Luchoelmis kapenkemkensis sp. nov.

Type material. Holotype (male): Argentina, Chubut Province, Arroyo Nant y Fall int. Rt. prov. 17; iv.2008; C. Brand Coll.

Paratypes: Argentina, Chubut Province, Arroyo Nant y Fall int. Rt. prov. 17: 3 ex 8.iii.2008 M. Archangelsky coll.; 2 ex iii.2008 C. Brand coll.; 10 ex iv. 2008 C. Brand coll.; 1 ex ii.2009 C. Brand coll.; 2 ex 2.ii.2011 M. Archangelsky coll.

Diagnosis. The new species can be easily recognized from other known species of the genus by the following combination of characters: 1) color pattern with two reddish-brown areas on each elytron (Fig. 1); 2) presence of plastron on margins of abdominal ventrites I–III (Figs 2, 3); 3) presence of cleaning fringes on distal half of meso- and metatibiae; 4) shape of the male genitalia (Figs 6, 7).

Description. Holotype: male, 2.1 mm long; 0.8 mm wide. Length range: 1.9–2.1 mm.

Color: shiny, very dark brown except for antennae, femora and tibiae (except apex of femora and base of tibiae) and pretarsal claws reddish brown; each elytron with two reddish-brown markings (Fig. 1), basal one smaller, close to inner margin, distal one larger, elongate, subapical on distal half close to outer margin.

Plastron on pronotal hypomeron and inner margin of epipleuron, sides of pro- meso- and metasternum, outer face of pro- and mesocoxa, surrounding basal half of profemur and mesofemur, and sides of ventrites I–III (Figs 2, 3).

Head bent downwards, opisthognathous, covered by fine punctuation, punctures separated by 2–3 times their diameter. Fronto-clypeal suture evident, between antennal sockets. Labrum large, rectangular, wider than long. Antennae filiform, shorter than pronotum, distal antennomere the longest.

Thorax. Pronotum widest behind middle, wider at base than at anterior margin; anterior margin convex, covering base of head capsule (Fig. 1); lateral margins sinuate; posterior margin trisinuate. Disc of pronotum with large median gibbosity in posterior half; one strong central depression anterior to gibbosity, two smaller depressions on antero-lateral corners, two elongate small depressions behind central gibbosity joining together and forming V-shaped groove, two small central foveae at base, close to scutellar emargination. Surface covered by fine punctures, separated by 1–2 times their diameter. Prosternum in front of coxae short, prosternal process narrow, elongated and parallel-sided, with rounded apex, reaching base of mesosternum. Mesosternum with groove for reception of prosternal process, concave between mesocoxae. Metasternum large, convex on anterior half, with elongate triangular depression along midline on posterior half. Pro- and mesocoxa rounded, metacoxa transverse, subtriangular; outer margins of pro- and mesocoxa with plastron; femora as long as tibiae, pro- and mesofemur with plastron on basal half; tibiae slender, those of meso- and metathoracic legs with cleaning fringe on distal half (also present in females); tarsi longer than tibiae, apical tarsomere as long as preceding four tarsomeres combined; pretarsal claws simple, lacking basal tooth.

Abdomen with five visible ventrites (Fig. 2), convex laterally, without lobes; ventrites I–III with plastron on sides, disc of ventrites glabrous, with fine microsculpture; ventrites IV and V glabrous, microsculptured; distal margin of ventrite V evenly convex, margined with short golden setae.

Male genitalia: median lobe longer than parameres (Figs 6, 7), broader in middle portion, becoming slender in distal half, and constricted before rounded apex; phallotreme wide, almost at midlength of penis. Parameres broad at base, narrowing towards apex. Phallobase shorter than parameres and median lobe, longer than wide, asymmetrical, with three basal projections.

Habitat and biology. Nant y Fall stream is a 3rd order stream tributary of the Futaleufú river, and is located in a transitional mountain and piedmont area in the Northwest of Chubut province, Argentina. It belongs to the ecotone between the Subantarctic forest and the Patagonian steppe phytogeographical provinces. The substrate at the studied site is composed of gravel, cobbles, and boulders, with sand and smaller fractions at pools and depositional areas. Aquatic vegetation is abundant and diverse, with Isoetes savatieri being the dominant species in riffles and Myriophyllum quitense and Callitriche lechleri in pools. Current speed ranged from 0.22 to 1.16 ms -1, water temperature ranged from 4 to 18 °C, with an annual average of 11.6 °C; during the entire year water remains well oxygenated (9.95–13.88 mgl -1 O2) and above saturation (114.1–121.4 %) (Brand & Miserendino 2012, Brand et al. 2012). Larvae assigned to L. kapenkemkensis were found at all habitats, both erosional and depositional, while adults appeared to be most abundant in erosional boulder-pebble substrates.

Etymology. From kapen (Tehuelche, Boreal-Meridional= red) and kemken (Tehuelche, Boreal-Meridional= back), for the reddish-brown spots on the elytra. The Tehuelche people, also known as “Patagones”, inhabited southern Argentina and Chile. Both Tehuelche words were taken from the Tehuelche dictionary (Casamiquela 2008).

Key to the species of Luchoelmis (adapted from Spangler & Staines 2002)

1. Pronotum with basal margin as wide as anterior margin; male genitalia as in Fig. 9 .......... L. aequalis Spangler & Staines

- Pronotum with basal margin wider than anterior margin; male genitalia not as in Fig. 9.............................. 2

2. Each elytron with two reddish markings as in Fig. 1. Abdominal ventrites I–III with plastron on sides (Figs 2, 3). Meso- and metatibiae with cleaning fringes on distal half. Male with median lobe of aedeagus strongly narrowing on distal half (Figs 6, 7). Small species, 1.9–2.1 mm .................................................. L. kapenkemkensis new species

- Elytra reddish-brown to black, without markings (Fig. 4). Abdominal ventrites I–III without plastron on margins (Fig. 5). Tib- iae with or without cleaning fringes. Median lobe of aedeagus different. Larger species, 2.1–2.4 mm ................... 3

3. No femora with cleaning fringe. Pronotum widest at about midlength; male genitalia as in Fig. 10 ..................................................................................................... L. penai Spangler & Staines

- Pro- and mesofemora with cleaning fringe on some surfaces. Pronotum widest behind midlength; male genitalia not as in Fig. 10................................................................................................. 4

4. Female without cleaning fringe on front surface of profemora. Male genitalia as in Fig. 8 .. L. cekalovici Spangler & Staines

- Female with cleaning fringe on front surface of profemora. Male genitalia as in Fig. 11 .. L. magallanensis Spangler & Staines