Geostiba (Sibiota) impressula ( Casey, 1906 )

Gusarov, Vladimir I., 2002, A revision of Nearctic species of the genus Geostiba Thomson, 1858 (Coleoptera: Staphylinidae: Aleocharinae), Zootaxa 81, pp. 1-88 : 68-72

publication ID

https://doi.org/ 10.5281/zenodo.155701

DOI

https://doi.org/10.5281/zenodo.6277585

persistent identifier

https://treatment.plazi.org/id/5B50E916-FFDD-3964-4D2D-FA62FCBDFCCC

treatment provided by

Plazi

scientific name

Geostiba (Sibiota) impressula ( Casey, 1906 )
status

 

13. Geostiba (Sibiota) impressula ( Casey, 1906) View in CoL , sp. propr. ( Figs. 306­320 View FIGURES 306 ­ 309 View FIGURES 310 ­ 315 View FIGURES 316 ­ 320 )

Sibiota impressula Casey, 1906: 350 View in CoL .

Sipalia fossata Casey, 1910: 167 View in CoL , syn. nov.

Sipalia View in CoL (s. str.) impressula: Fenyes, 1920: 251 View in CoL (as valid species).

Sipalia View in CoL (s. str.) fossata: Fenyes, 1920: 251 (as valid species).

Sipalia View in CoL (s. str.) impressula: Bernhauer & Scheerpeltz, 1926: 601 View in CoL (as valid species).

Sipalia View in CoL (s. str.) fossata: Bernhauer & Scheerpeltz, 1926: 601 (as valid species).

Sibiota impressula: Seevers, 1978: 262 View in CoL (as valid species).

Sibiota fossata: Seevers, 1978: 262 (as valid species).

Geostiba impressula: Lohse & Smetana, 1988: 270 View in CoL (as synonym of Geostiba circellaris (Gravenhorst) View in CoL ; misidentification).

Geostiba fossata: Lohse & Smetana, 1988: 270 View in CoL (as valid species).

Type material. Holotype of Sibiota impressula ,, “Portland, Oreg.[on]”, “ Sibiota impressula Csy. ”, “Casey bequest 1925”, “ TYPE USNM 39028” ( NMNH).

Lectotype of Sipalia fossata (here designated),, “Lane Co., Or.[egon]”, “ fossata Csy. ”, “Casey bequest 1925”, “ TYPE USNM 39029” ( NMNH). The purpose of the lectotype designation is to assure correct and consistent application of the name in the future.

Additional material. UNITED STATES: Oregon:, Portland [45.5°N 122.7°W] (Wickham) ( CASC);, 2, without locality data (Koebele) ( CASC); Lane Co.: 17 specimens, Triangle Lake [44°10’N 123°35’W, 200­250 m], leaf litter (I.M.Newell), 13.iv.1947 ( AMNH, KSEM, SPSU).

Diagnosis. Geostiba impressula can be distinguished from other Nearctic species of Geostiba by having large eyes (temple length to eye length ratio 1.8­2.5), pronotal pubescence of type VI, reduced wings, short elytra (pronotum length to elytron length ratio 1.3), the presence of two short parallel carinae in the middle of male abdominal tergum 7 in front of posterior margin, the shape of the aedeagus ( Figs. 310­315 View FIGURES 310 ­ 315 , 318­319 View FIGURES 316 ­ 320 ) and the shape of the spermatheca ( Figs. 316­317 View FIGURES 316 ­ 320 ).

Geostiba impressula differs from G. silvigena , another western Nearctic species, in having pronotal pubescence of type VI, reduced wings, shorter elytra, elytral suture behind scutellum flat, strong medial pronotal impression in males, larger aedeagus with the broader apex of the median lobe (in ventral view) ( Figs. 310­312, 315 View FIGURES 310 ­ 315 , 323­324 View FIGURES 321 ­ 326 ).

Description. Length 2.2­2.7 mm. Body reddish brown, sometimes with darker head and abdomen, antennae, legs and mouthparts brownish yellow. Body parallel­sided.

Head as wide as long, surface on disk with fine isodiametric microsculpture, puncturation very fine and weak, distance between punctures equal to 2­4 times their diameter. Temple length to eye length ratio 1.8­2.5. Antennal article 2 longer than article 3, article 4 slightly transverse (width to length ratio 1.2), articles 5­10 transverse (ratio 1.5­1.6), last article as long as 9 and 10 combined ( Fig. 16 View FIGURES 8 ­ 17 ).

Pronotum slightly transverse, width 0.37­0.50 mm, width to length ratio 1.0­1.1, wider than head (pronotal width to head width ratio 1.2); microsculpture and puncturation as on head. Pronotal pubescence of type VI. Elytra measured from humeral angle shorter than pronotum (pronotal length to elytral length ratio 1.3), wider than long (1.5), glossy, with traces of weak and fine isodiametric microsculpture and fine asperate puncturation, distance between punctures equals 2­3 times their diameter. Elytral suture not raised behind scutellum. 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 3­6 times their diameter. Tergum 7 without white edge.

Males with strong, wide and deep impression along midline of pronotum, the impression becomes deeper and wider posteriorly. In females pronotum flattened along midline. Male tergum 7 with two medial carinae in front of posterior margin. Male tergum 8 with four small carinae in front of posterior margin, posterior margin slightly convex, the carinae protruding posteriorly as four denticles ( Fig. 306 View FIGURES 306 ­ 309 ). Male sternum 8 with convex posterior margin ( Fig. 307 View FIGURES 306 ­ 309 ).

Posterior margin of female tergum 8 convex ( Fig. 308 View FIGURES 306 ­ 309 ). Posterior margin of female sternum 8 slightly concave medially ( Fig. 309 View FIGURES 306 ­ 309 ).

Aedeagus as in Figs. 310­315 View FIGURES 310 ­ 315 , 318­320 View FIGURES 316 ­ 320 . Apex of median lobe in lateral view bent ventrally ( Figs. 312­313 View FIGURES 310 ­ 315 ), in ventral view apex outline slightly emarginate basally ( Figs. 311, 315 View FIGURES 310 ­ 315 ).

Spermatheca as in Figs. 316­317 View FIGURES 316 ­ 320 .

Discussion. Lohse and Smetana (1988) examined the holotype of this species without studying the genitalia and placed G. impressula in synonymy with G. circellaris . My examination of the spermatheca of the holotype of G. impressula demonstrates that it has a very different shape in comparison to that of G. circellaris . The difference between the males of G. impressula and G. circellaris in the secondary characters and the shape of genitalia is even more significant. Geostiba impressula is therefore a valid species and it is removed from the synonymy with G. circellaris .

The type series of Sibiota impressula and Sipalia fossata are represented by a single specimen each, a female and a male, respectively. Because of the sexual dimorphism comparison between these two types alone would not allow to confirm their conspecificity. Fortunately, the big series of specimens from Triangle Lake includes both sexes and both types are identical to these specimens in external characters and genitalia. This allows to synonymize the two names.

Distribution. Known from Portland and the Cost Ranges in western Oregon ( Fig. 336 View FIGURE 336 ).

Natural History. Geostiba impressula was collected in forest litter at altitudes up to 250 m.

In June, 2002, I tried in vain to collect additional specimens of this species around Portland and in different localities throughout Oregon, from sea level to 1650 m. The dates and localities provided on the labels of examined specimens of G. impressula (April 13; 200­250 m) and G. silvigena (October 1; near sea level), along with the absence of Geostiba specimens in extensive collections made by different staphylinid specialists in summer months seem to indicate that the western Nearctic species of Geostiba are active only during the cooler and wetter time of the year.

USNM

Smithsonian Institution, National Museum of Natural History

NMNH

Smithsonian Institution, National Museum of Natural History

AMNH

American Museum of Natural History

Kingdom

Animalia

Phylum

Arthropoda

Class

Insecta

Order

Coleoptera

Family

Staphylinidae

SubFamily

Aleocharinae

Genus

Geostiba

SubGenus

Sibiota

Loc

Geostiba (Sibiota) impressula ( Casey, 1906 )

Gusarov, Vladimir I. 2002
2002
Loc

Geostiba impressula:

Lohse 1988: 270
1988
Loc

Geostiba fossata:

Lohse 1988: 270
1988
Loc

Sibiota impressula:

Seevers 1978: 262
1978
Loc

Sibiota fossata:

Seevers 1978: 262
1978
Loc

Sipalia

Bernhauer 1926: 601
1926
Loc

Sipalia

Bernhauer 1926: 601
1926
Loc

Sipalia

Fenyes 1920: 251
1920
Loc

Sipalia

Fenyes 1920: 251
1920
Loc

Sipalia fossata

Casey 1910: 167
1910
Loc

Sibiota impressula

Casey 1906: 350
1906
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