Cytherissa cytheriformis Bronstein, 1947

Cytherissa cytheriformis Bronstein, 1947

Figs. 12–15 View FIGURE 12 View FIGURE 13 View FIGURE 14 View FIGURE 15 ; 38E View FIGURE 38 ; 39D View FIGURE 39 ; 40I, 40S View FIGURE 40 .

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) GoogleMaps .

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

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 View FIGURE 12 ; 13A–13F View FIGURE 13 ; 39D View FIGURE 39 ) 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 View FIGURE 15 ), dorsal margin of valve almost smooth. Anterior and posterior parts of carapace uneven due to highly smoothed pits ( Fig. 15B View FIGURE 15 ). Site of greatest width of carapace on ventral and dorsal views is at posterior border of 3/4 L ( Fig. 13C, 13D View FIGURE 13 ). In lateral view, site of greatest width resembling oval protrusion ( Fig. 15C View FIGURE 15 ) 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 View FIGURE 12 ; 14A–14F View FIGURE 14 ; 39D View FIGURE 39 ) 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 View FIGURE 14 ). 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 View FIGURE 15 ), 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 View FIGURE 40 ). 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 View FIGURE 38 ) 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 View FIGURE 40 ). 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.