Cytherissa derupta Mazepova, 1984

Cytherissa derupta Mazepova, 1984

Figs. 8–11 View FIGURE 8 View FIGURE 9 View FIGURE 10 View FIGURE 11 ; 38C View FIGURE 38 ; 39C View FIGURE 39 ; 40F, 40J View FIGURE 40 .

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) GoogleMaps .

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

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 View FIGURE 8 ; 9A–9F View FIGURE 9 ; 39C View FIGURE 39 ) 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 View FIGURE 11 ). 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 View FIGURE 11 ); closer to ventral and dorsal margins, pits more smoothed ( Fig. 11C, 11D View FIGURE 11 ). Anterior ( Fig. 11B View FIGURE 11 ) 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 View FIGURE 9 ). 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 View FIGURE 8 ; 10A–10F View FIGURE 10 ; 39C View FIGURE 39 ) 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 View FIGURE 10 ) distinctly narrower than females ( Fig. 9C, 9D View FIGURE 9 ), 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 View FIGURE 40 ) 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 View FIGURE 40 ). First segment with very small, barely visible seta. Distal part of second segment with gently pointed outgrowth.

Hemipenis ( Figs. 11F View FIGURE 11 ; 38C View FIGURE 38 ) 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.