Stethusa Casey 1910
Creators: name: Gusarov, Vladimir I.
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Stethusa

description: Stethusa Casey, 1910
(Figs. 1­109)
Atheta (Stethusa Casey, 1910): 4 (type species: Atheta irvingi Casey, 1910, designated by Fenyes (1918)).
Atheta (Stethusa): Casey, 1911a: 77 (as valid subgenus).
Atheta (Stethusa): Fenyes, 1918: 25.
Atheta (Stethusa): Fenyes, 1920: 206 (as synonym of Atheta (Hypatheta Fenyes, 1918)).
Atheta (Stethusa): Bernhauer & Scheerpeltz, 1926: 652 (as synonym of Atheta (Hypatheta )).
Atheta (Stethusa): Moore & Legner, 1975: 353 (as valid subgenus).
Stethusa: Seevers, 1978: 125 (as valid genus in subtribe Xenotae Seevers, 1978 (nomen nudum )).
Stethusa: Ashe in Newton, Thayer, Ashe & Chandler, 2000: 369 (as valid genus in subtribe Athetina Casey, 1910).
Diagnosis. Stethusa is distinguished from other athetine genera by the combination of the following characters: body parallel­sided; anterior margin of labrum concave; sensilla a of epipharynx long; antennal article 2 slightly longer than article 3, articles 4­10 slightly elongate or subquadrate; ligula with narrow base and split apically (Fig. 8); labial palpus with setae, and present (Fig. 8); pronotum slightly transverse, 1.2 times as wide as long, with microsetae directed anteriorly along the midline; in lateral portions of the disc microsetae directed laterally (Type I, Benick & Lohse 1974) (Fig. 18); pronotal macrosetae long; pronotal hypomera fully visible in lateral view; medial macroseta of mesotibia thick and long, twice as long as tibial width (Fig. 14); mesothoracic process broad (Fig. 19­21); tarsal formula 4­5­5; metatarsal segment 1 as long as segment 2; one long empodial seta; abdominal terga 3­5 with transverse basal impression; medial lamellae of internal sac absent; copulatory piece with pointed apex (Figs. 34, 36, 56) and sclerotized suspensoria (Figs. 36, 56); medial lamellae absent; internal sac with two sclerotized bands (Figs. 34, 38, 54) which change their orientation when the sac everts; spermatheca short (Figs. 41­42, 57).
Stethusa is distinguished from Atheta (including Dimetrota auct.) by a broader mesothoracic process (Figs. 19­21); the lack of the median lamellae of the internal sac; the distinct shape of the copulatory piece (Figs. 36, 39, 55­56); and a short spermatheca (Figs. 41­42, 57).
Stethusa differs from Earota Mulsant & Rey, 1874 in having sensilla a of the epipharynx long; pronotal setation of type I; slightly narrower mesothoracic process; by the lack of the median lamellae of the internal sac; and the distinct shape of the copulatory piece (Figs. 36, 39, 55­56).
Description. Length 2.0­ 3.5 mm, pronotal width 0.46­0.77 mm. Body parallel­sided. Body brown to dark brown, with brownish yellow elytra and yellow legs.
Head transverse; eyes very large, eye length to temple length ratio 2.5­5; infraorbital carina complete. Antennal article 2 slightly longer than article 3, articles 4­10 slightly elongate, subquadrate or transverse, apical article without coeloconic sensilla (not to be mixed with subbasal impression densely covered with microsetae, present in S. dichroa and S. luederwaldti), as long as or longer than articles 9 and 10 combined. Labrum (Fig. 1) transverse, with concave anterior margin. Epipharynx (Figs. 2, 6) with long sensilla a, with three pairs of small marginal setae, medial field with 36­38 pores, lateral rows with three pores each, anterolateral groups with three to four pores each, transverse row with six pores, posterolateral groups with four pores each, with one medial proximal pore on each side and no lateral proximal pores. Mandibles (Figs. 3­5) broad, right mandible with a small medial tooth; dorsal molar area with velvety patch consisting of very small denticles (poorly visible at 400x). Maxilla (Figs. 9­12) with galea projecting slightly beyond apex of lacinia; apical lobe of galea covered with numerous fine and short setae; internal margin of galea with long subapical setae (Fig. 12); distal comb of lacinia is divided into isolated groups of 6 and 2 closely placed spines (Figs. 10­11), middle portion produced medially and covered with numerous fine setae (Figs. 10­11), ventral surface of lacinia with a medial group of 4 strong setae and marginal group of 5 strong setae (Fig. 10), dorsal surface of lacinia with a row of 13 strong setae (Fig. 11). Labium as in Figs. 7­8, 13; ligula with narrow base and split apically (Fig. 8); medial area of prementum with 2 pores and with 8­20 pseudopores, lateral areas each with two asetose pores, single setose pore and 8­ 12 pseudopores (Fig. 8). Hypopharyngeal lobes as in Fig. 7. Labial palpus with setae,, and present (Fig. 8). Mentum (Fig. 13) with concave anterior margin.
Pronotum (Fig. 18) slightly transverse, 1.2 times as wide as long, with microsetae directed anteriorly in midline; in lateral portions of disc microsetae directed laterally (Type I, Benick & Lohse 1974); macrosetae short; hypomera fully visible in lateral view. Meso­ and metasternum as in Figs. 19­21, mesosternal process moderately wide, extending about ½ length of mesocoxal cavities, metasternal process short, mesosternum and mesosternal process not carinate medially or (in S. dichroa) mesosternum with very short carina (Fig. 19); relative lengths of mesosternal process: isthmus: metasternal process in ratio of about 3:1:2 or 4:1:2; mesocoxal cavities margined posteriorly; mesocoxae moderately widely separated. Medial macroseta of mesotibia long and thick, twice as long as tibial width. Tarsal segmentation 4­5­5, metatarsal segment 1 as long as segment 2. One empodial seta, shorter than claws. Posterior margin of elytra straight. Wings fully developed.
Abdominal terga 3­5 with moderate basal impressions. Tergum 7 is 1.1 times as long as tergum 6. Punctation on terga 6­7 sparser than on terga 3­5. Tergum 7 with wide white palisade fringe.
Internal sac of aedeagus without medial lamellae; with two sclerotized bands (which may be homologous to medial lamellae; however, unlike the medial lamellae the distal end of the bands is oriented towards the base of median lobe in retracted internal sac); copulatory piece with pointed apex (Figs. 34, 36, 56) and sclerotized suspensoria (Figs. 36, 56), in lateral view curved (Figs. 37, 39); spermatheca short (Figs. 41­42, 57).
Type species. Atheta irvingi Casey, 1910, by subsequent designation (Fenyes, 1918).
Discussion. When describing Stethusa, Casey (1910) did not explicitly fix the type species of the subgenus. While designating the type species of Noverota Casey, 1910 in the same paper, Casey stated (1910, p. 90): “The first species may be regarded as the type, as in all other cases where the type is not specifically named”. Unfortunately it is not clear how to apply this recommendation to Stethusa. The first species described by Casey in Stethusa is At. affluens Casey, 1910. However, before Casey proceeds to describing the new species he mentions that Stethusa includes many allies of At. klimschi Bernhauer, 1909; therefore, At. klimschi was also a species originally included in Stethusa. Because it is not clear which of the two species, At. klimschi or At. affluens qualifies as the type species under Casey's first species rule, I maintain that Casey has not validly fixed the type species of Stethusa.
Fenyes (1920) listed the subgenus Stethusa as a synonym of the subgenus Hypatheta Fenyes, 1918 and included the type species of Stethusa in Hypatheta. The type species of Hypatheta is Atheta castanoptera (Mannerheim, 1830), currently placed in Atheta s. str. Atheta castanoptera and other related species of the subgenus Atheta s. str. differ from Stethusa in having a narrow mesosternal process, a long spermatheca of distinct shape with a thick distal portion and a thin proximal portion and by the presence of medial lamellae of the internal sac.
Seevers (1978) raised Stethusa to generic rank. The only character listed in the diagnosis of the genus (p. 125) is the oval pale areas near the base of the terminal antennal segment. Seevers noted that S. klimschi (Bernhauer, 1909) lacks this feature but retained it in Stethusa. In the key to genera (p. 51) another diagnostic character of Stethusa is mentioned, the broad mesosternal process.
Ashe (Newton et al. 2000) followed Seevers (1978) and mentioned that thirteen species belong to Stethusa. In the key to genera (pp. 317, 319) "a subbasal "spongy" sensory patch on each side" of the terminal antennal segment is the only mentioned diagnostic character of the genus.
My examination of the antennae of S. dichroa at high magnification (400x) demonstrated that in this species the terminal antennal article has two subbasal impressions (Fig. 16). The microsetae in these impressions are denser and wider, somewhat scale­like, compared to microsetae covering the rest of the article (Fig. 15). All species of Stethusa described by Casey (1910, 1911a) that possessed this modification of the terminal antennal article turned out to be synonyms of S. dichroa (see below). Two other valid Nearctic species of Stethusa, S. klimschi and S. spuriella, lack the basal impressions of the last antennal segment. Therefore, this feature is not considered here a diagnostic character of the genus Stethusa.
Based on the differences between Stethusa and Atheta listed in the Diagnosis, both are considered here as valid genera, pending a revision of the genera of Athetini.
description: Published as part of Gusarov, Vladimir I., 2003, A revision of the Nearctic species of the genus Stethusa Casey, 1910 (Coleoptera: Staphylinidae: Aleocharinae), pp. 1-43 in Zootaxa 239 on pages 5-11, DOI: 10.5281/zenodo.156493