Cytherissa glomerata Mazepova, 1990

Cytherissa glomerata Mazepova, 1990

Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 ; 7A–7C View FIGURE 7 , 38A View FIGURE 38 ; 39A View FIGURE 39 ; 40A, 40G, 40Q View FIGURE 40 .

Type locality. Lake Baikal , shallow water at the Selenga River estuary , north of Posol’skoye Village (approximate coordinates 52º02’39.13” N, 106º09’59.48” E; hereinafter approximate coordinates are given as the central point of the locality) or opposite Severnaya channel (approximate coordinates 52º25’28.52” N, 106º32’15.17” E). GoogleMaps

Type material. Lectotype No. O10 ( female) GoogleMaps and paralectotype No. 1 ( male): dwm No. O1-080671. GoogleMaps Paralectotypes Nos. 2–4 ( 3 females): dwm No. O2-080671 . GoogleMaps Paralectotypes Nos. 5–8 ( 4 males): dwm No. O3- 080671 . GoogleMaps Paralectotypes Nos. 9–16 ( 4 females; 4 males): swm No. 17. GoogleMaps Paralectotype No. 17 ( female): swm No. 17 (valves) and wm No. O4-080671 (limbs). GoogleMaps Paralectotype No. 18 ( female): swm No. 17 (valves) and wm No. O5- 080671 (limbs). GoogleMaps Paralectotype No. 19 ( male): swm No. 17 (valves) and wm No. O6-080671 (limbs). GoogleMaps Paralectotype No. 20 ( male): swm No. 17 (valves) and wm No. O7-080671 (limbs) GoogleMaps .

All ostracods were collected in Lake Baikal, in shallow water at the Selenga River estuary, in one of two locations: 1) opposite Severnaya channel, June 8, 1971, depth 55 m, gray silt; 2) north of Posol’skoye Village, July 12, 1974, depth 50 m, silt with sand, sample No. 695 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 particular specimen was collected from.

Description. Female. Carapace ( Figs. 1A–1D View FIGURE 1 ; 2A–2F View FIGURE 2 ; 39A View FIGURE 39 ) laterally rounded-ovate: L=1145–1220 µm (mean 1175 µm, n=10), largest H=860–930 µm (mean 895 µm, n=10), situated slightly posterior to anterior 1/3 of L. Dorsal margin slightly arcuate at center. Anterior end of carapace broadly rounded; posterior end more narrowly rounded. Central parts of ventral margin of both valves almost equally concave on inner side and arcuate on outer side. LV slightly overlaps RV in anterior and posterior parts of dorsal margin (in other parts valves are identical). Inner lamella broad. Marginal pore canals long, occupying 100% of width of inner lamella and ending in sensilla. Inner lamella of each valve with 24–25 marginal pore canals. Pore canals of outer lamella opening with branching group sieve pores (up to six canals in group), single near margin of valves; each canal ending in one sensillum. Outer lamella of each valve with 245–250 pore canals (here and in the following descriptions a minimal but accurately detected number of canals is given, their complete count is extremely difficult). Inner side of each valve with about 50–55 canal apertures. Hinge teeth on RV, relatively narrow and elongated, weakly crenulated, not extending beyond margin of valve; bar on LV, weakly crenulated. Microrelief of valve surface homogeneous, with numerous small rounded pits, differing in diameter by 2–3 times ( Fig. 7A–7C View FIGURE 7 ). Site of greatest carapace width on ventral and dorsal views weakly pronounced and located in central part of carapace ( Fig. 2C, 2D View FIGURE 2 ).

A1, A2, Md, Mxl, L5–L7 as in Cytherissa heckyi Alekseeva, Krivorotkin et Timoshkin, 2025 , but distal segments of L5 partially fused (almost as in Cytherissa pennata Mazepova, 1990 ).

Male. Carapace ( Figs. 1E–1H View FIGURE 1 ; 3A–3F View FIGURE 3 ; 39A View FIGURE 39 ) slightly longer and lower than in female: L=1205–1250 µm (mean 1225 µm, n=10), greatest H=830–885 µm (mean 855 µm, n=10). In dorsal and ventral views, males ( Fig. 3C, 3D View FIGURE 3 ) significantly narrower than females ( Fig. 2C, 2D View FIGURE 2 ), site of greatest width slightly shifted toward posterior 1/ 3 L. Dorsal margin of male valves slightly straighter. Geniculate (transformed) legs on right side of body. Other morphological features of carapace structure, microrelief ( Fig. 7A View FIGURE 7 ), A1, A2, Md, Mxl, left (nongeniculate) legs L5 and L6 as in female; distal segments of nongeniculate L5 partially fused ( Fig. 40A View FIGURE 40 ). Both legs of L7 and right (geniculate) L5 as in male C. heckyi .

L6. Right leg ( Fig. 40G View FIGURE 40 ). Protopod with four setae and several groups of pseudochaetae (at least four). Endopod two-segmented. First segment with very small seta. Distal part of second segment with small pointed outgrowth.

Hemipenis ( Fig. 38A View FIGURE 38 ) large, elongate-triangular; outer appendage long, with smoothly curved main axis, almost saber-shaped. Length of hemipenis in quiescent state 620 µm (n=1), greatest width 395 µm. Diameter of copulatory process 180–200 µm.

Brush organ ( Fig. 40Q View FIGURE 40 ). Both rami with 24 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. Owing to the round shell outline in the lateral view, C. glomerata specimens are well distinguished from other Baikal species of the genus. They slightly resemble Cytherissa dextima Mazepova, 1990 , but have a quite different pattern of valve overlap (almost equal in C. glomerata , and in C. dextima the left valve is notably larger than the right one), microrelief ( C. glomerata has numerous fine pits, C. dextima —large cells) and an average carapace size ( C. glomerata : female: L=1175 µm; H=895 µm; male: L=1225 µm; H=855 µm; C. dextima : female: L=765 µm; H=495 µm; male: L=800 µm; H=490 µm).

Notes. Besides a list of type specimens published earlier ( Mazepova 2001), we have a handwritten catalog by G.F. Mazepova, on which her publication was based. Each tube with a species was supplied by a brief label showing the number of specimens and sample number from G.F. Mazepova’s collection of taxocoenoses. Unfortunately, in some cases all three versions (the published list, handwritten catalog and label) either differ from each other or have different numbers of specimens inside the tube. Therefore, we had to examine every case in detail.

For instance, the list of type specimens of C. glomerata ( Mazepova 2001: pp. 543) indicates that the collection contains 22 paratypes ( 11 females and 11 males). The list written by hand of Prof. G.F. Mazepova contains 21 type specimens ( 10 females and 11 males). The label on the tube also has 21 specimens ( 10 females and 11 males) that we studied. When describing most of endemic Baikalian ostracods, G.F. Mazepova did not indicate holotypes, and the paratypes ( Mazepova 2001) are not valid without a holotype indication. According to article 73.2 of the International Code of Zoological Nomenclature (1999)—hereinafter, ICZN, they should be regarded syntypes that was implemented in this work.

Geographic distribution. Endemic to Lake Baikal, found in the northern and southern basins at depths of 21–1300 m (for details see Mazepova 1990: p. 323). Inhabits silty sand and silt.