Pseudocandona alta Bronstein, 1947

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 : 4-13

Pseudocandona alta Bronstein, 1947

Figs. 1–7 ; 40A ; 41D ; 42A

Type locality. Lake Baikal , Maloye More Strait, coastal zone opposite Arul Cape (approximate coordinates: 53°28′27 N, 107°32′54 E).

Type material. Neotype No. O9 ( female): dwm No. O1-120868 .

Additional material. Specimen No. 1 ( male): dwm No. O1-120868 . Specimens Nos. 2–9 ( 8 females): dwm No. O2-120868 . Specimens Nos. 10–18 ( 9 males): dwm No. O3-120868 . Specimens Nos. 19–29 ( 4 females, 7 males): swm No. 39 . Specimen No. 30 ( female): swm No. 39 (valves) and wm No. O4-120868 (limbs). Specimen No. 31 ( female): swm No. 39 (valves) and wm No. O5-120868 (limbs). Specimen No. 32 ( male): wm No. O6-120868 (limbs). Specimen No. 33 ( male): wm No. O7-120868 (limbs). Specimen No. 34 ( male): wm No. O8-120868 (limbs). Specimens Nos. 35–40 ( 6 juvenile stages): swm No. 40 .

All specimens were collected in Lake Baikal, in Maloye More Strait, coastal zone opposite Arul Cape, on August 12, 1968, at a depth of 5 m, in a habitat of stones with sponges and draparnaldia (most likely G.F. Mazepova meant representatives of the genus Draparnaldioides , endemic green macroalgae to Baikal), sample No. 170 from the collection of G.F. Mazepova.

Description. Female. Carapace ( Figs. 1A–1D ; 2A–2F ; 40A ) laterally trapezoidal; L = 885–940 µm (average 905 µm, n = 9), greatest H = 520–600 µm (average 560 µm, n = 9) located on border of anterior 1/ 3 L. Dorsal margin of carapace straight, with small keel on LV, crescent-shaped in dorsal view ( Fig. 2D ). Anterior margin of valves broadly rounded near ventral margin; posterior margin narrowly rounded. Central part of ventral margin of both valves almost equally concave on outer and inner sides. LV noticeably overlaps RV throughout. Inner lamella relatively broad; marginal pore canals occupy 30–50% of width of inner lamella. Inner lamella of RV with more marginal pore canals (about 90) than inner lamella of LV (about 65). Difference in number of marginal pore canals occurs because area of inner lamella and marginal pore canals captures the posterior part of dorsal margin. Most often, canals reach margin of lamella and end with sensilla, rarely canals may not reach the margin of inner lamella and open before that. Sensillae of outer lamella relatively sparse and emerge from small outgrowths ( Fig. 4B ). Outer lamella of each valve with 115–125 pore canals. Microrelief cellular (depressions and reticule of ribs as in Fig. 4A, 4B ), almost homogeneous on most of valves. Size of cells gradually decreases from center of valves to their margin; cells become very small and shallow and almost disappear only on dorsal and ventral margins. Cellular microrelief slightly visible on inner side of valves ( Fig. 2E, 2F ). Site of greatest width (both on ventral and dorsal sides) slightly behind central part of carapace.

A1 ( Fig. 5A ) seven-segmented. First segment with one plumose seta. Second segment with three setae (two of them almost same length, third is shorter) and row of pseudochaetae. Third segment with one seta. Fourth segment with two short setae. Fifth segment with two long setae. Sixth segment with five setae of different lengths. Seventh segment with three setae of different lengths and stick-shaped aesthetasc (ya).

A2 ( Fig. 5B, 5C ) five-segmented. Coxal segment with three setae, one inserted on this segment and two setae located between coxal and basal segments. One of them pappose. Basal segment with one ventro-distal seta and row of pseudochaetae. Exopod with three setae, one short and smooth, one short plumose and one long plumose (smooth in proximal third of length). Endopod three-segmented. First endopodal segment with posteromedial club-shaped aesthetasc (Y), two posteromedial setae of different lengths, and row of pseudochaetae. Second endopodal segment with one ventromedial seta, small dorsal-medial aesthetasc (y1), three t-setae (t1–t3) of approximately same length, three z-setae (z1–z3), three G-claws (G1–G3) of same length and small distal aesthetasc (y2). Distal segment with two G-claws (GM and Gm; GM slightly longer than Gm) and two setae, one of which basally fused with stick-shaped aesthetasc (y3).

Md ( Fig. 6F ). Coxa with one subapical seta and several setae between teeth of endite and on apical inner corner. Branchial plate with seven plumed setae and one smooth seta. Palp four-segmented. First segment with four setae: S1 (long, plumed), S2 (short, pappose), α (thin and short) and proximal seta. Second segment with six posterior setae (β-seta very small), two anterior setae and row of pseudochaetae. Third segment with four posterior-distal setae (γ-seta large and plumed), three anterior setae and two rows of pseudochaetae. Distal segment with two claws, two setae (one short and other long) and group of pseudochaetae.

Mxl ( Fig. 6A–6E ). Protopod without setae. First endite with 14 setae, two of them at base of endite, 12 at apex. Second endite with eight setae at apex. Third endite with nine setae and two claws. Palp two-segmented; first segment with four setae and row of pseudochaetae, distal segment with two claws and one seta apically and three setae medially. Branchial plate with 24 setae and long row of pseudochaetae.

L5 ( Fig. 7C ). Protopod with four setae (a, a’, b, d). Endite with 14 setae arranged in two groups of four and ten setae; two rows of pseudochaetae on endite. Palp with three setae and rows of small pseudochaetae. Branchial plate with two setae of different lengths.

L6 ( Fig. 7A ) five-segmented.First to third segments with one distal seta (d1, e, f) each and rows of pseudochaetae. Fourth segment with two g-setae and rows of pseudochaetae. Fifth segment with long claw (h2) and two small setae (h1 and h3) of different lengths.

L7 ( Fig. 7B ) four-segmented. First segment with anterior d1-seta and posterior dp-seta; d2-seta absent. Second segment with rows of pseudochaetae. Third segment with one posterior-distal g-seta and rows of pseudochaetae. Fourth segment with three serrate setae (h1–h3), all of different lengths.

UR ( Fig. 7G ) symmetrical, with slightly curved main axis. Each ramus with one posterior seta distal to middle of ramus, one short anterodistal seta and two distal claws of different lengths.

Male. Carapace ( Figs. 1E–1H ; 3A–3H ; 40A ) laterally trapezoidal, slightly longer and higher than in female; L = 885–960 µm (average 920 µm, n = 10), greatest H = 570–620 µm (average 600 µm, n = 10) located in posterior 1/3 of L. Site of greatest H more pronounced than in female. Posterior margin of carapace slightly rounder than in female. Inner lamella relatively broad; marginal pore canals occupy 30–60% of width of inner lamella. Other morphological features of carapace structure, A1, A2 (protopod, exopod and first endopodal segment), Md, Mxl, L5 protopod, L6, L7 as in female.

A2 ( Fig. 5D, 5E ). Second endopodal segment with one ventromedial seta, small dorsal-medial aesthetasc (y1), three t-setae (long t1 and small t2 and t3), three z-setae (z1 and z2 modified into long claws, and z3 simple seta), three G-claws (G1 and G3 2.5 times shorter than G2) and small distal aesthetasc (y2). Last segment with two Gclaws (long Gm, and shorter GM basally fused with segment) and two setae, one of them basally fused with stick-shaped aesthetasc (y3).

Prehensile palps of L5 ( Figs. 4D ; 7D, 7E ) slightly asymmetrical, thin and stick-shaped, main axis smoothly curved distal to insertion of one of setae. Right palp slightly thicker than left one. Medial setae on both palps different in size and structure: one long and inserted in center of palp, second short and located between insertion of first seta and distal tip of palp. Distal tip of both palps with thin seta.

Hemipenis ( Figs. 4E ; 41D ) small, rectangular, 295 µm long including lobes and 140 µm wide; lobes oval, strongly protruding, especially outer one.

Zenker organ ( Fig. 4C ; 42A ) 350 µm long, with 4+2 rings of spines 170 µm in diameter, diameter of central tube 30 µm, which corresponds to diameter of small proximal vesicle.

UR ( Fig. 7F ) as in female, but main axis straighter.

Juvenile stages are almost identical to adults in carapace structure ( Fig. 2G–2I ).

Comparisons. Carapaces of P. alta individuals in lateral view are clearly distinguished from most Baikalian species of the genus. They are somewhat reminiscent of trapezoid shells of individuals of some species of the genus Baicalocandona Mazepova, 1976 , but differ in the presence of a continuous cellular microrelief and five-segmented A 2 in both sexes.

Notes. When describing the species, Z.S. Bronstein (1947) did not distinguish type specimens. In 2001, G.F. Mazepova designated syntypes ( Mazepova 2001: p. 534), which cannot be syntypes, since they were collected only in 1968, which is significantly later than the publication of the original description. The designation of syntypes does not correspond to the International Code of Zoological Nomenclature (1999). For this reason, we designate a neotype based on the material of G.F. Mazepova.

Geographic distribution. Endemic to Lake Baikal, found in all three basins and in the Maloye More Strait at depths of 1–25 m ( Mazepova 1990: pp. 237, 238). Inhabits stony and sandy substrates.

Figures

FIGURE 1. Pseudocandona alta Bronstein, 1947, 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. Here and for other figures, arrows point towards the anterior. A–D—specimen No. 30; E–H—specimen No. 27. Scale 400 µm.

FIGURE 2. Pseudocandona alta Bronstein, 1947, SEM photographs of carapaces (A–D, G–I) and valves (E, F) of females (A– F) and juvenile stages (G–I):A, B, G, H—laterally, outer side; C—ventrally; D, I—dorsally; E—LV laterally, inner side; F—RV laterally, inner side. A—specimen No. 20; B—specimen No. 19; C—specimen No. 22; D—specimen No. 21; E, F—specimen No. 30; G—specimen No. 38; H—specimen No. 37; I—specimen No. 39. Scale 500 µm.

FIGURE 3. Pseudocandona alta Bronstein, 1947, 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—specimen No. 24; B—specimen No. 23; C—specimen No. 26; D—specimen No. 25; E, F—specimen No. 27; G, H—specimen No. 29. Scale 500 µm.

FIGURE 4. Pseudocandona alta Bronstein, 1947, SEM photographs of some morphological characters of female (A, B) and male (C–E): A, B—microrelief and sensillae in center of LV, laterally, outer side; C—Zenker organ; D—left prehensile palp of L5; E—hemipenis. A, B—specimen No. 19; C–E—specimen No. 27. Scale, µm: A, C–E—100; B—20.

FIGURE 5. Pseudocandona alta Bronstein, 1947, drawings of limbs of female (A–C) and male (D, E): A—A1; B—A2 without distal segment; C, E—distal segments of A2; D—distal part of third and fourth segments of A2. A–C—specimen No. 30; D, E—specimen No. 32. Scale 100 µm.

FIGURE 6. Pseudocandona alta Bronstein, 1947, drawings of limbs of female (A–E) and male (F): A—branchial plate of Mxl; B—protopod and palp with fragment of branchial plate of Mxl; C—third endite of Mxl; D—second endite of Mxl; E—first endite of Mxl; F—Md. A–E—specimen No. 31; F—specimen No. 34. Scale 100 µm.

FIGURE 7. Pseudocandona alta Bronstein, 1947, drawings of limbs of female (A–C, G) and male (D–F): A—L6; B—L7; C—L5; D—right prehensile palp of L5; E—left prehensile palp of L5; F, G—UR.A–C—specimen No. 31; D–F—specimen No. 32; G—specimen No. 30. Scale 100 µm.

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.