Candona korolevae 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 : 64-73

Candona korolevae Alekseeva & Krivorotkin sp. nov.

Figs. 53B ; 57–61 ; 74B ; 75B, 75F

Type locality. Lake Baikal , east coast of Olkhon Island, coastal zone of Khurai-Khalzyn Bay ( 53°02′30 N, 107°04′11 E) .

Type material. Holotype No. O18 (female) and allotype No. O18.1 (male): dwm No. O1-080624. Paratypes Nos. 1, 2 ( two males): dwm No. O2-080624. Paratypes Nos. 3, 4 (female and male): swm No. 46. Paratype No. 5 (female): swm No. 46 (valves) and wm No. O3-080624 (limbs). Paratype No. 6 (male): swm No. 46 (valves) and wm No. O4-080624 (limbs). Paratype No. 7 (male): swm No. 46 (valve fragments) and wm No. O5-080624 (limbs). Paratypes Nos. 8–12 ( 2 females, 3 males): dwm No. O1-180625.

Holotype, allotype and paratypes Nos. 1–6 were collected in Lake Baikal , middle basin, eastern coast of Olkhon Island, in the coastal zone of Khurai-Khalzyn Bay, June 8, 2024, depth 0.3 m, stone with algae; paratype No. 7 was collected at the same locality and on the same date, but at a depth of 2 m, sand between stones . Paratypes Nos. 8–12 were collected at the same locality on June 18, 2025, depth 0.5 m, stone with algae .

Etymology. The species is named in honor of Anastasia Gennadievna Koroleva (Limnological Institute SB RAS, Irkutsk, Russia), a molecular biologist, specialist in the biology of telomeres of Baikalian hydrobionts and an excellent teacher.

Description. Female. Carapace ( Figs. 57A–57D ; 58A, 58B, 58E ; 74B ) laterally kidney-drop-shaped; L = 630– 650 µm (average 640 µm, n = 3), greatest H = 335–350 µm (average 345 µm, n = 3) located on border of posterior 1/3 of L. Dorsal margin smoothly arcuate. Anterior margin of valves widely rounded near ventral margin, posterior margin slightly sloping, drawn into an acute angle. Ventral margin smoothly curved on outer and inner sides. LV slightly overlaps RV throughout. Inner lamella relatively broad, especially in posterior part of valves. Marginal pore canals occupy 15–40% of width of inner lamella in anterior and posterior parts of valve. Inner lamella of each valve of same individual with at least 60–65 marginal pore canals. Sensillae of outer lamella relatively sparse and emerge from bordered pores. Microrelief over most of carapace smooth and homogenous. Posterior margin covered with “knitted” microrelief ( Fig. 59A–59C ), which consists of individual elements of rounded or polygonal shape. Center of these individual elements is smooth, and perimeter covered with grooves and elevations directed towards center ( Fig. 59D–59G ). Microrelief smooths out with distance from posterior margin and is replaced by shallow grooves forming rhomboid structures, which then become completely smooth. Site of greatest width (both ventrally and dorsally) poorly defined and located in central part of carapace. Carapace of living specimens is brown and does not lose its color for at least several months when preserved in ethanol.

A1 ( Fig. 60A ) seven-segmented. First segment with one plumose seta. Second segment with three setae. Third segment with one seta. Fourth segment with two setae. Fifth segment with one short seta and two long setae. Sixth segment with two claws of different lengths, two long setae and one short seta. Seventh segment with one claw, two setae of different lengths and stick-shaped aesthetasc (ya).

A2 ( Fig. 60B–60E ) five-segmented. Coxal segment with three setae, one of them inserted on this segment, two located between coxal and basal segments. One of them small and pappose. Basal segment with one ventro-distal seta. Exopod with two short smooth setae and one long seta. Endopod three-segmented. First endopodal segment with posteromedial club-shaped aesthetasc (Y) and two posterodistal setae of almost equal length. Second endopodal segment with one ventromedial seta, dorsal-medial aesthetasc (y1), three t-setae (t1 two times longer than t2 and t3); three z-setae (z1–z3); three G-claws (G1–G3) of nearly equal length and distal aesthetasc (y2). Last segment with two G-claws (GM and Gm; GM longer than Gm) and two setae, one of them basally fused with stick-shaped aesthetasc (y3).

Md ( Fig. 53B ). Coxa with one subapical seta and several setae between teeth of endite and on apical inner corner. Branchial plate with seven plumose setae and one smooth seta. Palp four-segmented. First segment with four setae: S1 (long, plumose), S2 (short, pappose), α (small and short) and proximal seta. Second segment with six posterior setae (β-seta small) and two anterior setae. Third segment with four posterodistal setae (γ-seta large, plumose) and three anterior setae. Distal segment with two claws of equal length and two setae (one of them very small).

Mxl. Protopod without setae. First endite with 14 setae, two at base of endite, 12 at apex. Second endite with nine setae. Third endite with eight setae and two claws. Palp two-segmented; first segment with four setae. Distal segment with two claws and seta apically and three setae medially. Branchial plate with 23 setae and long row of pseudochaetae.

L5 ( Fig. 61A ). Protopod with three setae (a, b, d). Endite with 14 setae, arranged in two groups of four and ten setae. Palp with three setae and rows of small pseudochaetae. Branchial plate represented by two setae of different lengths.

L6 ( Fig. 61D ) five-segmented. First through third segments with distal seta (d1, e, f) each and rows of pseudochaetae. Fourth segment with two distal g-setae and rows of pseudochaetae. Fifth segment with long claw (h2) and two setae (h1 and h3) of different lengths.

L7 ( Fig. 61E ) four-segmented. First segment with anterior d1-seta, posterior dp-seta and rows of small pseudochaetae; d2 seta absent. Second segment without pseudochaetae. Third segment with posterodistal g-seta. Fourth segment with three serrate setae (h1–h3), all of different lengths.

UR ( Fig. 61F ) symmetrical, with smoothly curved main axis, wide and tapering distally. Each ramus with one posterior seta distal to middle of ramus, one short anterodistal seta and two distal claws of different lengths.

Male. Carapace ( Fig. 57E–57H ; 58C, 58D, 58F ; 74B ) laterally kidney-shaped, same size as female; L = 625– 650 µm (average 640 µm, n = 5), greatest H = 335–350 µm (average 340 µm, n = 5). Posterior margin rounded compared to that in female. Small acute-angled outgrowth in anterior part of ventral margin formed by extension of outer fringe of valves. Inner lamella in posterior part of valves narrower compared to that of female. No microrelief in posterior part in comparison with female. Other morphological features of carapace, A1, A2 (protopod, exopod and first endopodal segment), Md, Mxl, L5 protopod, L6, L7, as in female.

A2 ( Fig. 60F–60I ) six-segmented (four-segmented endopod). Second endopodal segment with one ventromedial seta, dorsal-medial aesthetasc (y1), four t-setae (t2 and t3 modified into sensory setae with oval end, t1-seta long, t4-seta short). Third endopodal segment with three z-setae (z1 and z2 modified into long claws), three G-claws (G2 two times longer than G1 and G3), and distal aesthetasc (y2). Terminal segment with long Gm-claw, short GM-claw, and two setae, one of them basally fused with stick-shaped aesthetasc (y3).

Prehensile palps of L5 ( Fig. 61B, 61C ) asymmetrical. Both palps crescent-shaped, curved distally to site of insertion of two setae. Right palp significantly thicker than left. Distal tip of both palps with thin seta.

Hemipenis ( Fig. 75B ) rectangular, 250 µm long and 135 µm wide (including outer lobe); outer lobe shaped like truncated cone and protrudes strongly.

Zenker organ ( Fig. 75F ) 215 µm long, with 4+2 rings of spines 60 µm in diameter, central tube 25 µm in diameter, vesicle large, 50 µm in diameter.

UR ( Fig. 61G ) as in female, but rami narrower.

Comparisons. Males of the new species remotely resemble males of Candona picta Mazepova, 1990 and Candona virgata Mazepova, 1985 in carapace morphology, but differ in the morphology of the prehenhile palps and hemipenes. Females have a unique valve contour and unique microrelief. Females of C. picta and C. virgata have a slightly sloping posterior margin, but are clearly distinguishable from females of the new species.

Notes. In the process of studying the ostracod fauna of Lake Baikal, we discovered at least one more species with a microrelief similar to the females of C. korolevae sp. nov.

Geographic distribution. Endemic to Lake Baikal, found on the east coast of Olkhon Island, in the coastal zone of Khurai-Khalzyn Bay (depths of 0.3–2 m). Lives on stones with algae and on sand between stones.

Figures

FIGURE 53. Candona concava Alekseeva & Krivorotkin sp. nov. (A), Candona korolevae Alekseeva & Krivorotkin sp. nov. (B) and Candona perforata Alekseeva & Krivorotkin sp. nov. (C), drawings of Md. A—paratype No. 15; B—paratype No. 5; C—allotype. Scale 100 µm.

FIGURE 57. Candona korolevae Alekseeva & Krivorotkin sp. nov., schematic drawings of valves of female (A–D) and male (E–H), outer (A, B, E, F) and inner (C, D, G, H) sides, laterally. A–D—paratype No. 5; E–H—paratype No. 6. Scale 400 µm.

FIGURE 58. Candona korolevae Alekseeva & Krivorotkin sp. nov., SEM photographs of carapaces (E, F) and valves (A–D) of females (A, B, E) and males (C, D, F): A–D—laterally, outer side; E, F—dorsally. A, B—paratype No. 5; C, D—paratype No. 6; E—paratype No. 3; F—paratype No. 4. Scale 300 µm.

FIGURE 59. Candona korolevae Alekseeva & Krivorotkin sp. nov., SEM photographs of microrelief in posterior part of carapace (B) and valves (A, C–G) of females laterally (A, C–G) and dorsally (B). A, C–G—paratype No. 5; B—paratype No. 3. Scale, µm: A–C—100; D–G—20.

FIGURE 60. Candona korolevaeAlekseeva & Krivorotkin sp. nov., drawings of limbs of female (A–E) and male (F–I): A—A1; B—A2 without distal segment; C, E, I—distal segments of A2; D, G—fourth segment of A2; F—fourth to sixth segments; H—fifth segment of A2. A–E—paratype No. 5; F–I—paratype No. 6. Scale 100 µm.

FIGURE 61. Candona korolevae Alekseeva & Krivorotkin sp. nov., drawings of limbs of female (A, D–F) and male (B, C, G): A—L5; B—left prehensile palp of L5; C—right prehensile palp of L5; D—L6; E—L7; F, G—UR. A, D–F—paratype No. 5; B, C, G—paratype No. 7. Scale 100 µm.

FIGURE 74. Candona concava Alekseeva & Krivorotkin sp. nov. (A), Candona korolevae Alekseeva & Krivorotkin sp. nov. (B), Candona lanata Alekseeva & Krivorotkin sp. nov. (C) and Candona perforata Alekseeva & Krivorotkin sp. nov. (D), microphotographs of valves of females and males, laterally. Specimens figured are the same as those used to prepare the schematic drawings of the valves. Scale 500 µm.

FIGURE 75. Candona concava Alekseeva & Krivorotkin sp. nov. (C, G), Candona korolevae Alekseeva & Krivorotkin sp. nov. (B, F), Candona lanata Alekseeva & Krivorotkin sp. nov. (A, E) and Candona perforata Alekseeva & Krivorotkin sp. nov. (D, H), microphotographs of hemipenes (A–D) and Zenker organs (E–H). A, E—paratype No. 38; B, F—paratype No. 6; C—paratype No. 16; D, H—allotype; G—paratype No. 17. Scale 100 µm.