Cytherissa dubitabilis ( Bronstein, 1947 ) Mazepova 1990

Cytherissa dubitabilis ( Bronstein, 1947) Mazepova 1990

Figs. 4–6 View FIGURE 4 View FIGURE 5 View FIGURE 6 ; 7D–7F View FIGURE 7 , 38B View FIGURE 38 ; 39B View FIGURE 39 ; 40C, 40K View FIGURE 40 .

Type locality. Lake Baikal , shallow water at the Selenga River estuary, more precise location unknown (approximate coordinates 52º22’26.11” N, 106º22’9.74” E) GoogleMaps .

Type material. Neotype No. O1 (female): dwm No. O37-300771 GoogleMaps .

Additional material. Specimen No. 1 (male): dwm No. O37-300771. Specimens Nos. 2–4 ( 3 females): dwm No. O38-300771. Specimen No. 5 (female): dwm No. O38-300771 (valves) and wm No. O40-300771 (limbs). Specimens Nos. 6–10 ( 5 males): dwm No. O39-300771. Specimen No. 11 (male): dwm No. O39-300771 (valves) and wm No. O41-300771 (limbs). Specimens Nos. 12–19 ( 4 females; 4 males): swm No. 12. Specimen No. 20 (female): swm No. 12 (valves) and wm No. O42-300771 (limbs). Specimen No. 21 (male): swm No. 12 (valves) and wm No. O43-300771 (limbs) .

All ostracods were collected in shallow water at the Selenga River estuary, July 30, 1971, depth 8 m, silty sand with macrophytes, sample No. 320 from the collection of taxocoenoses of G.F. Mazepova.

Description. Female. Carapace ( Figs. 4A–4D View FIGURE 4 ; 5A–5F View FIGURE 5 ; 39B View FIGURE 39 ) laterally elongate-ovate: L=1010–1060 µm (mean 1035 µm, n=10), largest H=600–645 µm (mean 625 µm, n=10), located on posterior border of anterior 1/ 3 L. Dorsal margins of valves slightly arched at center. Anterior end of carapace broadly rounded, posterior end almost straight, narrowly rounded. Ventral margins of both valves equally concave on inner side and arcuately curved on outer side. LV overlaps RV on dorsal margin. Inner lamella relatively narrow. Marginal pore canals may be long, occupy 100% of width of inner lamella, or open earlier. Inner lamella of each valve with 36–39 marginal pore canals (22 long and 15–17 short). Pore canals of outer lamella sieve-type, branching, grouped (up to six canals in group), near margin of valves single; each canal with one sensillum ( Fig. 7E View FIGURE 7 ). Outer lamella of each valve with 250–290 pore canals. Inner side of each valve with 60–70 canal apertures. Hinge teeth on RV, weakly crenulated, not extending beyond margin of valve; bar on LV, weakly crenulated. Microrelief of valve surface heterogeneous, with different diameter round and oval shallow pits ( Fig. 7D, 7F View FIGURE 7 ) covering whole carapace except smooth dorsal margin. Site of greatest carapace width on ventral and dorsal views is at posterior border 3/4 L ( Fig. 5C, 5D View FIGURE 5 ).

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

Male. Carapace ( Figs. 4E–4H View FIGURE 4 ; 6A–6F View FIGURE 6 ; 39B View FIGURE 39 ) slightly longer and lower than in female: L=1045–1150 µm (mean 1120 µm, n=10), H=580–640 µm (mean 610 µm, n=10). In dorsal and ventral views, males ( Fig. 6C, 6D View FIGURE 6 ) distinctly narrower than females ( Fig. 5C, 5D View FIGURE 5 ), site of greatest width weaklier pronounced and located slightly posterior to 3/ 4 L. Posterior margin of carapace rounded. Geniculate (transformed) legs on right side of body. Other morphological features of carapace structure, microrelief, A1, A2, Md, Mxl, left (non-geniculate) legs L5 ( Fig. 40C View FIGURE 40 ) and L6 as in female. Both legs L7 and right (geniculate) leg L5 as in male C. heckyi .

L6. Right leg. Protopod with four setae and several groups of pseudochaetae. Endopod two-segmented ( Fig. 40K View FIGURE 40 ); first segment with small seta; distal part of second segment with pointed outgrowth.

Hemipenis ( Fig. 38B View FIGURE 38 ) large, triangular; outer appendage in form of broad robust triangle with slightly curved tip. Length of hemipenis in quiescent state 495 µm (n=1), greatest width 375 µm. Diameter of copulatory process 235 µm.

Brush organ. Both rami with 13 apical setae, row of small pseudochaetae in medial part, row of pseudochaetae in subapical part and barely visible row of pseudochaetae in apical part.

Differential diagnosis. The shells of C. dubitabilis specimens on the lateral and dorsal views slightly resemble Cytherissa elongata elongata Bronstein, 1947 . The species are distinguished by the shell outlines in lateral view (notably more assymentrical in C. dubitabilis ), location of wedge-shaped constriction in dorsal view in females ( C. dubitabilis in posterior part, C. elongata elongata in anterior part of the body), size ( C. dubitabilis , female: L=1135 µm; H=625 µm; male: L=1120 µm; H=610 µm; C. elongata elongata , female: L=850 µm; H=450 µm; male: L=955 µm; H=460 µm).

Notes. The species was initially described by Z.S. Bronstein as Cytherissa lacustris var. dubitabilis Bronstein, 1947 . In 1990, G.F. Mazepova pointed out that the specimens of this taxon were remarkably distinguished from Cytherissa lacustris ( Sars, 1863) by the carapace morphology and defined it as a separate species— Cytherissa dubitabilis Bronstein, 1947 . In the work of Meisch et al. (2024), we find the species name: Cytherissa dubitabilis ( Bronstein, 1947) Martens & Savatenalinton 2011 .

Z.S Bronstein (1930; 1947) did not separate type series of Baikal ostracods. G.F. Mazepova (1990) indicated syntypes of C. dubitabilis species ( Mazepova 2001: pp. 541). The sample these “ syntypes ” were taken from, was collected only in 1971, i.e. in 24 years after the publication of the original description (Z.S. Bronstein collected the samples for the description from about 1927–1928). Thus, the specimens from the collection cannot be syntypes according to ICZN (1999). Therefore, we isolate a neotype based on G.F. Mazepova’s specimens.

Geographic distribution. Endemic to Lake Baikal, found in all basins and in the Maloye More Strait at depths from 2 to 95 m (for details see Mazepova 1990: p. 309). Inhabits sands, rarely algae thickets and stones.