Stenus (Nestus) pluvius, Ryvkin, 2014

Ryvkin, Alexandr B., 2014, Stenus (Nestus) Pluvius Sp. N., With Notes On Some Related Species (Coleoptera: Staphylinidae: Steninae), Acta Biologica Universitatis Daugavpiliensis 14 (2), pp. 187-205 : 188-191

Stenus (Nestus) pluvius sp. n.

(Figs. 1–3, 7)

Material examined. 1 male-HT ( ZMMU): ‘ Amur Area, Selemdzhinskiy | District, Norskiy Nature Reserve, | Selemdzha River basin near | Burundushka River mouth, clayish | and sandy-clayish river | banks [with Carex spp. , Poaceae , Salix spp. , Equisetum spp. , etc]. 03.08.2004. A.B.Ryvkin leg. #3’<in Russian>;‘HOLOTYPUS’<my standard printed red label>;‘ Stenus HT | pluvius sp. n. | A.B. Ryvkin det. 2004’<my standard determinative label>.—1 male-PT ( AR), 1 male-PT ( IRSN): ‘ Amur Area, Selemdzhinskiy | District, near border of Norskiy | Reserve, island on | Selemdzha River near Dvadtsatikha | cordon, leaf litter, moss and drift in the heart of the island |[: among Salix spp. , Populus sp. , Picea ajanensis , Abies nephrolepis , Alnus sp. , Larix gmelinii with Poaceae , Carex sp. , etc]. 06.08.2004. A.B.Ryvkin leg. #11’<in Russian>.—3 males-PTT, 7 females-PTT ( AR), 1 male-PT, 1 female-PT ( MHNG): ‘ Amur Area, Selemdzhinskiy | District, Norskiy Nature Reserve [(buffer zone)],| Burunda River, 1 km below Burunda | cordon, mosses [( Plagiomnium Fig. 1–6. ― Male copulative structures of Stenus (Nestus) spp. 1, 6: Aedeagus, ventral view. 2, 4–5: Apical part of aedeagus, ventral view. 3: Abdominal sternite 9. 1–3: S. (N.) pluvius sp.n. ( HT). 4: S. (N.) incautus Ryvkin, 2000 (Samara Area). 5. S. (N.) lohsei Puthz, 1965 (Isonzo). 6. S. (N.) immodicus Ryvkin, 2000 (Bol’shekhekhtsyrskiy Nature Reserve). Scale = 0.1 mm. sp. etc.)] and leaf litter under | Salix sp. with sparse Poaceae , | Carex sp. , [ Filipendula palmata , Pyrola sp. ,] etc. along base | of shinglesandy spit. | 25.09.2004. A.B.Ryvkin leg.’ <in Russian>.<in Russian>.— 1 female ( AR): Amur Area, Selemdzhinskiy District, Norskiy Nature Reserve, Burunda River near Ozyornyi Rill mouth, mosses and leaf litter under Salix sp. and Alnus sp. with separate tussocks of Carex sp. , Plagiomnium sp. , etc. on flood-plain (near old channel). 30.09.2004. A.B.Ryvkin leg.

The paratypes listed above are also provided with both ‘PARATYPUS’ printed red label and my standard determinative label (‘ Stenus | pluvius sp. n. | A.B. Ryvkin det., 2004’) for each lot.

Description. Pitchy black, moderately fatty shining, moderately densely punctured, with not long but fairly dense yellowish-silvery pubescence. Antennae brown, with basal segment brownish-black, segments of club dark brown; palpi brown with 1 st segment and the very base of the 2 nd yellow; legs brown to reddish-brown, knees slightly infuscate; labrum pitchy-black to pitchy-brown, moderately pubescent with yellowish-silvery hairs.

Length: 2.7–2.9 mm (the last value with extended abdomen).

Head by nearly 1/4 th broader than pronotum (41:33, all measurements are from the holotype), a scarcely broader than elytra between humeri (41:40) and somewhat narrower than in their broadest part (41:45). Front with two shallow but evident longitudinal impressions; medial elevation broad and prominent, posteriorly more than twice as broad as lateral portions (13:5). Puncturation moderately coarse and dense, irregular, partly confluent but not rugose; the greatest punctures are nearly as large as the broadest section of 3rd antennal segment; median elevation of the front vith longitidinal strip impunctate distinctly broader than average diameter of punctures. Length proportions of antennal segments 2–9 as 5:6:5:4.5:4:4:3:3; segments 9–10 good as broad as long each; segment 11 twice as long as broad. Antennae scarcely reaching posterior quarter of pronotum.

Pronotum moderately convex, a bit longer than broad (34:33), broadest near middle, narrowed feebly convexly towards anterior margin and concavely towards posterior one, without distinct furrows and impressions. Puncturation of the disk somewhat greater and more regular than that of the head, partly nonrugosely confluent.

Elytra good as broad as long (45:45), somewhat dilatedposteriorlybehindevidenthumeri(40:45), much longer than pronotum (45:34), at suture distinctly longer than the latter (38:34); sutural impression very feeble, humeral impressions short and vague. Puncturation fairly dense and regular, slightly nonrugosely confluent only at sutural and humeral impressions, punctures evidently larger than that of pronotum, about as large as the cross-section of the 2nd antennal segment; interstices between punctures smaller than ½ average diameter of punctures.

Wings well developed.

Legs of moderate length; metatibia by more than 2/5 longer than metatarsus (36:25); segment 1 of metatarsi good as long as segment 5 (7:7).

Abdomen subcylindrical, distinctly narrowed posteriorly; with paratergites moderately developed at segments 3 to 4 and gradually narrowed to segment 7; anterior tergites with four short but developed longitudinal keels at their basal parts. Posterior margin of tergite 7 with fine light fringe. Puncturation of anterior visible tergites somewhat smaller and distinctly shallower than that of head, most dense at lateral parts, medially more distant.

Very fine and dense mesh-like ground sculpture well developed throughout but less evident on head and interstices between punctures along midline of anterior visible abdominal tergites.

Male. Meso- and metatibiae without any teeth; abdominal sternites 7–8 with neither emarginations nor impressions; posterior margin of 8 th abdominal sternite broad convexly rounded; 9 th abdominal sternite as in Fig.3; aedeagus as in Fig. 1–2.

Female. Abdominal sternite 8 with broad convexly rounded posterior margin. Spermatheca as in Fig.7.

Etymology. The name of the species is the Latin adjective “ pluvius ” (rainy).

Diagnosis. The species is externally very similar to S. rigidus Casey, 1884 and can be distinguished from all the known Stenus species by plain differences in the shape of the aedeagus and spermatheca (compare Figs.7–8) as well as by the absence of emarginations and impressions at both 7 th and 8 th male abdominal sternites. It differs from all the Far Eastern species of the cautus group by more developed ground sculpture of the forebody; from S. rigidus by the body somewhat more slender, and by the colour of legs on average lighter.

Remarks. As being closely related to S. rigidus Casey, 1884 , the new species must be included in the atratulus group which was mentioned formerly in some publications (e.g. Puthz 1971b) but was not properly diagnosed. This complex is now being inserted either in the argus group ( Ryvkin 1990) or in the crassus group (Puthz

Fig. 7–8. ― Spermatheca of Stenus (Nestus) spp. 7. S. (N.) pluvius sp.n. (PT). 8. S. (N.) ageus Casey, 1884 (Khabarovsk Territory). Scale = 0.1 mm.

2013a); though I suppose it to be a well defined independent group.