Lathrobium (s.str.) generosum, Ryvkin, 2011

Ryvkin, Alexandr B., 2011, On new and poorly known Lathrobium (s. str.) species from Siberia and the Russian Far East (Insecta: Coleoptera: Staphylinidae: Paederinae), Baltic Journal of Coleopterology 11 (2), pp. 135-170 : 150-152

Lathrobium (s.str.) generosum sp.n.

( Figs. 1–4 )

Material. 1 male-HT( ZMMU): “E Siberia, Irkutsk Area, right | side of Nizhnyaya Tunguska River near mouth | of Yuktakon River , 2 km below | Yerbogachen , swampy side | of flood-plain lake with Carex | acuta , C. rostrata , Acorus calamus | about 400 m off Nizhnyaya Tunguska River . | 18, 26.08.2008. [A.]Shavrin, [I.]Enushchenko [leg.]” [In Russian], “ HOLOTYPUS ”[my standard printed red label], “ Lathrobium HT | generosum sp. n. | A.B.Ryvkin det. 2008” [my standard determinative label].—1 male-PT( AR): together with holotype, “ PARATYPUS ”[my standard printed red label], “ Lathrobium | generosum sp. n. | A.B.Ryvkin det. 2008” [my standard determinative label].— 2 females ( AR): together with holotype, [immature females not included into the type series] .

Description. Body (in mature specimens) black to pitchy-black; elytra in posterior half more or less lighter, dark pitchy-brown to reddish-brown,

On new and poorly known Lathrobium (s.str.) species from Siberia and the Russian Far East ...

without distinct colour delimitation; antennae and labrum brown, mandibles brown to dark brown, maxillar palpi and legs brownish-yellow. Forebody distinctly, the fore abdominal tergites fatty shining. Pubescence fairly long and dense, piceous with golden shine.

Length: 9.5–9.6 mm (with abdomen extended).

Head about as long from neck to anterior margin of front as broad across basal 1/3 (82:81), nearly twice as broad as the neck constriction (81:43); posterior angles broad rounded, effaced, posterior margin straight in the middle; temples slightly convex, more than 3 times as long as eyes (48:15, view from above). Puncturation moderately deep and dense, irregular, much sparser medially, denser anterolaterally and laterobasally; average diameter of the coarsest punctures of the disk about equal to 1/3 cross-section of antennal segment 2; wide interstices between median punctures 2 to 3 times as broad as diameter of punctures; puncturation of temples much finer but denser than that on the disk; the underside punctured rather sparsely and shallowly. Small and close wavy-cellular ground-sculpture visible throughout; less evident, extremely fine on median area of the disk. Antennae fairly long, reaching the basal margin of pronotum, with segments 2–10 inverted conical. Length/width proportions of antennal segments 1–11 as 29/12: 15/10: 18/10: 15/10: 15/10: 15/10: 16/11: 15/11: 16/11: 15/11: 22/10.

Pronotum moderately convex, nearly as broad as head (80:81), by more than 1/5 longer than broad (98:80); lateral sides subparallel (79:80:77); anterior angles angularly, posterior ones broadly rounded; very fine median longitudinal furrow well developed in basal 1/5, more or less distinctly extending as a feeble stroke to the middle of length. Median longitudinal impunctate strip reaching both anterior margin and posterior one, slightly raised in basal part, as broad as 1/10 maximum breadth of pronotum. Puncturation of disk irregular, evidently larger on average than that of head; interstices between punctures near the smooth longitudinal median strip on average evidently smaller than the diameter of punctures.

Ground-sculpture almost absent, only extremely small and vague punctures and scratches visible at high magnification.

Elytra moderately convex, rather long and wide, by nearly 1/6 longer than pronotum (115: 98 in holotype), markedly longer than broad (115:97), slightly dilated posteriorly (89:97) behind well developed angularly-rounded humeri. Suture a little shorter than pronotum (92: 98 in holotype), somewhat elevated throughout excluding the very base; flanked with a pair of narrow and shallow sutural impressions; humeral and lateral impressions absent; posterior margin with extremely fine edging visible only in external parts. Puncturation evidently smaller and more regular than that of pronotum, average diameter of punctures on the disk about equal to that on the head. Very shallow irregular point-touch ground-sculpture more or less evident between punctures at high magnification. Winged.

Abdomen uniformly and weakly widened posteriorly, segments 6–7 slightly broader than fore visible segments; abdominal tergites evidently flattened, preapical tergites more convex. Posterior margin of tergite 7 with evident white fringe. Puncturation of fore visible abdominal tergites rather uniform, very fine and dense, somewhat sparser medially; tergites 7–9 punctated much more sparsely. Extremely fine and dense reticular ground-sculpture well-developed throughout but much more feeble on preapical tergites.

Male: Medioposterior emargination of abdominal sternite 8 nearly symmetric, moderately broad and deep angularly rounded; spicule rows on the sternite 8 about as in L. geminum Kraatz , but somewhat shorter owing to the developed emargination of posterior margin (fig. 4); aedeagus as in figs. 1–3.

Female: No mature material available.

Etymology. The specific name is the Latin adjective “generosum ” (well-born, thoroughbred, pedigree).

Ryvkin A.B.

Diagnosis. In the shape of the aedeagus, this species is closely related to L. geminum Kraatz, 1857 and differs from the typical form of the latter by the darker colour of elytra, the somewhat narrower neck, the body proportions a bit more slender, the antennae a bit more thick, the somewhat finer and denser head puncturation, the broad-angularly emarginated male abdominal sternite 8 (compare figs. 4 and 7), and the details of structure of the aedeagus (compare figs. 1–3 and 5–6). It can be distinguished from L. dimidiatipenne Bernhauer, 1910 , also found in terra typica of the new species, by the darker colour of elytra, the body proportions somewhat more robust, the more angular emargination of male abdominal sternite 8, and the details of structure of the aedeagus.

Remarks. This unexpected new species seems to be a derivative of L. geminum Kraatz (see above). It arose likely from an isolation of the local population near the border of the range.

Figures

Figures 1–7. ― Male structures of Lathrobium spp. 1–4. L. generosum sp.n. (1–2: HT, 3–4: PT): aedeagus (1: apical part laterally, 3: laterally, 2: operculum from the side opposite to the basal opening), abdominal sternite 8 ventrally (4). 5–7. L. geminum Kraatz, 1857. (Tyumen Area:Mazurovo): aedeagus (5: apical part laterally, 6: operculum from the side opposite to the basal opening), abdominal sternite 8 ventrally (7). The long axes of spicule rows in the male abdominal sternites are shown as dash-lines. Scale = 0.1 mm.