Candona perforata 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 : 81-89

Candona perforata Alekseeva & Krivorotkin sp. nov.

Figs. 53C , 69–73 ; 74D ; 75D, 75H

Type locality. Lake Baikal , coastal zone of Dagarskaya Bay ( 55°39′10 N, 109°54′47 E) .

Type material. Holotype No. O20 (female): dwm No. O1-200924. Allotype No. O20.1 (male): swm No. 45 (valves) and wm No. O2-200924 (limbs). Paratypes Nos. 1–4 ( 4 females): swm No. 45. Paratype No. 5 (female): swm No. 45 (valves) and wm No. O3-200924 (limbs). Paratype No. 6 (female): dwm No. O4-200924.

Additional material. Juvenile stage No. 1: swm No. 45.

All specimens were collected in Lake Baikal, northern basin, in the coastal zone of Dagarskaya Bay, September 20, 2024, depth 12 m, sand with detritus.

Etymology. The name of the species comes from the word “perforatus” (Latin) – perforated, covered with holes, indicating the distinctive microrelief of the valve surface.

Description. Female. Carapace ( Figs. 69A–69D ; 70A–70F ; 74D ) laterally elongated-trapezoidal; L = 750–780 µm (average 760 µm, n = 6), greatest H = 415–425 µm (average 420 µm, n = 6) located on border of posterior 1/4 of L. Dorsal margin almost straight.Anterior margin of valves widely rounded near ventral margin, posterior margin slightly sloping, smoothly rounded. Ventral margin smoothly concave on outer and inner sides. LV overlaps RV throughout. Inner lamella relatively broad. Marginal pore canals occupy 30–100% of width of inner lamella. Inner lamella of each valve of same individual with at least 90–100 marginal pore canals. Sensillae of outer lamella relatively sparse, more frequent in anterior and posterior parts of ventral margin( Fig.71A,71B ),emerging from bordered pores with outgrowth ( Fig. 71E ). Outer lamella of each valve of same individual with 90–105 pore canals. Microrelief complex, consisting of relatively large, smoothed pits in central part of valves ( Fig. 71C ). Rest of valve surface appears smooth ( Fig. 71A ), but on close examination it is covered with very small pits ( Fig. 71E–71G ). Entire carapace on outer side covered with numerous small blind holes ( Fig. 71G ). Homogenous microrelief imprints on inner side of both valves ( Fig. 71D ). This probably indicates a reduction in microrelief on the valve surface while preserving its imprints on inner side. Site of greatest width (both on ventral and dorsal sides) weakly expressed and located in posterior 1/3 of L. Carapace of living specimens is whitish in color and does not lose its color for at least several months when preserved in ethanol.

A1 ( Fig. 72A ) eight-segmented. First segment with one seta. Second segment with three setae. Third and fourth segments with one seta each. Fifth and sixth segments with two long setae and one claw each. Seventh segment with two setae and two claws. Eighth segment with two setae of different lengths, one claw and stick-shaped aesthetasc (ya).

A2 ( Fig. 72B, 72C ) 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 three setae: two short smooth, one long and medially plumose. Endopod three-segmented. First endopodal segment with posteromedial club-shaped aesthetasc (Y), two posterodistal setae of different lengths and rows of pseudochaetae. Second endopodal segment with one ventromedial seta, dorsal-medial aesthetasc (y1), three t-setae (t1–t3); three z-setae (z1 two times shorter than z2 and z3); three G-claws (G2 two times shorter than G1 and G3) and distal aesthetasc (y2). Terminal segment with two G-claws (GM and Gm) of almost equal length and two setae, one of them basally fused with stick-shaped aesthetasc (y3).

Md ( Fig. 53C ). 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 five posterior setae (β-seta very small), two anterior setae and rows of pseudochaetae. Third segment with four posterodistal setae (γ-seta large, smooth) and three anterior setae. Distal segment with two claws of equal length and three setae (one of them 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 and rows of pseudochaetae. Distal segment with two claws and seta apically and three setae medially. Branchial plate with 23 setae and long row of pseudochaetae.

L5 ( Fig. 73D ). 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 reduced to two setae of different lengths.

L6 ( Fig. 73A ) five-segmented. First segment with d1-seta. Second and third segments with distal seta (e, f) each and rows of small pseudochaetae. Fourth segment with two distal g-setae and rows of pseudochaetae. Fifth segment with strong long claw (h2) and two setae (h1 and h3) of different lengths.

L7 ( Fig. 73B, 73C ) five-segmented. First segment with anterior d1-seta, posterior dp-seta; d2 seta absent. Second segment with rows of small pseudochaetae. Third segment without pseudochaetae. Fourth segment with posterodistal g-seta and rows of small pseudochaetae. Third and fourth segments incompletely separated (separated on inner side, and partially fused on outer side). Fifth segment with three serrate setae (h1–h3) of different lengths.

UR ( Fig. 73H ) symmetrical, with smoothly curved main axis. Each ramus with one posterior seta distal to middle of ramus, one short anterodistal seta and two thick distal claws of almost equal length.

Male. Carapace ( Figs. 69E–69H ; 70G, 70H ; 74D ) laterally elongated-trapezoidal, longer and slightly lower than that of female; L = 780 µm, greatest H = 415 µm. Carapaces of females and males differ very slightly, but testes and ovaries are clearly visible through valves. Inner lamella of each valve with 75–80 marginal pore canals. Other morphological features of carapace, A1, A2 (protopod, exopod and first endopodal segments), Md, Mxl, L5 protopod, L6, L7, as in female.

A2 ( Fig.72D–72G ) six-segmented(four-segmented endopod).Second endopodal segment with one ventromedial seta, dorsal-medial aesthetasc (y1), three t-setae (t2 and t3 modified into sensory setae with oval ends). Third endopodal segment with three z-setae (z2 modified into long claw), three G-claws (G2 2.5 times longer than G1 and G3) and distal aesthetasc (y2). Last 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. 73E, 73F ) asymmetrical. Both palps long, straight proximally to site of insertion of two setae, and crescent-curved distally. Right palp significantly thicker than left. Distal tip of both palps with short and thick seta.

Hemipenis ( Fig. 75D ) large, rectangular, 300 µm long and 125 µm wide; lobes oval.

Zenker organ ( Fig. 75H ) 245 µm long, with 5+2 rings of spines 80 µm in diameter, diameter of central tube 30 µm, vesicle large, 55 µm in diameter.

UR ( Fig. 73G ) as in female, but claws slightly thinner, and rami straighter.

Juvenile stages very similar to adult individuals in carapace morphology ( Fig. 70I ).

Comparisons. Generally, the shell morphology of the new species resembles Candona limpida Mazepova, 1984 and Candona digitata Mazepova, 1990 . Valves of the three species have unique outlines. Sexual dimorphism of the valves of C. perforata sp. nov. is not observed, while the female and male valves of C. limpida and C. digitata are remarkably different. The A1, A2, L5, and UR of C. digitata are extremely peculiar and well distinguished from those of the new species. The UR of C. limpida females and males bear long thin claws (their length is almost half of the ramus length), and the posterior seta is half as long as the claws. Female and male UR of C. perforata sp. nov. have short and thick claws (their length is almost 1/3 of the ramus length), and the posterior seta is longer than the claws. The male prehensile palps of C. limpida , distal to the attachment place of two setae, are much longer and thinner than in the new species. The hemipenes show different morphologies; the drawings ( Mazepova 1990: p. 110: Fig. 38O ) show that the inner ducts of C. limpida hemipenes are much more proximal than in C. perforata sp. nov.

Geographic distribution. Endemic to Lake Baikal, found in the coastal zone of Dagarskaya Bay (depth 12 m). Lives on sand with detritus.

Figures

FIGURE 38. Pseudocandona olchonica Mazepova, 1990, drawings of A2 (A) and distal segments of A2 (B–F) of female (A, C, D) and male (B, E, F): A, B, D, F—outer side; C, E—inner side.A, C, D—paralectotype No. 23; B, E, F—paralectotype No. 24. On C–F, some setae and claws are shortened. Scale, µm: A, B—200; C–F—100.

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 69. Candona perforata 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—allotype. Scale 400 µm.

FIGURE 70. Candona perforata Alekseeva & Krivorotkin sp. nov., SEM photographs of carapaces (A–D, I) and valves (E–H) of females (A–F), males (G, H) and juvenile stage (I): A, B, G–I—laterally, outer side; C—ventrally; D—dorsally; E—LV laterally, inner side; F—RV laterally, inner side. A—paratype No. 1; B—paratype No. 2; C—paratype No. 4; D—paratype No. 3; E, F—paratype No. 5; G, H—allotype; I—specimen No. 1. Scale 400 µm.

FIGURE 71. Candona perforataAlekseeva & Krivorotkin sp. nov., SEM photographs of some elements of carapaces of females (A–E) and male (F, G): A—anterior part, laterally; B—anterior part, ventrally; C—central part of RV, laterally; D—central part of LV inner side, laterally; E, F—sensillae and microrelief; G—finely pitted microrelief and numerous blind holes. A, C, E—paratype No. 1; B—paratype No. 4; D—paratype No. 5; F, G—allotype. Scale, µm: A–D—100; E, F—20; G—10.

FIGURE 72. Candona perforata Alekseeva & Krivorotkin sp. nov., drawings of limbs of female (B, C) and male (A, D–G): A—A1; B—A2 without distal segment; C, G—distal segments of A2; D—fourth to sixth segments of A2 and distal part of third segment; E—fourth segment of A2; F—fifth segment of A2. A, D–G—allotype; B, C—paratype No. 5. Scale 100 µm.

FIGURE 73. Candona perforata Alekseeva & Krivorotkin sp. nov., drawings of limbs of female (A, D, H) and male (B, C, E –G): A—L6; B—L7; C—unclear separation of third and fourth segments of L7 on other side; D—L5; E—left prehensile palp of L5; F—right prehensile palp of L5; G, H—UR. A, D, H—paratype No. 5; B, C, E–G—allotype. 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.