Cytherissa golyschkinae 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 : 322-324

Cytherissa golyschkinae Mazepova, 1990

Figs. 16–18 ; 22A, 22C, 22D ; 38F ; 39E ; 40P .

Type locality. Lake Baikal , Angara River source, Listvennichny Bay , Listvyanka Settlement , opposite the building of the Baikal Museum of the Siberian Branch of the Russian Academy of Sciences (approximate coordinates 51º52’03.76’’ N, 104º49’50.57’’ E) .

Type material. Lectotype No. O12 (female) and paralectotype No. 1 (male): dwm No. O1-020368. Paralectotypes Nos. 2–6 (5 females): dwm No. O2-020368. Paralectotypes Nos. 7–13 (7 males): dwm No. O3- 020368. Paralectotypes Nos. 14–21 (4 females, 4 males): swm No. 28. Paralectotype No. 22 (female): swm No. 28 (valves). Paralectotype No. 23 (male): swm No. 28 (valves). Paralectotype No. 24 (male): swm No. 28 (valves and limbs). Paralectotype No. 25 (female): swm No. 28 (valves) and wm No. O4-020368 (limbs). Paralectotype No. 26 (male): swm No. 28 (valves) and wm No. O5-020368 (limbs). Paralectotype No. 27 (male): swm No. 28 (valves) and wm No. O6-020368 (limbs).

All ostracods were collected near the source of the Angara River, Listvennichny Bay, Listvyanka Settlement, opposite the building of the Baikal Museum, March 2, 1968, depth 3–3.5 m, stones, samples Nos. 105 and 106 from the collection of taxocoenoses of G.F. Mazepova.

Description. Female. Carapace ( Figs. 16A–16D ; 17A–17F ; 39E ) laterally rectangular-ovate: L=1015–1040 µm (mean 1025 µm, n=10), largest H=625–650 µm (mean 635 µm, n=10), located on posterior border of anterior 1/ 3 L. Dorsal margins of valves slightly arcuate at center. Anterior end of carapace broadly rounded, posterior end almost straight, narrowly rounded. Ventral margins of both valves equally concave on inner side. Ventral margin of RV concave on outer side as on inner side, but on LV almost straight, weakly concave. LV slightly overlaps RV throughout except posterior part of ventral margin. Small protrusion at posterior part of ventral margin of RV. Inner lamella broad. Marginal pore canals long, occupying 80–100% of the width of the inner lamella and ending in sensilla. Inner lamella of each valve with 32–34 marginal pore canals. Pore canals of outer lamella sieve-type, branching, grouped (up to four canals in a group), single near margin of valves; each canal with one sensillum. Outer lamella of each valve with at least 85–90 pore canals. Inner side of each valve with approximately 38–44 canal apertures. Teeth of hinge on RV, slightly crenulated, not extending beyond margin of valves; bar on LV, slightly crenulated. Microrelief of valves surface consists of evenly distributed smoothed shallow round pits ( Fig. 22A ). Examination of SEM photographs of females and males gives impression that pitted microrelief on LV slightly more pronounced ( Figs. 17B ; 18B ), and on RV smoothed ( Figs. 17A ; 18A ). Near margins of valves, pits smaller in size. Site of greatest carapace width on ventral and dorsal views weakly pronounced and located in central part of L ( Fig. 17C, 17D ).

A1, A2, Md ( Fig. 22C ), Mxl, L5–L7 as in C. heckyi , but distal segments of L5 partially fused.

Male. Carapace ( Figs. 16E–16H ; 18A–18F ; 39E ) slightly longer and lower than in female: L=1015–1065 µm (mean 1045 µm, n=10), H=570–625 µm (mean 595 µm, n=10). Posteroventral protrusion more pronounced than in female, especially on ventral view ( Fig. 18C ). 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; distal segments of L5 partially fused. Both legs of L7 and right (geniculate) L5 as in male C. heckyi .

L6. Right leg. Protopod with four setae and several groups of pseudochaetae. Endopod two-segmented ( Fig. 40P ). First segment with seta. Distal part of second segment with gently pointed outgrowth.

Hemipenis ( Figs 22D ; 38F ) triangular; outer appendage triangular, with pointed tip. Length of hemipenis in quiescent state 505 µm (n=1), greatest width 325 µm. Diameter of copulatory process 195–225 µm. Hemipenis of paralectotype No. 26 ( Fig. 38F ) and paralectotype No. 24 ( Fig. 22D ) differ slightly in structure of outer appendage, which on whole mount with pointed tip.

Brush organ. Both rami with 12 apical setae, row of small pseudochaetae in medial part, rows of pseudochaetae in subapical and apical parts.

Differential diagnosis. The shells of C. golyschkinae and C. obrutshevi are morphologically nearly identical, except for the valve outlines in lateral view and carapace outlines in dorsal and ventral views. The species differ in the segmentation of the distal L5, L6 and L7 segments in females and males: the distal segments of C. golyschkinae are partially fused only on the L5 (in females and non-geniculate in males), C. obrutshevi has partially fused distal L5–L7 segments in females and non-geniculate L5 and L 6 in males.

Notes. The list of types specimens ( Mazepova 2001: pp. 542) includes 28 paratypes (13 females and 15 males) that is in accordance with the handwritten type catalog and the label inside the tube. The designation of paratypes is not valid without the holotypes, hence, all the individuals are syntypes. Inside of the tube, we found 12 females and 16 males.

Morphological redescription of the species is especially urgent due to the publication of Schön et al. (2017) reporting of at least three different C. golyschkinae and one C. cf. golyschkinae dwelling in Baikal.

Geographic distribution. Endemic to Lake Baikal, found in all three basins and in the Maloye More Strait at depths from 5 to 50 m (for details see Mazepova 1990: p. 318). Inhabits different substrates, but more often on stones with sponges and algae.

Figures

FIGURE 16. Cytherissa golyschkinae 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. 22; E–H—paralectotype No. 23. Scale 500 µm.

FIGURE 17. Cytherissa golyschkinae 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. 15; B—paralectotype No. 14; C—paralectotype No. 17; D—paralectotype No. 16; E, F—paralectotype No. 22. Scale 500 µm.

FIGURE 18. Cytherissa golyschkinae 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. 19; B—paralectotype No. 18; C—paralectotype No. 21; D—paralectotype No. 20; E, F—paralectotype No. 23. 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.