apical projection ventrally ( Figs. 176­177View FIGURES 174 ­ 177), distal diverticula of internal sac in ventral view broad ( Figs. 179­180View FIGURES 178 ­ 186).

Spermatheca as in Fig. 181View FIGURES 178 ­ 186.

Distribution. Known from Snake Den Mountain in the Great Smoky Mountains massif (Tennessee) ( Figs. 338View FIGURE 338, 340View FIGURE 340).

Natural History. Geostiba nebuligena  was collected at altitudes of 1400­1600 m in leaf litter in mixed forest with red spruce ( Picea rubens  ), birch, purple laurel ( Rhododendron catawbiense  ) and hemlock.

Etymology. The specific name is derived from the Latin noun crepusculum (dusk, twilight) and the verb gigno (to be born, to arise). It refers to the dark forests in the Great Smoky Mountains where the species occurs.