Candona lanata 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 : 73-81

Candona lanata Alekseeva & Krivorotkin sp. nov.

Figs. 62–68 ; 74C ; 75A, 75E

Type locality. Lake Baikal , coastal zone of Ayaya Bay ( 55°27′19 N, 109°53′43 E).

Type material. Holotype No. O19 ( male) and allotype No. O19.1 ( female): dwm No. O1-130624 . Paratypes Nos. 1–19 ( 19 females): dwm No. O2-130624 . Paratypes Nos. 20–26 ( 7 females): dwm No. O3-130624 . Paratypes Nos. 27–34 ( 4 females, 4 males): swm No. 44 . Paratype No. 35 ( female): swm No. 44 ( valves) and wm No. O4- 130624 ( limbs). Paratype No. 36 ( female): swm No. 44 ( valves) and wm No. O5-130624 ( limbs). Paratype No. 37 ( female): swm No. 44 ( valves) and wm No. O6-130624 ( limbs). Paratype No. 38 ( male): swm No. 44 ( valves) and wm No. O7-130624 ( limbs). Paratype No. 39 ( male): swm No. 44 ( valves) and wm No. O8-130624 ( limbs). Paratype No. 40 ( male): swm No. 44 ( valves) and wm No. O9-130624 ( limbs).

All specimens were collected in Lake Baikal, northern basin, in the coastal zone of Ayaya Bay, June 13, 2024, depth 18 m, sand and stones with algae.

Etymology. The name of the species comes from the word “lanatus” (Latin) – covered with wool, woolly and reflects the large number of pseudochaetae covering the limbs of individuals of the species.

Description. Female. Carapace ( Figs. 62A–62D ; 63A–63H ; 74C ) laterally irregularly oval-trapezoidal; L = 1065–1220 µm (average 1145 µm, n = 10), greatest H = 520–600 µm (average 570 µm, n = 10). Site of greatest H poorly expressed and 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 and smoothly rounded. Ventral margin almost straight on outer and inner sides. LV overlaps RV throughout. Inner lamella relatively narrow, widened in anterior part of valves. Marginal pore canals in anterior and posterior parts of ventral margin occupy 15–60% of width of inner lamella. Inner lamella of each valve of same individual with at least 135–140 marginal pore canals. Sensillae of outer lamella relatively sparse, more frequent in anterior and posterior parts of ventral margin, emerging from bordered pores. Outer lamella of each valve of same individual with 170–180 pore canals. Microrelief smooth and homogenous. Site of greatest width (both on ventral and dorsal sides) weakly expressed and located in central part of carapace. Carapace of living crustaceans is white-yellow and does not lose its color for at least several months when preserved in ethanol.

A1 ( Fig. 67A ) eight-segmented. First segment with one seta and rows of pseudochaetae. Second segment with three setae and row of pseudochaetae. Third segment with one seta and row of pseudochaetae. Fourth segment with one seta. Fifth and sixth segments with two long setae and one short seta each. Seventh segment with three setae (two long, one short) and two claws of different lengths. Eighth segment with two setae of different lengths, one claw and stick-shaped aesthetasc (ya).

A2 ( Fig. 65A–65D ) five-segmented. Coxal segment with three setae, one inserted on this segment, two located between coxal and basal segments. One of them small and pappose. Basal segment with one ventromedial seta and row of pseudochaetae. Exopod with three setae: two short smooth, one long (smooth or very finely plumed). Endopod three-segmented. First endopodal segment with posteromedial club-shaped aesthetasc (Y), two posteromedial setae of almost equal length, and numerous rows of pseudochaetae. Second endopodal segment with one ventromedial seta, dorsal-medial aesthetasc (y1), four t-setae (t4 slightly shorter than t1–t3); three z-setae of nearly equal length (z1–z3, z1 claw-shaped), three G-claws (G1–G3) of nearly equal length, distal aesthetasc (y2) and rows of pseudochaetae. Terminal segment with two G-claws (GM and Gm; GM slightly longer than Gm) and two setae, one of them basally fused with stick-shaped aesthetasc (y3).

Md ( Fig. 66A ). 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 (relatively long, pappose), α (small and short) and proximal seta. Second segment with six posterior setae (β-seta small), two anterior setae and rows of pseudochaetae. Third segment with four posterodistal setae (γ-seta large, smooth), three anterior setae and rows of long pseudochaetae. Distal segment with two claws of equal length, three setae (one of them very small) and rows of pseudochaetae.

Mxl ( Fig. 66B–66F ). 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. 68A ). Protopod with three setae (a, b, d) and rows of long pseudochaetae. Endite with 14 setae, arranged in two groups of four and ten setae. Palp with three setae, rows of small and long pseudochaetae. Branchial plate in form of two setae of different lengths.

L6 ( Fig. 67B ) 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. 67C ) five-segmented. First segment with anterior d1-seta, posterior dp-seta, and rows of small pseudochaetae; 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. Fifth segment with three serrate setae (h1–h3), all of different lengths.

UR ( Fig. 68D ) symmetrical, with smoothly curved rami. Each ramus with one posterior seta distal to middle of ramus, one short anterodistal seta, and two distal claws of nearly equal length.

Male. Carapace ( Figs. 62E–62H ; 64A–64H ; 74C ) laterally irregularly oval-trapezoidal, longer and higher than in female; L = 1240–1285 µm (average 1265 µm, n = 6), greatest H = 675–690 µm (average 680 µm, n = 6). Ventral margin of valves slightly more concave than in female. Posterior margin of valves slightly concave. Inner lamella in posterior part of valves slightly wider than in female, with 150–155 canals. Other morphological features of carapace, A1, A2 (protopod, exopod and first endopodal segment), Md, Mxl, L5 protopod, L6, L7, as in female.

A2 ( Fig. 65E–65H )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), and rows of pseudochaetae. Third endopodal segment with three z-setae (z1 and z2 modified into long claws), three G-claws (G2 almost 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. 68B, 68C ) asymmetrical. Both palps crescent-shaped, curved distally to site of insertion of two setae. Right palp thicker than left. Distal tip of both palps with short and thick seta.

Hemipenis ( Fig. 75A ) large, rectangular, 435 µm long and 260 µm wide (including outer lobes); lobes oval, outer lobe protrudes strongly and ends in long and spiny outgrowth.

Zenker organ ( Fig. 75E ) 380 µm long, with 5+2 rings of spines 170 µm in diameter, diameter of central tube 35 µm, vesicle small, 35 µm in diameter.

UR ( Fig. 68E ) as in female, but anterior seta slightly shorter.

Comparisons. Among Baikalian species of the genus, the female carapace shape of the new species is most similar to that of Candona modesta Mazepova, 1984 . Female shells of C. modesta are distinguished by a more pronounced site of the greatest H and a significantly lower width in dorsal view (length/width ratio – 3.35, length/ width ratio of the new species – 2.5). Average length and height of female valves of the new species (L = 1145 µm, H = 570 µm) are remarkably greater than in C. modesta (L = 830 µm, H = 410 µm). Available illustrations of C. modesta ( Mazepova 1990: p. 113, Fig. 39 ) show that the e-seta of the L6 is noticeably shorter than the third segment, while the e-seta of C. lanata sp. nov. is longer than the third segment; and the A1 setae are significantly longer. In particular, a long distal A1 seta of the individuals of C. lanata sp. nov. is five times longer that the terminal segment, whereas it is at least eight times longer than the terminal segment in C. modesta . The posterior UR seta of C. modesta females is half as long as the claws, while the UR claws and setae of the new species have similar lengths. C. modesta males have not been described so far, the type material was not identified and is absent in the ostracod collection of G.F. Mazepova (2001). C. modesta specimens were found from the mouth of the Angara River (southern basin of Lake Baikal) up to Maloye More Strait ( Mazepova 1990: pp. 113, 114), and the individuals of the new species in the northern basin, in Ayaya Bay (marked as possibly occurring in the nearshore of Frolikha Bay).

Geographic distribution. Endemic to Lake Baikal, found in the coastal zone of Ayaya Bay (depth 18 m). Lives on sand and stones with algae.

Figures

FIGURE 39. Pseudocandona olchonica Mazepova, 1990, drawings of limbs of female (A–F, I) and male (G, H, J): A—L6; B—distal segment of L6; C—L7; D—distal segment of L7; E—L5; F—armature of endite of L5; G—right prehensile palp of L5; H—left prehensile palp of L5; I, J—UR. A–F, I—paralectotype No. 23; G, H, J—paralectotype No. 24. Scale, µm: A, C, E, G–J—200; B, D, F—100.

FIGURE 62. Candona lanata 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. 35; E–H—paratype No. 38. Scale 400 µm.

FIGURE 63. Candona lanata Alekseeva & Krivorotkin sp. nov., SEM photographs of carapaces (A–D) and valves (E–H) of females: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. 27; B—paratype No. 28; C—paratype No. 30; D—paratype No. 29; E, F—paratype No. 35; G, H—paratype No. 36. Scale 500 µm.

FIGURE 64. Candona lanata 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. 31; B—paratype No. 32; C—paratype No. 34; D—paratype No. 33; E, F—paratype No. 38; G, H—paratype No. 39. Scale 500 µm.

FIGURE 65. Candona lanata Alekseeva & Krivorotkin sp. nov., drawings of limbs of female (A–D) and male (E–H): A—A2 without distal segment; B, D, H—distal segments of A2; C, F—fourth segment of A2; E—fourth to sixth segments of A2; G—fifth segment of A2. A–D—paratype No. 35; E–H—paratype No. 38. Scale 100 µm.

FIGURE 66. Candona lanata Alekseeva & Krivorotkin sp. nov., drawings of limbs of female (A) and male (B–F): A—Md; B—protopod and palp of Mxl with fragment of branchial plate; C—branchial plate of Mxl; D—first endite of Mxl; E—second endite of Mxl; F—third endite of Mxl. A—paratype No. 35; B–F—paratype No. 39. Scale 100 µm.

FIGURE 67. Candona lanata Alekseeva & Krivorotkin sp. nov., drawings of A1 (A), L6 (B) and L7 (C) of females. A–C— paratype 35. Scale 100 µm.

FIGURE 68. Candona lanata Alekseeva & Krivorotkin sp. nov., drawings of limbs of female (A, D) and male (B, C, E): A—L5; B—right prehensile palp of L5; C—left prehensile palp of L5; D, E—UR. A—paratype No. 35; B, C, E—paratype No. 38; D—paratype No. 36. 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.