Stygobromus anastasiae, Sidorov, Dmitry A., Holsinger, John R. & Takhteev, Vadim V., 2010

Sidorov, Dmitry A., Holsinger, John R. & Takhteev, Vadim V., 2010, Two new species of the subterranean amphipod genus Stygobromus (Amphipoda: Crangonyctidae) from Siberia, with new data on Stygobromus pusillus (Martynov) and remarks on morphology and biogeographic relationships, Zootaxa 2478, pp. 41-58 : 50-55

publication ID	https://doi.org/ 10.5281/zenodo.195357
DOI	https://doi.org/10.5281/zenodo.6208713
persistent identifier	https://treatment.plazi.org/id/03C98791-FFAA-FFDC-D080-B579FCF2CA27
treatment provided by	Plazi
scientific name	Stygobromus anastasiae
status	sp. nov.

Treatment

Stygobromus anastasiae View in CoL n. sp.

Figures 36 – 67 View FIGURE 36 View FIGURES 37 – 48 View FIGURES 49 – 67 , 69, 72 – 75 View FIGURES 68 – 75

Stygobromus View in CoL 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 View FIGURE 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 View FIGURES 37 – 48 ): 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 View FIGURE 36 , 38 View FIGURES 37 – 48 ): peduncular segments 4 and 5 of equal length; flagellum with 3 segments. Upper lip ( Fig. 42 View FIGURES 37 – 48 ) subrounded, with minute setae at apex. Mandibles subequal: left mandible ( Fig. 45 View FIGURES 37 – 48 ) with 5-dentate incisor and lacinia mobilis, spine row with 3 serrated spines, triturative molar with seta; right mandible ( Fig. 46 View FIGURES 37 – 48 ) 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 View FIGURES 37 – 48 ) with inner lobes. Maxilla 1 ( Fig. 39 View FIGURES 37 – 48 ): 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 View FIGURES 37 – 48 ): 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 View FIGURES 37 – 48 ): 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 View FIGURES 37 – 48 ) subquadrate, with 9–10 strong barbed spines.

Gnathopod 1 ( Fig. 47 View FIGURES 37 – 48 ): 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 View FIGURES 37 – 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 View FIGURES 49 – 67 ) 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 View FIGURES 49 – 67 ): 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 View FIGURES 49 – 67 ). Oostegites on pereopods 2–5 ( Fig. 48 View FIGURES 37 – 48 ) sublinear with short, sparse marginal setae.

Pleonal plates 1–3 ( Figs 36 View FIGURE 36 , 54 View FIGURES 49 – 67 ): 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 View FIGURES 49 – 67 ): 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 View FIGURE 36 ) free, commissures pronounced, bearing sparse setae on dorsal face. Uropod 1( Fig. 59 View FIGURES 49 – 67 ): 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 View FIGURES 49 – 67 ): 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 View FIGURES 49 – 67 ): ramus about 50 % length of peduncle but only about 50 % as wide, armed apically with 2 spines. Telson ( Fig. 62 View FIGURES 49 – 67 ) 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 View FIGURES 49 – 67 ): 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 View FIGURES 49 – 67 , 72–74 View FIGURES 68 – 75 ): 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 View FIGURES 49 – 67 ): 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 View FIGURES 49 – 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 View FIGURES 49 – 67 ) 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 View FIGURE 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.