Stygobromus mikhaili, 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 : 46-50

Stygobromus mikhaili n. sp.

Figures 8 – 35 , 68, 70, 71

Material examined. Holotype: female, 2.8 mm, 14/21sd-IBSS, Russia, Altay Rep., small spring on the right bank of the Chuya River, 500 m below the Kyzyltash River mouth (50°13΄571ʺ N; 87°40΄322ʺ E), 23 Aug. 2005, collected by M.V. Chertoprud. Paratypes: 2 female paratypes (3.5 mm, 3.3 mm) and 1 male (2.6 mm), 14/22sd-IBSS, same data as holotype.

Material for SEM. Male, 2.6 mm, (1 stage with appendages), same data as holotype.

Diagnosis. Small, eyeless, unpigmented, subterranean species ( Fig. 8 ) of stygomorphic facies, distinguished by stout maxilliped palp armed with bifid setae; propodus of female gnathopod 1 approximately equal in size to that of gnathopod 2 but differing slightly; propodi of male gnathopods proportionately larger; propodus of male gnathopod 1 armed with 6 spines at defining angle, that of gnathopod 2 with 4 such spines. Paired median sternal gills on pereonites 2–4, and 1 pair of simple lateral sternal gills on pereonite 7. Largest female 3.5 mm, largest male 2.6 mm.

Further differentiated from S. pusillus (see above), geographically the nearest other known species in the genus, as follows: all spines on outer plate of maxilla 1 equal in length; row of plumose setae on inner plate of maxilla 2 narrowing apically and with 4 plumose seta (as opposed to inner plate of maxilla 2 of S. pusillus , which is rounded but not tapered and bears fewer plumose setae); inner lobes of lower lip pronounced as opposed to vestigial lobes in S. pusillus ; propodus of female gnathopod 1 little larger than propodus of gnathopod 2 (that of S. pusillus is a little smaller); propodi of female gnathopods bearing few more spines at defining angle of palms than propodi of S. pusillus ; dactyl of pereopod 7 shorter than that of S. pusillus ; and telson bearing few more apical spines. In addition, the body surface of S. mikhaili n. sp. is more densely covered by sensillae.

Description. Female (2.8 mm). Antenna 1 ( Fig. 9 ) 30 % length of body, about 50 % longer than antenna 2; peduncular segment 1 bearing 2 plumose seta; primary flagellum with 10 segments, all but terminal segment bearing lanceolate aesthetascs accompanied by setae. Antenna 2 ( Fig. 10 ): flagellum with 4 segments. Mandibles subequal: left ( Fig. 12 ) with or 5-dentate incisor and lacinia mobilis, spine row with 2–4 serrated spines, molar triturative, with plumose seta; right mandible ( Fig. 13 ) with 5-dentate incisor and trifurcate lacinia mobilis and spine row with 2 serrated spines; molar triturative with plumose seta; segment 2 of palp broad with 2 long setae accompanied by row of setules, segment 3 shorter than segment 2 and bearing 1 A-seta, 3 D-setae and 3 E-setae. Lower lip ( Fig. 14 ) with small inner lobes. Maxilla 1 ( Fig. 11 ): inner plate small and tapered apically, with 2 plumose setae; outer plate with 7 serrated spines; palp segment 2 about 30 % longer than segment 1 and bearing 4–5 stiff setae on apex. Maxilla 2 ( Fig. 17 ): inner plate broader than outer plate, with oblique row of 4 plumose setae on inner margin toward apex; outer plate with 8 slender setae apically. Lateralia ( Fig. 16 ) subquadrate, with 6 weakly barbed spines and 4 simple stiff setae. Maxilliped ( Fig. 15 ): inner plate with 4 serrated spines and 2 naked setae apically; outer plate with row of naked setae on inner margin and apex; palp segment 2 broad and twice length of segment 1, inner margin armed with row of stiff setae, some bifid; nail of dactyl (palp segment 4) sharply pointed.

Gnathopod 1 ( Fig. 18 ): coxal plate subrectangular, bearing 2 long setae on ventral margin; basis stout, with 3 long setae on posterior margin and with 2 long and 2 short setae on inner face; propodus subequal in size to that of gnathopod 2; palm straight and equal in length to posterior margin, armed with 1 long distally notched spine tooth and 5 shorter distally notched spine teeth on defining angle; posterior margin straight with two bifid setae; dactyl with 1 median seta on the inner face and 2 seta near base of nail. Gnathopod 2 ( Fig. 19 ): coxal plate deeper than broad, bearing 2 setae on ventral margin; basis slightly curved, with 3 long setae on posterior margin and 1 long seta on inner face; palm of propodus slightly convex and equal in length to posterior margin, armed with 1 long, distally notched spine tooth and 3 short distally notched spine teeth on defining angle; posterior margin straight and bearing two sets of 2 long setae, ventral setae and several shorter ones; dactyl with 1 median seta on the inner face and 2 seta near base of nail.

Pereopods 3 and 4 ( Figs 22, 23 ) longer than pereopod 5 but shorter than pereopod 6 and subsimilar except for few details as noted; coxa of pereopod 3 pear-shaped, with 2 setae on ventral margin, basis bearing 3 long marginal setae; coxa of pereopod 4 broader, posterior margin slightly concave, ventral margin slightly convex, with 3 short setae; basis with 1 long seta; dactyli about 50 % length of corresponding propodi. Pereopods 5–7 ( Figs 24–26 ): 6 longer than 5 and 7, bases with convex posterior margins and short marginal setae, distoposterior lobes well defined; dactyli of pereopods 6 and 7 50–55 % length of corresponding propodi, that of pereopod 5 abut 65 % length of corresponding propodus. Coxal gills on pereopods 2–6 stalked and subovate. Paired median sternal gills on pereonites 2–4, 1 pair lateral sternal gills on pereonite 7 ( Fig. 27 ). Oostegites on pereopods 2–5 sublinear with long marginal setae.

Pleonal plates 1–3 ( Fig. 28 ): posterior margins nearly straight, with 1 seta each well above broadly rounded corners; ventral margin of plate 3 with 1 spine. Pleopods 1–3 ( Figs 33–35 ): peduncular segments with 2 coupling spines (retinaculae) each; rami fringed with plumose setae; pleopod 3 shorter than pleopods 1 and 2, with reduced number of segments in outer ramus. Urosomites free, with pronounced commissures, bearing sparse setae on dorsal face. Uropod 1( Fig. 29 ): inner ramus subequal in length to outer ramus, rami about 75 % length of peduncle; peduncle with 5 spines; inner ramus with 5 spines, outer ramus with 6 or 7 spines. Uropod 2 ( Fig. 30 ): inner and outer rami subequal in length and a little shorter than peduncle; peduncle armed with 3 spines. Uropod 3 ( Fig. 31 ): ramus about 50 % length of peduncle, armed with 4 prominent apical spines. Telson ( Fig. 32 ) subquadrate, apical margin slightly convex and armed with 10 prominent spines, some as long as the telson itself.

Male (2.6 mm). Gnathopod 1 ( Fig. 20 ): propodus little shorter than that of gnathopod 2; palmar margin slightly concave and little longer than posterior margin, armed with 1 long distally notched spine tooth and 2 short distally notched spine teeth on defining angle; posterior margin convex and with two setae; dactyl with 1 median seta each on inner and outer margins. Gnathopod 2 ( Fig. 21 ): palmar margin slightly convex and subequal in length to posterior margin, armed with 1 long distally notched spine tooth, 2 short distally notched spine teeth and 2 long setae at defining angle; posterior margin straight with two sets of 2 setae each; dactyl similar to that of gnathopod 1. Uropod 1 lacking a peduncular process.

Type locality. A small nameless spring (50°13΄571ʺ N; 87°40΄322ʺ E) on right bank of the Chuya River, 500 m below mouth of the Kyzyltash River, in the Altay Republic of Russia (see Fig. 1 ).

Etymology. It is a pleasure to name this new species in honor of our colleague hydrobiologist Mikhail Chertoprud in the Department of Biological Sciences, Moscow State University, Russia.

Distribution and ecology. Stygobromus mikhaili n. sp. is known to date only from an outlet of subterranean groundwater on the right bank of the Chuya River in the Altay Mountains ( Fig. 1 ) of southcentral Russia. The small, nameless spring is apparently a hypotelminorheic habitat (see Culver & Pipan 2009; Holsinger 2009) consisting of small groundwater outlets at a depth of 5–7 cm in a substrate consisting of stones overgrown with moss. Mature females with well developed brood plates but without eggs or larvae were collected.

Figures

FIGURE 1. Distribution of Stygobromus in Central Asia: (1) S. pusillus (Martynov) in the Biya River and Teletskoye Lake; (2) S. mikhaili n. sp. in the Chuya River basin; (3) S. anastasiae n. sp. in the Angara River basin; (4) S. kazakhstanica Kulkina in the Chernaya River basin.

FIGURE 8. Stygobromus mikhaili n. sp., male (2.6 mm) from left side (dorsal surface crumpled), SEM.

FIGURES 9 – 21. Stygobromus mikhaili n. sp., female, holotype: (9) antenna 1; (10) antenna 2; (11) maxilla 1; (12, 13) left and right mandible; (14) lower lip; (15) maxilliped; (16) lateralia; (17) maxilla 2; (18) gnathopod 1; (19) gnathopod 2. Male paratype (2.6 mm): (20) gnathopod 1; (21) gnathopod 2. Scale bars 0.1 mm.

FIGURES 22 – 35. Stygobromus mikhaili n. sp., female, holotype: (22) pereopod 3; (23) pereopod 4; (24) pereopod 5; (25) pereopod 6; (26) pereopod 7; (27) pereonite 7 coxal gill; (28) pleonal plates; (29) uropod 1; (30) uropod 2; (31) uropod 3; (32) telson. Female paratype (3.3 mm): (33, 34, 35) pleopods 1 – 3. Scale bars 0.1 mm.

FIGURES 68 – 75. (68, 70, 71): Stygobromus mikhaili n. sp., male (2.6 mm): (68) tip of antenna 2; (70) propodus of gnathopod 2; (71) squamiferous membrane along inner margin, idem. (69, 72 – 75): Stygobromus anastasiae n. sp., female (3.0 mm), male (2.8 mm): (69) tip of antenna 2, female; (72) propodus of gnathopod 1, male; (73) squamiferous membrane along inner margin, idem; (74) squamiferous membrane in base of nail, idem; (75) squamiferous membrane in base of nail, female. SEM.