Pseudocandona geminata Alekseeva & Krivorotkin, 2025

Alekseeva, Tatyana M., Krivorotkin, Roman S. & Timoshkin, Oleg A., 2025, New and poorly known species of family Candonidae (Crustacea, Ostracoda, Podocopida) from Lake Baikal, Zootaxa 5734 (1), pp. 1-91 : 54-59

Pseudocandona geminata Alekseeva & Krivorotkin sp. nov.

Figs. 44–48

Type locality. Lake Baikal , coastal zone opposite Elokhin Cape (approximate coordinates: 54°32′42 N, 108°39′42 E) .

Type material. Holotype No. O21 (male) and allotype No. O21.1 (female): dwm No. O3-200776. Paratypes Nos. 1–35 ( 12 females, 23 males): dwm No. O4-200776. Paratypes Nos. 36–41 (three pairs of females and males in copula): dwm No. O5-200776. Paratypes Nos. 42–50 ( four females, five males): swm No. 51. Paratype No. 51 (female): swm No. 51 (valves) and wm No. O6-200776 (limbs). Paratype No. 52 (female): swm No. 51 (valves) and wm No. O7-200776 (limbs). Paratype No. 53 (male): swm No. 51 (valves) and wm No. O8-200776 (limbs). Paratype No. 54 (male): swm No. 51 (valves) and wm No. O9-200776 (limbs). Paratype No. 55 (male): swm No. 51 (valves) and wm No. O10-200776 (limbs). Paratype No. 56 (male): swm No. 51 (valves and Zenker organ). Paratypes Nos. 57–60 (two pairs of females and males in copula): swm No. 51. Paratypes Nos. 61, 62 ( two males): swm No. 51.

All specimens were collected in Lake Baikal, northern basin, in the coastal zone opposite Elokhin Cape, July 20, 1976, depth 5 m, sand with algae (genus Draparnaldia Bory de Saint-Vincent, 1808 ), sample No. 743 from the collection of G.F. Mazepova.

Etymology. The name of the species comes from the word “geminatus” (Latin) – double, paired and is associated with the identical location of two small ventral projection on the male carapaces.

Description. Female. Carapace ( Figs. 44E–44H ; 45A–45F ; 48A, 48B ) trapezoidal; L = 960–1015 µm (average 985 µm, n = 10), greatest H = 570–600 µm (average 580 µm, n = 10) located slightly anteriorly to anterior 1/3 of L. Dorsal margin straight, anterior margin widely rounded, posterior margin in form of obtuse angle. LV overlaps RV throughout. Ventral margin of both valves less concave on outer side than on inner side. Inner lamella broad, marginal pore canals occupy 70–100% of inner lamella width. Inner lamella of each valve with at least 40–45 marginal pore canals. Sensillae of outer lamella relatively sparse. Microrelief of valve surface homogenous ( Fig. 47A ), consisting of cells. Diameter of cells larger in center and slightly smaller at margins of valves. Site of greatest width (both ventrally and dorsally) slightly behind center L of carapace.

A1, A2, Md, Mxl, L5, L7, and UR as in female P. glauci .

Male. Carapace ( Figs. 44A–44D ; 46A–46H ; 48C, 48D ) trapezoidal, slightly shorter and lower than in female; L = 910–960 µm (average 925 µm, n = 10), greatest H = 520–570 µm (average 550 µm, n = 10) located slightly behind posterior 1/3 of L. Dorsal margin straight, slightly inclined toward anterior end, anterior margin rounded, posterior end slightly sloping, without distinct angle region as in female. Ventral margin of carapace with two symmetrical projections (one on each valve, Fig. 47B–47E ), which located slightly behind center of L, in posterior part of ventral concavity. Length of projections 40–50 µm, base width 50–60 µm. Main axis of both projections directed backwards and slightly towards opposite valve. Central part of ventral margin of valves on inner side more concave than in female. Dorsally and ventrally, carapace narrower than in female, site of greatest width expressed less clearly. Other morphological features of carapace structure, A1, A2 (protopod, exopod and first endopodal segment), Md, Mxl, L5 protopod, L6, L7 as in female. Second and third endopodal segments of A2 and UR as in male P. glauci .

Prehensile palps of L5 ( Fig. 48G, 48H ) almost symmetrical, crescent-shaped and resembling palps of P. glauci male, but curved more sharply, and distal end of left palp noticeably wider.

Hemipenis ( Fig. 48E ) rounded-rectangular, 305 µm long and 180 µm wide; lobes oval, weakly protruding.

Zenker organ ( Figs. 47H ; 48F ) 285 µm long, with 4+2 rings of spines 100 µm in diameter, diameter of central tube 43 µm, vesicle large, 75 µm in diameter.

Comparisons. The carapace and soft body morphologies of males and females of P. geminata sp. nov. are very similar to those of P. glauci . There are two symmentrically located projections (one on each valve) on the ventral side of the male carapace of the new species, while P. glauci males have four ventral projections (two on each valve). Comparions of the valve outlines of the male and female individuals demonstrate differences of the posterior margin. It is clearly seen in SEM images of the inner side of the valves: the posterior margin of P. glauci females is more rounded ( Fig. 28E, 28F ), whereas this margin has a well-defined angle in females of the new species ( Fig. 45E, 45F ). The shape of the posterior valve margin of the males (besides ventral projections) is different: it is more rounded in P. glauci ( Fig. 29E, 29F ), and more angular in P. geminata sp. nov. ( Fig. 46E, 46F ). The inner side of the ventral margin of males of the new species is more concave than in males of the previously described species. The prehensile palps of the L5 of P. geminata sp. nov. males differ from P. glauci male palps by a sharper curve of the main axis and a wider distal part of the left palp ( Figs. 32F, 32G ; 48G, 48H ). Hemipenes of the species compared show a similar morphology, but the outer lobe of the new species is somewhat longer. Judging by the females and males during copulation, the species mate in various positions: P. glauci males grasp the ventro-posterior tip of the female shell with four ventral projections ( Fig. 43C, 43D ), but P. geminata sp. nov. males fix much higher on the posterior margin ( Fig. 47F, 47G ).

Geographic distribution. Endemic to Lake Baikal, found in the coastal zone opposite Elokhin Cape (depth 5

m). Lives on sand with algae.

Genus Candona Baird, 1845

Figures

FIGURE 28. Pseudocandona glauci Mazepova, 1990, 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. A—paralectotype No. 13; B—paralectotype No. 12; C—paralectotype No. 15; D—paralectotype No. 14; E, F—specimen No. 2. Scale 400 µm.

FIGURE 29. Pseudocandona glauci Mazepova, 1990, 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. A—paralectotype No. 17; B—paralectotype No. 18; C—paralectotype No. 20; D—paralectotype No. 19; E, F—specimen No. 3. Scale 400 µm.

FIGURE 32. Pseudocandona glauci Mazepova, 1990, drawings of limbs of female (A–E, H) and male (F, G, I): A—L6; B—L7; C—L5; D, E—groups of distal setae of L5; F—left prehensile palp of L5; G—right prehensile palp of L5; H, I—UR. A–E, H—paralectotype No. 24; F, G, I—paralectotype No. 25. Scale 100 µm.

FIGURE 43. Pseudocandona grygieri Alekseeva & Krivorotkin sp. nov. (A, B), Pseudocandona glauci Mazepova, 1990 (C, D) and Pseudocandona olchonica Mazepova, 1990 (E), females and males in copula, laterally.A, B—paratypes Nos. 79, 80; C, D—paralectotypes Nos. 22, 23; E—specimens Nos. 3, 4. Scale 500 µm.

FIGURE 44. Pseudocandona geminata Alekseeva & Krivorotkin sp. nov., schematic drawings of valves of male (A–D) and female (E–H), outer (A, B, E, F) and inner (C, D, G, H) sides, laterally. A–D—paratype No. 53; E–H—paratype 51. Scale 400 µm.

FIGURE 45. Pseudocandona geminata Alekseeva & Krivorotkin sp. nov., 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. A—paratype No. 43; B—paratype No. 42; C—paratype No. 45; D—paratype No. 44; E, F—paratype No. 51. Scale 500 µm.

FIGURE 46. Pseudocandona geminata Alekseeva & Krivorotkin sp. nov., SEM photographs of carapaces (A–D) and valves (E–H) of males:A, B—laterally, outer side; C—ventrally; D—dorsally; E—LV laterally, inner side; F—RV laterally, inner side; G—LV dorsally; H—RV dorsally. A—paratype No. 47; B—paratype No. 46; C—paratype No. 49; D—paratype No. 48; E, F—paratype No. 53; G, H—paratype No. 54. Scale 500 µm.

FIGURE 47. Pseudocandona geminata Alekseeva & Krivorotkin sp. nov., SEM photographs of some structural elements: A— microrelief in center of LV, laterally; B, C—ventral projections, laterally, outer side; D, E—ventral projections, laterally, inner side; F, G—pairs of females and males in copula; H—Zenker organ. A—paratype No. 42; B—paratype No. 47; C—paratype No. 46; D, E—paratype No. 53; F—paratypes Nos. 59, 60; G—paratypes Nos. 57, 58; H—paratype No. 56. Scale, µm: A–E, H—100; F, G—500.

FIGURE 48. Pseudocandona geminata Alekseeva & Krivorotkin sp. nov., microphotographs (A–F) and drawings (G, H) of some structural elements of female (A, B) and males (C–H): A–D—valves, laterally, outer side; E—hemipenis; F—Zenker organ; G—left prehensile palp of L5; H—right prehensile palp of L5. A, B—paratype No. 51; C, D—paratype No. 53; E–H— paratype No. 53. Scale, µm: A–D—500; E, F—100.