Pseudocandona olchonica Mazepova, 1990

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 : 42-54

Pseudocandona olchonica Mazepova, 1990

Figs. 33–39 ; 40F ; 41A ; 42F ; 43E

Type locality. Lake Baikal , east coast of Olkhon Island, coastal zone opposite Izhimey Cape (approximate coordinates: 53°13′55 N, 107°44′13 E) .

Type material. Lectotype No.O4 (male)and paralectotype No.1 (female):dwm No.O12-260969. Paralectotypes Nos. 2–8 ( 4 females, 3 males): dwm No. O13-260969. Paralectotypes Nos. 9–14 ( 4 females, 2 males): dwm No. O18-260969. Paralectotypes Nos. 15–22 ( 4 females, 4 males): swm No. x944. Paralectotype No. 23 (female): swm No. x944 (valves) and wm No. O14-260969 (limbs). Paralectotype No. 24 (male): swm No. x944 (valves) and wm No. O15-260969 (limbs).

Additional material. Specimens Nos. 1–4 ( 2 females, 2 males): swm No. x964. Specimen No. 5 (female): swm No. x964 (valves) and wm No. O16-260969 (limbs). Specimen No. 6 (male): swm No. x964 (valves) and wm No. O17-260969 (limbs). Specimens Nos. 7, 8 (males): swm No. x970.

All specimens were collected in Lake Baikal, middle basin, east coast of Olkhon Island, in the coastal zone opposite Izhimey Cape, September 26, 1969, depth 90 m, fine-grained sand, sample No. 228 from the collection of G.F. Mazepova.

Description. Female. Carapace ( Figs. 33A–33D ; 34A–34F ; 40F ) trapezoidal; L = 1870–1950 µm (average 1920 µm, n = 9), greatest H = 1180–1210 µm (average 1195 µm, n = 9) located on border of anterior 1/4 of L. Dorsal margin straight, slightly inclined toward the posterior end, anterior margin widely rounded, posterior margin slightly sloping. Dorsal margin of LV with small keel ( Fig. 34E ). LV overlaps RV throughout. Ventral margin of valves straight on outer side and smoothly concave on inner side. Inner lamella broad, marginal pore canals short and occupying 20–50% of inner lamella width. Inner lamella of each valve with 65 marginal pore canals. Sensillae of outer lamella relatively sparse and emerging from small smoothed outgrouths ( Fig. 36I ). Microrelief of valve surface heterogenous: in central part it consists of shallow rounded pits with smooth margins ( Fig. 36H ), dorsal and ventral margins without pits. On ventral and dorsal margins microrelief in form of hemispheres ( Fig. 36A–36D ), on dorsal side hemispheres are smaller ( Fig. 36G ). Site of greatest width (both ventrally and dorsally) in center of L of carapace.

A1 ( Fig. 37B ) 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 three setae each. Seventh segment with five setae, one of them very small. Eighth segment with three setae and aesthetasc (ya).

A2 ( Fig. 38A, 38C, 38D ) five-segmented. Coxal segment with three setae, one of them inserted on this segment, two located between coxal and basal segments. One of them pappose. Basal segment with one ventro-distal seta. Exopod with three setae (one of them plumose distally to base). Endopod three-segmented. First endopodal segment with posteromedial club-shaped aesthetasc (Y) and two posterodistal setae. Second endopodal segment with one ventromedial seta, small dorsal-medial aesthetasc (y1), four t-setae (t1–t4) of different lengths, three z-setae (z1 short, z2 and z3 of similar length), three G-claws (G2 three times shorter than G1 and G3), and small distal aesthetasc (y2). Terminal segment with two G-claws (GM and Gm; GM longer than Gm), two setae, one of them basally fused with stick-shaped aesthetasc (y3).

Md ( Fig. 37A ). 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 (short and thin), and proximal seta. Second segment with six posterior setae (β-seta very small), two anterior setae, and two rows of pseudochaetae. Third segment with four posterodistal setae (γ-seta long and plumose), three anterior setae, and rows of pseudochaetae. Distal segment with two claws, three setae, and group of small pseudochaetae.

Mxl. Protopod without setae. First endite with 14 setae, two at base of endite, 12 at apex. Second endite with nine apical setae. Third endite with eight setae and two claws. Palp two-segmented, first segment with three plumose setae and one finely plumose seta. Distal segment with two claws and seta apically and three setae medially (two plumose and one smooth). Branchial plate with 23 setae and large number of separate groups of long pseudochaetae over entire surface of plate and long row of pseudochaetae.

L5 ( Fig. 39E, 39F ). 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 pseudochaetae. Branchial plate in form of two setae of different lengths.

L6 ( Fig. 39A, 39B ) five-segmented. First through third segments with one distal seta (d1, e, f) each and rows of small pseudochaetae. Fourth segment with two distal g-setae of different lengths and rows of small pseudochaetae. Fifth segment with long claw (h2) and two small setae (h1 and h3) of different lengths.

L7 ( Fig. 39C, 39D ) five-segmented. First segment with anterior d1-seta, posterior dp-seta; d2 seta absent. Second segment with rows of pseudochaetae. Third segment without pseudochaetae. Fourth segment with posterodistal g-seta and rows of pseudochaetae. Fifth segment with three serrate setae (h1–h3).

UR ( Fig. 39I ) symmetrical, with smoothly curved main axis. Each ramus with one posterior seta distal to midramus, one short anterodistal seta, and two thin distal claws of nearly equal length.

Male. Carapace ( Figs. 33E–33H ; 35A–35F ; 40F ) trapezoidal, slightly longer and lower than in female; L = 1920–2000 µm (average 1960 µm, n = 6), greatest H = 1140–1170 µm (average 1160 µm, n = 6) located on border of anterior 1/4 of L. Ventral margin of each valve with small conical projection ( Fig. 36E, 36F ), main axis of projections slightly directed posteriorly and towards the opposite valve. Shape and size of projections on RV and LV almost identical (projection on RV slightly narrower; Fig. 36E ), length 85–115 µm, width of bases 115– 150 µm. Microrelief as in female, but hemispheres on ventral side are smoothed near conical projections. Other morphological features of carapace structure, A1, A2 (protopod, exopod, first endopodal segment), Md, Mxl, L5 protopod, L6, L7 as in female.

A2 ( Fig. 38B, 38E, 38F ). Second endopodal segment with one anteromedial seta, small dorso-medial aesthetasc (y1), two t-setae (t1–t2) of similar length, three z-setae (z1 seta short, z3 seta long, and z2 modified into long serrated claw), three G-claws (G3 thin, 2 times shorter than G1, and almost 3 times shorter than G1), and distal aesthetasc (y2). Terminal segment with two G-claws (GM and Gm; Gm longer than GM) and two setae, one of them basally fused with aesthetasc (y3).

Prehensile palps of L5 ( Fig. 39G, 39H ) asymmetrical, finger-shaped, thickened. Main axis of palps smoothly curved distally to the site of insertion of two setae; setae on both palps short and thick. Distal tip of both palps with thick seta.

Hemipenis ( Fig. 41A ) large, irregularly rounded-rectangular, 715 µm long and 340 µm wide (including lobes); lobes ovoid, strongly protruding.

Zenker organ ( Fig. 42F ) 435 µm long, with 5+2 rings of spines 190 µm in diameter, diameter of central tube 75 µm, vesicle large, 145 µm in diameter.

UR ( Fig. 39J ) as in female, but main axis straighter.

Comparisons. The species is clearly distinguished from other Baikalian representatives of the genus by a large size, shell shape and conical ventral projections on the male valves. The structure of the A1 and A2 of both sexes and the male L5 prehensile palps, as well as the reproductive system (large hemipenes and Zenker organs with seven rosettes), allow this species to be distinguished from others.

Notes. When describing the species, Prof. G.F. Mazepova did not designate a holotype, but only indicated paratypes ( Mazepova 2001: p. 535), which are not valid without designation of the holotype and should be considered as syntypes, which was undertaken in the present work.

Females and males in copula were found ( Fig. 43E ).

Geographic distribution. Endemic to Lake Baikal, found in Aya Bay (depth 50 m); at capes Yador, Onguren and Koltygey; opposite Izhimey Сape (Olkhon Island); at the eastern coast of the lake (exact location not indicated) found at a depth of 300 m. Lives on silted sand ( Mazepova 1990: p. 254).

Figures

FIGURE 33. Pseudocandona olchonica Mazepova, 1990, 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—paralectotype No. 23; E–H—paralectotype No. 24. Scale 1000 µm.

FIGURE 34. Pseudocandona olchonica 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. 15; B—paralectotype No. 16; C—paralectotype No. 18; D—paralectotype No. 17; E—paralectotype No. 23; F—specimen No. 1. Scale 500 µm.

FIGURE 35. Pseudocandona olchonica 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—specimen No. 7; B—specimen No. 8; C—specimen No. 3; D—paralectotype No. 22; E—paralectotype No. 24; F—specimen No. 6. Scale 500 µm.

FIGURE 36. Pseudocandona olchonica Mazepova, 1990, SEM photographs of some elements of carapaces of females (A–D, G–I) and males (E, F): A—posterior part of carapace, laterally; B—microrelief near ventral margin, laterally; C—anterior part of carapace, laterally; D—posterior margin of carapace, ventrally; E—projections, ventrally; F—LV projection, laterally, inner side; G—central part of dorsal surface; H—microrelief in center of RV; I—sensilla. A–C, H, I—paralectotype No. 15; D—paralectotype 17; E—specimen No. 3; F—paralectotype No. 24; G—paralectotype No. 17. Scale, µm: A, C–E—200; B, F–H—100; I—10.

FIGURE 37. Pseudocandona olchonica Mazepova, 1990, drawings of female limbs: A—palp of Md without branchial plate; B—A1. A, B—paralectotype No. 23 Scale, µm: A—100; B—200.

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 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 40. Pseudocandona alta Bronstein, 1947 (A), Pseudocandona werestschagini (Bronstein, 1930) Bronstein 1947 (B), Pseudocandona grygieri Alekseeva & Krivorotkin sp. nov. (C), Pseudocandona renalis Mazepova, 1982 (E), Pseudocandona glauci Mazepova, 1990 (D) and Pseudocandona olchonica Mazepova, 1990 (F), 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 41. Pseudocandona alta Bronstein, 1947 (D), Pseudocandona werestschagini (Bronstein, 1930) Bronstein 1947 (B), Pseudocandona grygieri Alekseeva & Krivorotkin sp. nov. (C), Pseudocandona renalis Mazepova, 1982 (E), Pseudocandona glauci Mazepova, 1990 (F) and Pseudocandona olchonica Mazepova, 1990 (A), microphotographs of hemipenes.A—specimen No. 6; B—specimen No. 38; C—paratype No. 75; D—specimen No. 32; E—paralectotype No. 27; F—paralectotype No. 22. Scale 100 µm.

FIGURE 42. Pseudocandona alta Bronstein, 1947 (A), Pseudocandona werestschagini (Bronstein, 1930) Bronstein 1947 (B), Pseudocandona grygieri Alekseeva & Krivorotkin sp. nov. (C), Pseudocandona renalis Mazepova, 1982 (E), Pseudocandona glauci Mazepova, 1990 (D) and Pseudocandona olchonica Mazepova, 1990 (F), microphotographs of Zenker organs. A— specimen No. 32; B—specimen No. 39; C—paratype No. 75; D—paralectotype No. 22; E—paralectotype No. 27; F—specimen No. 6. 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.