Cytherissa derupta Mazepova, 1984

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 : 312-317

Cytherissa derupta Mazepova, 1984

Figs. 8–11 ; 38C ; 39C ; 40F, 40J .

Type locality. Lake Baikal , one of two locations: 1) shallow water at the Selenga River estuary, precise location unknown (approximate coordinates 52º22’26.11” N, 106º22’09.74” E); 2) shallow water at the Selenga River estuary, opposite Sukhaya Village (approximate coordinates 52º33’49.79” N, 107º04’34.76” E) .

Type material. Lectotype No. 11 (female) and paralectotype No. 1 (male): dwm No. O1-090671. Paralectotypes Nos. 2–7 (6 females): dwm No. O2-090671. Paralectotypes Nos. 8–10 (3 males): dwm No. O3-090671. Paralectotype No. 11 (male): dwm No. O3-090671 (left valve), swm No. 20 (right valve), and wm No. O4-090671 (limbs). Paralectotypes Nos. 12–19 (4 females, 4 males): swm No. 20. Paralectotype No. 20 (female): swm No. 20 (separate body and valves). Paralectotype No. 21 (male): swm No. 20 (separate body and valves). Paralectotype No. 22 (male): swm No. 20 (valves) and wm No. O5-090671 (limbs). Paralectotype No. 23 (female): swm No. 20 (right valves) and wm No. O6-090671 (limbs). Paralectotype No. 24 (female): swm No. 20 (right valves) and wm No. O7-090671 (limbs).

All ostracods were collected from one of two locations in Lake Baikal: 1) shallow water at the Selenga River estuary, June 9, 1971, depth 38 m; 2) shallow water at the Selenga River estuary, opposite Sukhaya Village, August 3, 1983, depth 20 m and 50 m, silty sand, sample No. 1076 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. 8A–8D ; 9A–9F ; 39C ) laterally elongate-ovate: L=620–650 µm (mean 635 µm, n=10), largest H=380–410 µm (mean 400 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 near ventral margin. Ventral margins of both valves equally concave on inner side; ventral margin of LV concave on outer side as on inner side, and straight on RV. RV overlaps LV throughout except for anterior margin. Inner lamella broad. Marginal pore canals long, occupying 100% of inner lamella and ending in sensilla. Inner lamella of each valve with 13–23 marginal pore canals. Pore canals of outer lamella sieve-type, branching, grouped (up to four canals in group), single near margin of valves; each canal with one sensillum ( Fig. 11E ). Outer lamella of each valve with at least 50–65 pore canals. Inner side of each valve with approximately 30–35 canal apertures. Hinge teeth on LV, distinctly crenulated; bar on RV, crenulated. Hinge teeth on LV, distinctly crenulated; bar on RV, crenulated. Posterior hinge tooth slightly extending beyond margin of valve. Microrelief of valve surface heterogeneous, consisting of large round pits covering central part of valves ( Fig. 11A ); closer to ventral and dorsal margins, pits more smoothed ( Fig. 11C, 11D ). Anterior ( Fig. 11B ) and posterior margins of valves almost smooth. Site of greatest width of carapace on ventral and dorsal views located at posterior border of 3/4 L ( Fig. 9C, 9D ). In lateral view, site of greatest width remotely resembling rib-shaped protrusion extending from ventral margin to dorsal margin.

A1, A2, Md, Mxl, L5–L7 as in female C. heckyi .

Male. Carapace ( Figs. 8E–8H ; 10A–10F ; 39C ) slightly longer and lower than in female: L=650–680 µm (mean 670 µm, n=10), greatest H=380–400 µm (mean 390 µm, n=10). In dorsal and ventral views, males ( Fig. 10C, 10D ) distinctly narrower than females ( Fig. 9C, 9D ), site of greatest width shifted to posterior margin and located at 1/ 8 L. Inner lamella of each valve with 15 pore canals. Outer lamella of each valve with at least 70–75 pore canals. Inner side of each valve with approximately 24–32 canal apertures. Geniculate (transformed) legs on left side of body. Other morphological features of carapace structure, microrelief, A1, A2, Md, Mxl, right (nongeniculate) legs L5 ( Fig. 40F ) and L6 as in female. Both legs L7 and left (geniculate) L5 as in male C. heckyi .

L6. Left leg. Protopod with four setae and several groups of pseudochaetae. Endopod two-segmented ( Fig. 40J ). First segment with very small, barely visible seta. Distal part of second segment with gently pointed outgrowth.

Hemipenis ( Figs. 11F ; 38C ) small, triangular; outer appendage with gradually curved main axis, almost saber-shaped, tip of appendage slightly pointed. Length of hemipenis in quiescent state 310 µm (n=1), greatest width 220 µm. Diameter of copulatory process 85–90 µm.

Brush organ. Both rami with 18 apical setae, rows of pseudochaetae in subapical and apical part. Row of pseudochaetae in medial part either very fine or absent.

Differential diagnosis. By the hinge structure, C. derupta specimens are attributed to the species with teeth on the left valve. Specimens of C. derupta in dorsal and ventral views are elongate-triangular, allowing to clearly distinguish them from other Baikalian species of this genus. These traits of C. derupta make it similar to C. cytheriformis specimens but with obviously different microrelief and carapace size.

Notes. The list of type specimens ( Mazepova 2001: pp. 554) include 25 individuals: 7 paratypes (6 females and a male) and 18 syntypes (9 females and 9 males). However, the handwritten version of G.F. Mazepova’s catalog of type specimens lists only 14 (9 females and 5 males). The label on the tube indicates 25 types specimens (15 females and 10 males), which we examined. The definition of paratypes is not valid without a holotype ( ICZN, 1999), therefore, all specimens are considered syntypes.

Geographic distribution. Endemic to Lake Baikal, found in the southern basin, in shallow water at the Selenga River estuary, in the Maloye More Strait, north of the Svyatoy Nos peninsula at depths from 5 to 50 m (for details see Mazepova 1990: p. 401). Lives on sand, once recorded on stones with sponges.

Cytherissa cytheriformis Bronstein, 1947

Figs. 12–15 ; 38E ; 39D ; 40I, 40S .

Type locality. Lake Baikal , Maloye More Strait, near Ulan-Baysan Cape (second name Zantyk Cape) (approximate coordinates 53º19’24.92” N, 107º38’45.39” E) .

Type material. Neotype No. O11 (female): dwm No. O25-130868.

Additional material. Specimen No. 1 (male): dwm No. O25-130868. Specimens Nos. 2–15 (14 females): dwm No. O26-130868. Specimens Nos. 16–19 (4 males): dwm No. O27-130868. Specimen No. 20 (male): dwm No. O27-130868 (valves) and wm No. O28-130868 (limbs). Specimens Nos. 21–28 (4 females; 4 males): swm No. 19. Specimen No. 29 (male): swm No. 19 (valves) and wm No. O29-130868 (limbs). Specimen No. 30 (female): swm No. 19 (valves) and wm No. O29-130868 (limbs).

All ostracods were collected in the Maloye More Strait, near Ulan-Baysan Cape (second name Zantyk Cape), August 13, 1968, depth 10 m, sand with detritus, sample No. 174 from the collection of taxocoenoses of G.F. Mazepova.

Description. Female. Carapace ( Figs. 12A–12D ; 13A–13F ; 39D ) laterally elongate-ovate: L=935–990 µm (mean 965 µm, n=10), largest H=520–545 µm (mean 535 µm, n=10), located at 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 on inner and outer sides equally concave. RV overlaps LV on dorsal margin. Inner lamella broad. Marginal pore canals may be short and may not reach margin of inner lamella or may occupy 100% of inner lamella; some marginal pore canals branching, especially in anterior part of valves. Inner lamella of each valve with 36–39 marginal pore canals (15–17 short, 21–22 long). Pore canals of outer lamella sieve-type, branching, grouped (up to seven canals), single near margin of valves; each canal with one sensillum. Outer lamella of each valve with at least 170–180 pore canals. Inner side of each valve with about 45–47 canal apertures. Hinge teeth on LV, slightly crenulated, not extending beyond margin of valve; bar on RV, crenulated. Microrelief of valve surface heterogeneous, consisting of smoothed shallow circular pits; size of pits decreases towards dorsal and ventral margin ( Fig. 15A–15E ), dorsal margin of valve almost smooth. Anterior and posterior parts of carapace uneven due to highly smoothed pits ( Fig. 15B ). Site of greatest width of carapace on ventral and dorsal views is at posterior border of 3/4 L ( Fig. 13C, 13D ). In lateral view, site of greatest width resembling oval protrusion ( Fig. 15C ) extending from center of carapace to posterior-ventral corner.

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

Male. Carapace ( Figs. 12E–12H ; 14A–14F ; 39D ) slightly longer and lower than in female: L=1015–1065 µm (mean 1035 µm, n=10), H=495–545 µm (mean 515 µm, n=10). Site of greatest width on dorsal and ventral views shifted slightly beyond posterior 1/5 L ( Fig. 14C, 14D ). Outer lamella of each valve with at least 195–205 pore canals. Inner side of each valve with approximately 57–68 canal apertures. Geniculate (transformed) legs on left side of body. Other morphological features of carapace structure, microrelief ( Fig. 15A, 15D, 15F ), A1, A2, Md, Mxl, right (nongeniculate) legs L5 and L6 as in female; distal segments of L5 partially fused. Both legs of L7 and left (geniculate) L5 as in male C. heckyi .

L6. Left leg ( Fig. 40I ). Protopod with four setae and several groups of pseudochaetae. Endopod three-segmented. First segment with plumed seta. Distal part of endopod with gently pointed outgrowth.

Hemipenis ( Fig. 38E ) medium-sized, triangular; outer appendage triangular, slightly widened at tip. Length of hemipenis in quiescent state 395 µm (n=1), greatest width 305 µm. Diameter of copulatory process 180 µm.

Brush organ ( Fig. 40S ). Both rami with 10 apical setae, row of small pseudochaetae in medial part, rows of pseudochaetae in subapical and apical parts.

Differential diagnosis. Similar to the previous species (see differential diagnosis of C. derupta ).

Notes. As previously mentioned, Z.S. Bronstein (1930; 1947) did not distinguish type series. G.F. Mazepova identified syntypes of the species C. cytheriformis ( Mazepova 2001: pp. 551). While doing this, she isolated the “ syntypes ” from the samples taken only in 1968, i.e. 21 years after the publication of the original description. Therefore, the collection specimens cannot be regarded syntypes according to ICZN (1999). That is why we distinguish a neotype based on Mazepova’s specimens.

Geographic distribution. Endemic to Lake Baikal, found in the northern and southern basins, in the Maloye More Strait at depths from 2 to 100 m (for details see Mazepova 1990: p. 381). Inhabits sand, twice recorded on stones.

Figures

FIGURE 8. Cytherissa derupta Mazepova, 1984, 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. 20; E–H— paralectotype No. 22. Scale 500 µm.

FIGURE 9. Cytherissa derupta Mazepova, 1984, 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. 12; B—paralectotype No. 13; C—paralectotype No. 15; D—paralectotype No. 14; E, F—paralectotype No. 20. Scale 500 µm.

FIGURE 10. Cytherissa derupta Mazepova, 1984, 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. 16; B—paralectotype No. 17; C—paralectotype No. 19; D—paralectotype No. 18; E, F—paralectotype No. 22. Scale 500 µm.

FIGURE 11. Cytherissa derupta Mazepova, 1984, SEM photographs of some elements of female carapace structure (A–E) and male body (F): A—posterior part of RV; B—anterior part of RV; C—central part of carapace, dorsally; D—central part of carapace, ventrally; E—pore canals and sensilla; F—hemipenis. In A–E, arrows point towards the anterior.A, B—paralectotype No. 12; C—paralectotype No. 14; D—paralectotype No. 15; E—paralectotype No. 13; F—paralectotype No. 21. Scale, µm: A–D, F—100; E—20.

FIGURE 12. Cytherissa cytheriformis Bronstein, 1947, 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—specimen No. 30; E–H— specimen No. 29. Scale 500 µm.

FIGURE 13. Cytherissa cytheriformis Bronstein, 1947, 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—specimen No. 21; B—specimen No. 22; C—specimen No. 24; D—specimen No. 23; E, F—specimen No. 30. Scale 500 µm.

FIGURE 14. Cytherissa cytheriformis Bronstein, 1947, 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—specimen No. 25; B—specimen No. 26; C—specimen No. 28; D—specimen No. 27; E, F—specimen No. 29. Scale 500 µm.

FIGURE 15. Cytherissa cytheriformis Bronstein, 1947, SEM photographs of some elements of carapace structure of females (B, C, E) and males (A, D, F): A—dorsal margin, laterally; B—anterior part of RV, laterally; C—protrusion in posterior part of RV, laterally; D—posterior part of LV, laterally; E—central part of carapace, ventrally; F—pore canals and sensilla. Arrows point towards the anterior. A—specimen No. 25; B, C—specimen No. 21; D, F—specimen No. 26; E—specimen No. 24. Scale, µm: A–E—100; F—20.

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.