Stygobromus anastasiae Sidorov, Holsinger & Takhteev, 2010, n. sp.

Stygobromus anastasiae n. sp.

Figures 36 – 67, 69, 72 – 75

Stygobromus sp. – Takhteev & Ambrosova 2001: 125. – Galimzjanova et al. 2008: 128. – Sidorov et al. 2008: 88.

Material examined. Holotype: female, 3.8 mm. 1/88455-ZINRAS, Russia, Irkutsk City, University Spring (52°15΄0 43ʺ N; 104°14΄402ʺ E), 24 Feb 2003, collected by E.V. Ambrosova. Paratypes: 14/23sd-IBSS, 2 males (2.5 mm), same locality as holotype, 27 Jul 2003, collected by E.V. Ambrosova; female (2.5 mm), male (2.5 mm), Irkutsk area (Shelekhov territory), Olkhinsky Spring (5°209΄505ʺ N; 104°0 6΄267ʺ E), 26 Jul 2007, collected by V.V. Takhteev, 0 6 Jul 2006, collected by A.V. Galimzjanova; JRH-4550, 1 specimen (2.5 mm), same locality as holotype, 1 Jun 2003, collected by E.V. Ambrosova; JRH-4551, 1 specimen (2.5 mm), Russia, Irkutsk area (Shelekhov territory), Olkhinsky Spring, 24 Sept. 2006, collected by A.V. Galimzjanova.

Material for SEM. Female (3.0 mm), male (2.8 mm), (whole body on 1 stage and 1 stage with appendages), same locality as holotype, 21 Feb 2001, 27 Jul 2003, collected by E.V. Ambrosova.

Diagnosis. Eyeless, unpigmented, subterranean species (Fig. 36) of stygomorphic facies. Inner plate of maxilliped narrowing apically, with 2 simple spines, 1 plumose spine and 2 naked setae. Coxal plates 3–4 shallow. Bases of pereopods 5–7 narrow, distoposterior lobes poorly defined. One pair simple lateral sternal gills on pereonite 7. Largest female 3.8 mm, largest male 3.0 mm.

Further distinguished from the two Altaic species described above by the following character differences: flagellum of antenna 2 with 3 segments; palp segments 1–2 of maxilla 1 in length ratio 0.25:1; tip of palp segment 2 of maxilla 1 extending beyond spines of outer plate; inner plate of maxilla 1 with 3 plumose setae; mandibular processes of lower lip proportionately longer and narrower; inner plate of maxilliped with 2 simple spines, 1 plumose spine and 2 naked setae apically; reduction of setae on posterior margin of gnathopod propodi; coxal plates 3–4 shallow/reduced in size; bases of pereopods 5–7 narrow and lacking distinct distoposterior lobes; pleopod 3 with reduced number of segments in both rami; uropod 3 with 2 spines; telson tapering distally, not subquadrate, armed with 5–6 shorter spines.

Description. Female (3.8 mm). Antenna 1 (Fig. 37): 30 % length of body, about 50 % longer than antenna 2; peduncular segments 1–3 in length ratio 1:0.7:0.4; primary flagellum with 9 segments; 5 flagellar segments bearing lanceolate aesthetascs accompanied by setae. Antenna 2 (Figs 36, 38): peduncular segments 4 and 5 of equal length; flagellum with 3 segments. Upper lip (Fig. 42) subrounded, with minute setae at apex. Mandibles subequal: left mandible (Fig. 45) with 5-dentate incisor and lacinia mobilis, spine row with 3 serrated spines, triturative molar with seta; right mandible (Fig. 46) with 5-dentate incisor, lacinia mobilis trifurcate; segment 2 of palp broad with 2 long setae, segment 3 as long as segment 2 but narrower, bearing 2 A-setae, 6 D-setae and 4 E-setae. Lower lip (Fig. 44) with inner lobes. Maxilla 1 (Fig. 39): inner plate with 3 plumose setae, outer plate with 7 serrated spines; palp segment 2 approximately 4X longer than segment 1, bearing 3 slender spines and 2 stiff setae on apex. Maxilla 2 (Fig. 40): inner plate stout, with oblique row of 3 plumose setae on inner margin near apex, outer plate narrower and bearing 5 slender setae on apex. Maxilliped (Fig. 41): inner plate apically with 2 simple spines, 1 plumose spine and 2 naked setae; outer plate with row of naked setae on inner margin and apex; palp segment 2 with row of bifid setae on inner margin. Lateralia (Fig. 43) subquadrate, with 9–10 strong barbed spines.

Gnathopod 1 (Fig. 47): coxal plate shallow, broader than deep, with 2 short setae on ventral margin; basis broadest distally, with 2 long plumose setae on posterior margin and 2 long and 1 short setae on inner face; propodus of gnathopod 1 little larger than propodus of gnathopod 2; propodus subovate, palm nearly straight and armed with 6 or 7 distally-notched spines near defining angle; posterior margin much shorter than palm, with 1 short seta; dactylus with 1 spine and 2 fine seta on inner margin. Gnathopod 2 (Fig. 48): coxal plate broader than deep, with 2 short setae on ventral margin; basis “bottleshaped”, with few long, plumose setae on anterior and posterior margins; propodus subovate, palm slightly concave, armed with 6 distally notched spines accompanied by 2 sets of setae in defining angle area; dactylus with 1 spine and 3 fine seta on inner margin near nail.

Pereopods 3 and 4 (Figs 49, 50) subequal; coxae subrectangular, broader than deep, ventral margins with 2 short setae each; dactyli exceeding 50 % length of corresponding propodi. Pereopods 5–7 (Figs 51–53): subsimilar, bases narrow and lacking distinct disto-posterior lobes; pereopod 6 longer than 5 and 7; dactyli 35–40 % length of corresponding propodi, bearing 1 stiff setae on inner margin in base of nail.

Coxal gills on gnathopod 2 and pereopods 3–6 stalked and subovate. One pair simple lateral sternal gills on pereonite 7 (Fig. 55). Oostegites on pereopods 2–5 (Fig. 48) sublinear with short, sparse marginal setae.

Pleonal plates 1–3 (Figs 36, 54): posterior margins straight (but weakly convex in plate 3), with 1 seta each; posterior corners indistinct, broadly rounded; ventral margins of plates without setae. Pleopods 1–3 (Figs 56–58): peduncular segments with 2 coupling spines (retinaculae) each; both rami of each pleopod fringed with plumose setae; pleopod 3 with comparatively fewer number of segments in both rami. Urosomites (Fig. 36) free, commissures pronounced, bearing sparse setae on dorsal face. Uropod 1(Fig. 59): outer ramus subequal in length to inner ramus, approximately 85 % length of peduncle, armed with 7 spines; inner ramus with 5 spines, peduncle with 4 spines. Uropod 2 (Fig. 60): outer ramus subequal in length to inner ramus, approximately equal in length to peduncle, armed with 5 spines; inner ramus with 6 spines, peduncle with 2 spines. Uropod 3 (Fig. 61): ramus about 50 % length of peduncle but only about 50 % as wide, armed apically with 2 spines. Telson (Fig. 62) slightly longer than broad but tapering distally, apical margin with vestigial notch and 5–6 weakly notched spines.

Male (2.5 mm). Closely similar to female but apparently reaching sexually maturity at smaller size and differing in few characters as follows. Mandibular palp (Fig. 66): segment 2 broad, with 1 long setae; segment 3 as long as segment 2, bearing 1 A-seta, 3 D-setae, and 4 E-setae.

Gnathopod 1 (Figs 64, 72–74): propodus of gnathopod 1 smaller than that of gnathopod 2; propodus subtriangular, palm straight, armed with 4 distally notched spines accompanied by setae near defining angle; dactylus with 1 small spine and 3 fine seta on inner margin. Gnathopod 2 (Fig. 65): propodus subtriangular, palm straight, armed with 4 distally notched spines accompanied by setae at defining angle; dactylus with 1 tiny spine and 3 fine seta on inner margin. Uropod 1 without peduncular process. Uropod 2 (Fig. 67): inner ramus little longer than outer ramus and peduncle, armed with 6 spines; peduncle armed with 2 spines; outer ramus without spines on medial side. Telson (Fig. 63) longer than broad and tapering distally; apical margin straight and armed with 4–5 spines.

Variation. Setation of the mandible palp varies according to age (and body size) of specimens.

Type locality. Russia, Irkutsk City, the University spring (52°15΄0 43ʺ N; 104°14΄402ʺ E).

Etymology. Named in honor of hydrobiologist Anastasia Galimzjanova (Department of Biological and Soil Sciences, Irkutsk State University, Russia).

Distribution and ecology. Stygobromus anastasiae n. sp. is an inhabitant of subterranean groundwater in South Pribaikalye. The species was sampled from two low-mineralized and non-freezing springs in the drainage basin of the Angara River (Fig. 1). The first, University spring, consists of small groundwater outlets with depths of 3–17 cm and a mixed substrate composition of anisomerous sand grains, stones and pebbles. In addition, the hydrochemical composition of the groundwater was hydrocarbonate magnesium-calcium. The temperature range was 4.4–5.0° С, and mineralization was 0.34 g /l, pH 6.25.

The Olkhinsky spring has a depth of 19–30 cm, with a substrate consisting of a mixture of anisomerous sand grains, breakstones and gravels. The hydrochemical composition of the water is chloride-hydrocarbonate sodium-magnesium, with a temperature of 4.5–5.0° C and mineralization 0.3 – 1.6 g /l, pH 7.25–7.7.

The meiofauna of Olkhinsky spring was composed of the ostracod Ilyodromus estonicus Jarvekulg, and the harpacticoids Attheyella nordenskjoldi (Lilljeborg) and Bryocamptus zschokkei caucasicus Borutzky (Galimzjanova et al. 2008). The female amphipods had well developed brood plates but eggs or newly developed juveniles were not present in the brood pouch.