Cytherissa obrutshevi Mazepova, 1990

Alekseeva, Tatyana M., Krivorotkin, Roman S. & Timoshkin, Oleg A., 2025, Redescriptions of ten endemic Cytherissa species (Ostracoda, Podocopida, Cytherideidae) from the coastal and deep-water zones of Lake Baikal, Zootaxa 5673 (3), pp. 301-354 : 326-327

Cytherissa obrutshevi Mazepova, 1990

Figs. 19–21 ; 22B, 22E ; 38G ; 39F ; 40B, 40H .

Type locality. Lake Baikal , one of two locations: 1) shallow water near Bolshoy Ushkaniy Island (approximate coordinates 53º51’06.48” N, 108º40’01.35” E); 2) shallow water near Kocherikovsky Cape (approximate coordinates 53º44’41.85” N, 107º52’27.82” E) .

Type material. Lectotype No. O13 (female) and paralectotype No. 1 (male): dwm No. O5-180872. Paralectotypes Nos. 2–14 (13 females): dwm No. O6-180872. Paralectotype No. 15 (male): dwm No. O7-180872. Paralectotype No. 16 (male): dwm No. O7-180872 (valves) and wm No. O8-180872 (limbs). Paralectotype No. 17 (male): dwm No. O7-180872 (valves) and wm No. O9-180872 (limbs). Paralectotypes Nos. 18–26 (4 females; 5 males): swm No. 18. Paralectotype No. 27 (female): swm No. 18 (valves) and wm No. O10-180872 (limbs).

All ostracods were collected from two locations: 1) shallow water of Bolshoy Ushkaniy Island, August 18, 1972, depth 20 m, sand and stones with sponges, sample No. 395 from the collection of taxocoenoses of G.F. Mazepova; 2) near Kocherikovsky Cape, August 8, 1973, depth 5 m, sample No. 482 from the collection of taxocoenoses of G.F. Mazepova. Since all specimens were in one tube with a common label, we did not determine where each specimen was collected from.

Description. Female. Carapace ( Figs. 19A–19D ; 20A–20F ; 39F ) laterally irregularly trapezoidal: L=990–1040 µm (mean 1030 µm, n=10), largest H=650–675 µm (mean 665 µm, n=10), situated slightly behind posterior border of anterior 1/ 4 L. Dorsal margins of valves slightly arched at center. Anterior end of carapace broadly rounded, posterior end narrowly rounded, almost straight. Ventral margins of both valves equally concave on inner side; ventral margin of RV concave on outer side as on inner side, and straight on LV. LV overlaps RV throughout except for dorsal margin. Both valves in center of ventral margin with weakly visible protrusions (resembling similar ones in Cytherissa burchani Mazepova, 1990 ); very small posterior-ventral protrusion on RV. Margins of protrusions smoothly passing to margin of valves. Inner lamella broad. Marginal pore canals long, occupying 80–100% of width of inner lamella and ending in sensilla. Inner lamella of each valve with 34–35 marginal pore canals. Pore canals of outer lamella sieve-type, branching, grouped (up to five canals in group), single near margin of valves; each canal with one sensillum. Outer lamella of each valve with at least 95–115 pore canals. Inner side of each valve with about 40–45 canal apertures. Hinge teeth on RV, crenulated, not extending beyond valve margin; bar on LV, slightly crenulated. Microrelief of valves surface homogeneous, consisting of small circular pits; diameter and depth of pits slightly decreasing at margins of valves ( Fig. 22B ). Site of greatest width of carapace on ventral and dorsal views weakly pronounced and located at site of central 1/3 L ( Fig. 20C, 20D ).

A1, A2, Md, Mxl, L5–L7 as in C. heckyi , but distal segments of L5–L7 partially fused.

Male. Carapace ( Figs. 19E–19H ; 21A–21F ; 39F ) slightly longer and lower than in female: L=1065–1120 µm (mean 1090 µm, n=6), H=650–675 µm (mean 660 µm, n=6). In dorsal and ventral views, males ( Fig. 21C, 21D ) narrower than females ( Fig. 20C, 20D ). Site of greatest width less pronounced. Posteroventral protrusion of RV larger than in female; ventral-medial protrusions very weakly pronounced and shifted closer to center of valves. Geniculate (transformed) legs on right side of body. Other morphological features of carapace structure, microrelief, A1, A2, Md, Mxl, left (non-geniculate) legs L5 and L6 as in female. Both legs of L7 and right (geniculate) L5 as in male C. heckyi , but distal segments of non-geniculate L5 ( Fig. 40B ), L6 and both L7 partially fused.

L6. Right leg. Protopod with four setae and several groups of pseudochaetae. Endopod one-segmented ( Fig. 40H ), with one seta in center of segment and distal gently pointed outgrowth.

Hemipenis ( Figs 22E ; 38G ) large, elongate-triangular; outer appendage triangular, with spatulate widened tip. Length of hemipenis in quiescent state 515 µm (n=1), greatest width 340 µm. Diameter of copulatory process 180–215 µm.

Brush organ. Both rami with 12 apical setae, row of small pseudochaetae in medial part and row of pseudochaetae in subapical part; row of apical pseudochaetae either very small or absent.

Differential diagnosis. The shells of C. obrutshevi individuals are morphologically similar to the specimens of Cytherissa florensovi Mazepova, 1990 and C. golyschkinae . The species differ by the valve outlines laterally and carapace shape in dorsal and ventral views. G.F. Mazepova (1990: pp. 312) mentioned that C. obrutshevi and C. florensovi were considered in common for a long time.

Notes. The list of type specimens ( Mazepova 2001: pp. 542) includes 30 paratypes (20 females and 10 males). The handwritten version of G.F. Mazepova lists 39 type specimens (26 females and 13 males). The tube label shows 30 type specimens (20 females and 10 males). Paratype designation is not valid without a holotype, thus, all individuals are syntypes ( ICZN, 1999). Inside of the tube, we saw and examined only 28 type specimens (19 females and 9 males). We failed to find the 11 remaining syntypes (in accordance with a handwritten catalog of type specimens) or two syntypes (according to the label and published list of type specimens) that were most likely lost.

Geographic distribution. Endemic to Lake Baikal. Reliable distribution is unknown, as the species was counted together with C. florensovi Mazepova, 1990 . Found in all basins of the lake at depths of 5–50 m (for details see Mazepova 1990: p. 312). Inhabits on sand and stones.

Figures

FIGURE 19. Cytherissa obrutshevi Mazepova, 1990, schematic drawings of the valves of females (A–D) and males (E–H), outer (A, B, E, F) and inner (C, D, G, H) sides, laterally. Arrows point towards the anterior. A–D—paralectotype No. 27; E–H—paralectotype No. 26. Scale 500 µm.

FIGURE 20. Cytherissa obrutshevi Mazepova, 1990, SEM photographs of carapaces (A–D) and valves (E, F) of females: A, B—laterally, outer side; C—ventrally; D—dorsally; E—LV laterally, inner side; F—RV laterally, inner side. Arrows point towards the anterior. A—paralectotype No. 18; B—paralectotype No. 19; C—paralectotype No. 21; D—paralectotype No. 20; E, F—paralectotype No. 27. Scale 500 µm.

FIGURE 21. Cytherissa obrutshevi Mazepova, 1990, SEM photographs of carapaces (A–D) and valves (E, F) of males: A, B—laterally, outer side; C—ventrally; D—dorsally; E—LV laterally, inner side; F—RV laterally, inner side. Arrows point towards the anterior. A—paralectotype No. 22; B—paralectotype No. 23; C—paralectotype No. 25; D—paralectotype No. 24; E, F—paralectotype No. 26. Scale 500 µm.

FIGURE 22. Cytherissa golyschkinae Mazepova, 1990 (A, C, D) and Cytherissa obrutshevi Mazepova, 1990 (B, E), SEM photographs of some elements of carapace (A, B) and body (C–E) structure of females (B) and males (A, C, D, E): A—central part of LV, laterally; B—central part of carapace, ventrally; C—mandible gnathobase; D, E—hemipenis. In A, B, arrows point towards the anterior. A—paralectotype No. 18; B—paralectotype No. 21; C, D—paralectotype No. 24; E—paralectotype No. 26. Scale, µm: A, B—100; C—20; D, E—200.

FIGURE 38. Microphotographs of male hemipenes of the studied species: A—Cytherissa glomerata Mazepova, 1990, paralectotype No. 19; B—Cytherissa dubitabilis (Bronstein, 1947) Mazepova 1990, specimen No. 11; C—Cytherissa derupta Mazepova, 1984, paralectotype No. 11; D—Cytherissa plena Mazepova, 1985, paralectotype No. 29; E—Cytherissa cytheriformis Bronstein, 1947, specimen No. 20; F—Cytherissa golyschkinae Mazepova, 1990, paralectotype No. 26; G— Cytherissa obrutshevi Mazepova, 1990, paralectotype No. 16; H—Cytherissa calva Mazepova, 1990, paralectotype No. 20; I—Cytherissa bisetosa Mazepova, 1984, paralectotype No. 17; J—Cytherissa sinistra Mazepova, 1984, paralectotype No. 26. Scale 100 µm.

FIGURE 39. Microphotographs of valves of the studied species: A—Cytherissa glomerata Mazepova, 1990; B—Cytherissa dubitabilis (Bronstein, 1947) Mazepova, 1990; C—Cytherissa derupta Mazepova, 1984; D—Cytherissa cytheriformis Bronstein, 1947; E—Cytherissa golyschkinae Mazepova, 1990; F—Cytherissa obrutshevi Mazepova, 1990; G—Cytherissa calva Mazepova, 1990; H—Cytherissa plena Mazepova, 1985; I—Cytherissa bisetosa Mazepova, 1984; J—Cytherissa sinistra Mazepova, 1984. Sex designations for A are as for B–J. Arrows point towards the anterior. Specimens figured are the same as those used to prepare the schematic darwings of the valves. Scale 500 µm.

FIGURE 40. Drawings of non-geniculate L5 (A), L5 endopods (B–F), geniculate L6 (G), endopods of geniculate L6 (H–P) and brush organs(Q–S) ofmales:A,G,Q—Cytherissaglomerata Mazepova,1990,paralectotype No.19;B,H—Cytherissaobrutshevi Mazepova, 1990, paralectotype No. 16; C, K—Cytherissa dubitabilis (Bronstein, 1947) Mazepova 1990, specimen No. 21; D, O—Cytherissa sinistra Mazepova, 1984, paralectotype No. 27; E, N—Cytherissa plena Mazepova, 1985, paralectotype No. 29; F, J—Cytherissa derupta Mazepova, 1984, paralectotypes Nos. 11 (F) and 22 (J); I, S—Cytherissa cytheriformis Bronstein, 1947, specimen No. 20; L—Cytherissa calva Mazepova, 1990, paralectotype No. 20; M, R—Cytherissa bisetosa Mazepova, 1984, paralectotype No. 17; P—Cytherissa golyschkinae Mazepova, 1990, paralectotype No. 26. On A–F, the arrows show clear separation (D, F) and partial fusion (A–C, E) of distal segments of non-geniculate L5. The arrangement of pseudochaetae on A is characteristic of B–F but is not drawn. Scale 100 µm.