Hydraena biltoni (Fig. 3A) is endemic to Montenegro. Previously, it was collected from the vicinity of Šavnik, about 20 km south of Žabljak and Biogradska Gora (Jäch and Díaz 2012).

Figure 3.  

Digital habitus photograph of A) Hydraena biltoni ♂; B) H. minutissima ♂; C) H. morio ♀; D) H. nigrita ♂; E) H. subintegra, pale colouration of a teneral ♂ specimen; F) H. subintegra ♂, regular colouration; scale bar = 1.0 mm.

We provide the first standard barcode for the species. It varies by only 0.3% from that of the closest congener H. morio Kiesenwetter, 1849 (Suppl. material 1). As H. biltoni is extremely similar to the latter, which also occurs in the region, thorough examination of the aedeagus is required for proper identification.

The specimens were collected in a very small creek, flowing through pine forest and a wet meadow. Bottom pebbles, mixed with CPOM, in moderately fast flowing, shallow portions of the creek, were their microhabitat.

Hydraena minutissima (Fig. 3B), originally described from Great Britain (Stephens 1829), is widely distributed in southern, western and central Europe from Spain and Turkey in the south up to the British Isles (Jäch and Skale 2015).

The species was collected in the shallow littoral of the Tara River with pebble deposits on bedrock. The microhabitat was not exposed to strong currents during the time of collection and filamentous algae were partly growing on the surrounding exposed rocks.

Hydraena morio (Fig. 3C) is mainly distributed in eastern and central Europe in an area from Turkey to Germany, including the Balkan Region (Jäch and Skale 2015).

We provide here the first COI 5′-end sequences (Folmer Region) of the species. See also remarks on H. biltoni.

For notes on the habitat, see Hydraena minutissima.

Hydraena nigrita (Fig. 3D), originally described from Germany (Germar 1824), is distributed from Greece and Eastern Europe up to the British Isles (Jäch and Skale 2015).

For notes on the habitat, see Hydraena minutissima.

The samples cluster with Hydraena britteni Joy, 1907, originally described from England and Ireland (Joy 1907), vary only by ca. 0.3% and 2.5%, respectively, in their genetic distance from the latter. Based on the known distribution range of H. britteni, which does not include Montenegro and the genetic distance, it remains uncertain if either specimens are conspecific with the latter. Due to the lack of male specimens, we currently cannot identify these specimens with certainty.

The specimens were collected from fen-like meadows, one (MNE10) densely vegetated with sedge and horsetail, the other (MNE13) additionally with limestone boulders and gravel densely covered with mosses. In both sites, a creek with clear brownish water, rich in humins, was passing the fens and provides continuous water inputs.

The species is distributed in an area between the Adriatic and Black Seas, including the Dinaric Alps (Jäch and Skale 2015).

The taxonomy of this species of the "Haenydra" lineage is not yet finally resolved. Three slightly varying morphs are recognised. Our specimens (Fig. 3E, F) belong morphologically and geographically to “Morph A” sensu Jäch and Díaz (2012). The standard DNA barcode of this morph which we are providing herein varies, in fact, by 0.5% from “Morph B” (Bulgaria).

All specimens were collected from moderately fast flowing, shallow water, but on varying substrates, including submerged wood, grass bunches and pebble.

Habitus as in Fig. 4. Body (labrum to elytral apex) 2.25–2.45 mm long, 0.81–0.86 mm wide. Head, pronotum and elytra dark brown to black, femora and tibiae slightly paler dark brown, palpi and tarsi yellowish-brown. Labrum densely micropunctate, with deep anterior notch; margins slightly upturned. Clypeus medially densely micropunctate, gradually more microstriate laterad. Fronto-clypeal suture bisinuately arched, slightly impressed. Frons medially moderately densely punctate; interstices glabrous; lateral portions densely (sometimes rugosely) bipunctate; micropunctures very dense; interocular grooves indiscernible. Eyes moderately large, distinctly protruding, about 30 facets visible in dorsal view. Maxillary palpi about as long as body width.

Figure 4.  

Digital habitus photographs of Hydraena dinarica, sp. n., paratype ♂; scale bar = 1.0 mm.

Pronotum broadly subhexagonal, moderately wider than long; anterior and posterior margins slightly concave; anterior and posterior angles bluntly rounded, lateral rim denticulate, most conspicuous anteriorly; disc slightly convex; sagittal, anterior and posterior portions densely punctate; remaining disc portions moderately densely punctate; interstices glabrous; anterior and posterior sublateral foveae slightly impressed, rather inconspicuous; entire lateral portions slightly deflexed, rugulously bipunctate, partly microstriate.

Elytra elongate, almost parallel-sided apical 0.15–0.70; disc slightly vaulted, sublaterally more abruptly declivitous; elytral margin moderately explanate up to ca. apical 0.15. Elytra with six regularly arranged, not or slightly impressed rows of puncture striae between suture and disc declivity (approx. at the middle of shoulder) and ca. six additional, less regular puncture striae between disc declivity and elytral margin; punctures moderately large and moderately deeply impressed on anterior disc, gradually slightly decreasing in size and degree of impression towards apex and margin; intervals and interstices flat and glabrous; intervals smaller than puncture diameter anteriorly, larger in posterior and lateral portions; apical sutural teeth present or absent, apices separately rounded, sexually dimorphic (Fig. 5B, C).

Figure 5.  

Hydraena dinarica, sp. n., paratypes: A) ♂ ventral view; B) ♂ elytral apices; C) ♀ elytral apices; D) ♀ ventral abdomen; E) ♀ tergite X; F) gonocoxite; G) ♂ mesotibia; H) ♀ mesotibia; I) ♂ metatibia; J) ♀ metatibia.

Ventral side as in Fig. 5A. Mentum and submentum densely micropunctate. Genae and gula dominantly micropunctate, partly striate; posterior genal ridge distinct, glabrous. Hypomeron micropunctate to microreticulate. Prosternum densely micropunctate with hydrofuge micropubescence, with conspicuous median keel. Mesoventrite densely micropunctate with hydrofuge micropubescence, deeply impressed anterior to mesocoxae; impression transverse-arcuate; with pair of posteriad divergent glabrous streaks lateral to mesocoxae, across mesoventral impression (rather inconspicuous in some specimens); mesoventral disc and process convex. Metaventrite densely micropunctate with hydrofuge micropubescence, central disc shallowly impressed; metaventral plaques distinct, divergent posteriad; intermetacoxal process declined posteriad, predominantly glabrous. Pseudepipleuron longitudinally impressed, with one indistinct puncture stria, rugulose and most anteriorly with hydrofuge pubescence, increasingly glabrous posteriad. Ventrites I–IV (externally visible sternites III–VI) medially flat and with moderately long pubescence (most conspicuous in young specimens), remaining portions with dense, short pubescence; ventrites V and VI largely non-pubescent, glabrous to reticulate.

Male terminal sternite subsemicircular, 0.18 mm wide, not distinguishable from H. saga and similar species (comp. Jäch and Díaz (2017): Figs. 5, 10 and 15); spiculum slightly curved in apical half, 0.70–0.73 mm long (vs. ca. 0.75 mm in H. saga; comp. Jäch and Díaz (2017): Fig. 10).

Aedeagus (Fig. 6): Total length ca. 780 μm; main piece (630 μm long) with three long setae on inner (left) side and a very short one on outer (right) side; apex somewhat variable from convex to obliquely truncate, narrowest subapically; dorsal corner very slightly produced; main piece moderately slender, basal portion rectangularly bent from apical portion, gently narrowed apical 0.25 towards slender, subparallel apical portion; right margin (dorsal view) distinctly roundly produced at about mid-length; prebasal tooth short and blunt. Phallobase subsymmetrical in dorsal and ventral views. Distal lobe generally very similar of that in H. saga and related species, overall more stretched than compact; submembranous contorted distal portion relatively long and wide; opening funnel-like and apicad directed (like in a tuba), located at the most right (behind main piece and distal lobe trunk in dextrolateral view, Fig. 6B); most sclerotised enlarged distal portion with conically-pointed apex in dorsal and ventral views (Fig. 6A).

Figure 6.  

Hydraena dinarica, sp. n. aedeagus (holotype): A) dorsal view: B) lateral view; scale bar = 0.1 mm.

Female tergite X (Fig. 5E), except for suboval shape, very similar to those of H. saga and related species (comp. Jäch and Díaz (2017): Figs. 7 and 12); apex widely rounded; disc with sub-basal squamose setae and with few trichoid setae; squamose setae comparably elongate and not conspicuously widened apically; subapical fringe admedially with dense fringe of vermiform setae of equal length which are slightly bent in apical half and with few long trichoid setae laterally.

Gonocoxite (Fig. 5F) very similar to those of H. saga and related species (comp. Jäch and Díaz (2017): Figs. 6 and 11), subtrapezoidal; hyaline apex round; inner plate moderately projecting basally and laterally; apical area densely pubescent; basal area without setae; cavity oval.

Spermatheca not examined.

Secondary sexual characters: Female elytral apices produced and separately gently rounded, not acuminate. All femora of male slightly more inflated. Male ventrite VI enlarged (Fig. 5A). Male mesotibia with a row of ca. ten denticles along proximal half of mesial face (Fig. 5G), in females only with setae (Fig. 5H). Male metatibia with fringe of long setae at inner face of posterior half (Fig. 5I), in females only with regular setae (Fig. 5J).

Hydraena dinarica, sp. n. is morphologically very similar to species that are referred to as H. saga complex (sensu Jäch and Díaz (2017); see Discussion), namely H. alpicola, H. diazi Trizzino, Jäch & Ribera, 2011, H. emarginata Rey, 1885, H. fosterorum Trizzino, Jäch & Ribera, 2011, H. kahleni Jäch & Díaz, 2017, H. larissae Jäch & Díaz, 2000, H. saga and H. samnitica Fiori, 1904 (original descriptions by Fiori (1904), Jäch and Díaz (2000), Jäch and Díaz (2017), Orchymont (1930a), Rey (1885), Trizzino et al. (2011a)). All of them are most typically characterised by their articulate, contorted aedeagal distal lobe and the rounded or truncate apex of the aedeagal main piece. Hydraena belgica d’Orchymont, 1930; H. dalmatina Ganglbauer, 1901; H. hispanica Ganglbauer, 1901; H. pangaei Jäch, 1992; H. pelops Jäch, 1995 and H. tarvisina (Ferro, 1991) (original descriptions by Ferro (1991), Ganglbauer (1901), Jäch (1992), Jäch (1995), Orchymont (1930b)) were additionally added by Trizzino et al. (2013a)and defined as H. emarginata complex (which would also include H. lotti Bilton, 2013 (see Bilton (2013)). They share the structural plan of the aedeagal distal lobe, but possess an acute aedeagal main piece and lack the minute seta on the outer (right) side of the main piece. Therefore, the latter species are not discussed here in detail, but it should be noted that H. dalmatina might occur sympatrically and is externally quite similar, but can be distinguished by the widely explanate elytral margin in apical third and its elytral apices (acuminate in males, truncate in females).

In comparison with all species mentioned above, Hydraena dinarica, sp. n. is unique in the tuba-like 180° bent hyaline distal tube of the aedeagus (Fig. 6) and thus upward directed opening (vs. downward or lateral directed). Its distal portion is overall larger than in all other species of the H. saga complex (as defined above), except for H. emarginata, some specimens of H. larissae and H. samnitica with subequally large distal portion. Similarly, the aedeagus of H. dinarica, sp. n. is larger (main piece 630 μm long) than most species mentioned above (510–610 μm), except for H. emarginata (610–665 μm).

Within this complex, H. dinarica, sp. n. seems morphologically most similar to the Italian species H. kahleni and H. larissae, especially based on their moderately large contorted aedeagal distal lobe, as well as H. saga on the external habitus. While H. dinarica, sp. n. is slightly larger (2.25–2.45 mm long) than the latter three species (1.95–2.30 mm long), the elytral disc appears slightly flatter and the elytral margin very slightly more explanate in H. dinarica, sp. n. The elytral apices are similar and within the observed variation range in the former species in both sexes. The new species also resembles H. samnitica of almost the same size (especially in the moderately large contorted aedeagal distal lobe), but it is externally distinguishable from H. samnitica by the explanate elytral margin extending almost up to the apex (vs. reaching apical 0.15; the apical area therefore appears more slender in H. dinarica, sp. n.).

On the other hand, H. dinarica, sp. n. seems genetically closest to H. alpicola, H. saga and the H. gracilis Germar, 1824 complex (as defined by Jäch (1995)), based on the DNA barcode (Fig. 7). H. saga occurs in the region (material at NMW; the closest known collection site is in Foča, Bosnia, less than 50 km away from the type locality of H. dinarica, sp. n.) and is also most similar. Therefore, the species can only reliably be identified by dissection of its aedeagus.

Figure 7.  

Statistical parsimony haplotype network of successfully sequenced samples of Hydraena dinarica sp. n., H. biltoni, H. minutissima, H. morio, H. nigrita, H. subintegra, two unidentified female specimens and GenBank records of related species from aligned COI sequences of 567 bp length.

Males can be distinguished as stated above, while in females of H. dinarica, sp. n., the gonocoxite (Fig. 5F) is subtrapezoidal, with evenly round and expanded apical hyaline area (vs. subquadrate gonocoxite and with short apical area in H. saga; Jäch and Díaz (2017): Fig. 11). Furthermore, the female tergite X in H. dinarica, sp. n. (Fig. 5E) is suboval, its basal portion expanded and the vermiform setae of the subapical fringe are bent (vs. subtriangular tergit X with short basal portion and with almost straight subapical vermiform setae in H. saga; Jäch and Díaz (2017): Fig. 12).

Externally, the new species also resembles other representatives of the "Haenydra" lineage which might occur sympatrically, but differ in certain characters: Hydraena bosnica Apfelbeck, 1909 (posteriorly sinuate pronotum, oval elytra; Trizzino et al. (2013a): Fig. 42a); H. excisa Kiesenwetter, 1849 (clypeus shagrened; elytra less elongate, more oval with disc more convex, margin more explanate, apices slightly truncate in males, sharply (not roundly) notched in females; Trizzino et al. (2013a): Fig. 32l); H. gracilis balcanica d'Orchymont, 1930 (elytra with disc more convex, margin less explanate, apices almost conjointly rounded in males; Trizzino et al. (2013a): Fig. 24a); H. phallica d'Orchymont , 1930 (clypeus shagrened; elytra more oval with disc more convex, apices slightly truncate in males, shallowly notched in females; Trizzino et al. (2013a): Fig. 32p); H. subintegra (smaller and paler, elytra reddish-brown with disc more convex, margin more explanate, apices conjointly rounded in both sexes); H. vedrasi d’Orchymont, 1931 (elytra with disc more convex, apex subtruncate in males, sharply (not roundly) notched in females; Trizzino et al. (2013a): Figs. 22a and g) (original descriptions by Apfelbeck (1909), Kiesenwetter (1849), Orchymont (1930a), Orchymont (1930b), Orchymont (1931)).

Hydraena dinarica, sp. n. varies by 0.6% genetic distance (657 bp CO1 barcode from the most similar congeners H. alpicola and H. saga and by 3.3% from the morphologically similar H. larissae (Suppl. material 1).

This species was collected from a mountain stream in a forested, undisturbed karst area at an altitude of about 1220 m a.s.l. (Fig. 2). During the time of collection, the river was only partly on the surface; the predominant flow was subsurface, causing low water temperatures. The well-shaded riverbed, including the water-bearing reaches, was densely covered with mosses. The specimens were collected from the upper interstitial of the bottom gravel (mesopsammon) in shallow, partly rapidly flowing water.

So far only known from the type locality at the northern slopes of Durmitor Mt., Montenegro (Fig. 8).

Figure 8.  

Map of Europe with the collection site of Hydraena dinarica sp. n. and the distribution of morphologically similar species of the "Haenydra" lineage defined as "Hydraena emarginata complex" by Trizzino et al. (2013a) and H. gracilis as genetically similar species with overlapping range.

The species is named after the Dinaric Alps, or Dinarides, a karst mountain range where Durmitor Mt. and the type locality of the new species are situated. The epithet is used as an adjective meaning "of the Dinaric Alps".