Pseudocandona werestschagini (Bronstein, 1930) Bronstein 1947

Figs. 8–14; 40B; 41B; 42B

Type locality. Lake Baikal, between Peschanaya and Sennaya bays (approximate coordinates: 52°16′19 N, 105°43′15 E).

Type material. Neotype No. O10 (female): dwm No. O1-200869.

Additional material. Specimen No. 1 (male): dwm No. O1-200869. Specimens Nos. 2–13 (12 females): dwm No. O2-200869. Specimens Nos. 14–23 (10 males): dwm No. O3-200869. Specimens Nos. 24–35 (4 females, 8 males): swm No. 38. Specimen No. 36 (female): swm No. 38 (valves) and wm No. O4-200869 (limbs). Specimen No. 37 (female): swm No. 38 (valves) and wm No. O5-200869 (limbs). Specimen No. 38 (male): swm No. 38 (valves) and wm No. O6-200869 (limbs). Specimen No. 39 (male): swm No. 38 (valves) and wm No. O7-200869 (limbs).

All specimens were collected in Lake Baikal, southern basin, between Peschanaya and Sennaya bays, August 20, 1969, depth 11 m, stones with sponges and coarse sand, sample No. 209 from the collection of G.F. Mazepova.

Description. Female. Carapace (Figs. 8A–8D; 9A–9F; 40B) laterally rectangular-trapezoidal; L = 1090–1145 µm (average 1110 µm, n = 10), greatest H = 675–730 µm (average 710 µm, n = 10). Site of greatest H poorly defined and located in posterior 1/4 of L. Valves asymmetrical: RV trapezoidal and LV rectangular-trapezoidal. Dorsal margin of carapace straight. Anterior margin of valves widely rounded near ventral margin; posterior margin rounded more narrowly. Ventral margin on RV equally concave on outer and inner sides, and on LV almost straight on outer side, and concave on inner side. LV slightly overlaps RV throughout. Inner lamella relatively broad; marginal pore canals occupy 80–100% of inner lamella width. Inner lamella of each valve with 50–60 marginal pore canals. Most often, canal reaches margin of inner lamella and ends in sensilla; rarely, canals may not reach margin of inner lamella and open earlier. Sensillae of outer lamella relatively sparse and emerge from small outgrowths (Fig. 11C). Outer lamella of each valve with about 65 canals. Microrelief pitted (Fig. 11A–11C), almost homogenous on most valves, consisting of reticule of ribs and small rounded pits; pits gradually pass into reticule of ribs. Size of pits gradually decreases from carapace center to margins of valves, and on dorsal and ventral margin of valves, pits almost smooth out. Pitted microrelief visible on inner side of valves. Site of greatest width (both on ventral and dorsal sides) weakly expressed and located in central part of carapace.

A1 (Fig. 12E) seven-segmented. First segment with one finely plumose seta. Second segment with three finely plumose setae, two of nearly equal length, one shorter. Third segment with one finely plumose seta. Fourth segment with two distal setae and one medial seta. Fifth segment with two claws of unequal length and one seta. Sixth segment with three claws of unequal length and two setae (one very small). Seventh segment with two claws of unequal length, one seta and a small stick-shaped aesthetasc (ya).

A2 (Fig. 12A, 12B) 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 which short and smooth, one of medium length and smooth, and one long (large plumose in medial part). Endopod three-segmented. First endopodal segment with posteromedial club-shaped aesthetasc (Y), two posterodistal setae of almost equal length, and rows of pseudochaetae. Second endopodal segment with one ventromedial seta, small dorsal-medial aesthetasc (y1), two t-setae (t1, t2) of nearly equal length, three z-setae (z1 half as long as z2 and z3), three G-claws (G2 3 times shorter than G1 and G3), and small distal aesthetasc (y2); segment with rows of pseudochaetae. Terminal segment with two G-claws (GM and Gm; GM longer than Gm), two setae, one of which basally fused with stick-shaped aesthetasc (y3), and several rows of pseudochaetae.

Md (Fig. 13A). 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 one. Second segment with six posterior setae (β-seta very small) and two anterior setae. Third segment with four posterodistal setae (γ-seta long and plumose) and three anterior setae. Distal segment with two claws, three setae, and group of pseudochaetae.

Mxl (Fig. 13B–13F). Protopod without setae. First endite with 15 setae, two of which inserted at base of endite, 13 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 smooth seta. Distal segment with two claws and one seta in apical part and three setae in medial part. Branchial plate with 23 setae.

L5. Protopod with three setae (a, b, d). Endite with 14 setae, arranged in two groups of four and ten setae, and several rows of long pseudochaetae. Palp with three setae and rows of short pseudochaetae. Branchial plate in form of two setae of different lengths.

L6 (Fig.14C) five-segmented.First to third segments with one 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 small setae (h1 and h3) of different lengths.

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

UR (Fig. 14E) 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 nearly equal length.

Male. Carapace (Figs. 8E–8H; 10A–10H; 40B) laterally rectangular-trapezoidal, slightly shorter and lower than in female; L = 960–1065 µm (average 1020 µm, n = 10), greatest H = 625–650 µm (average 630 µm, n = 10). Site of greatest H slightly more pronounced and located in posterior 1/4 of L. Inner lamella relatively broad; marginal pore canals occupy 60–80% of width of inner lamella. Inner lamella of each valve of same individual with 45–60 marginal pore canals. Other morphological features of carapace structure, A1, A2 (protopod, exopod and first endopodal segment, except for distal setae, which are of different lengths in male), Md, Mxl, L5 protopod, L6, L7 as in female.

A2 (Fig. 12C, 12D). Second endopodal segment with one ventromedial seta, small dorsal-medial aesthetasc (y1), two t-setae (t1, t2, shorter than in female), three z-setae (z1 and z2 modified into long claws, z3-seta as long as z1 and z2), three G-claws (G2 longest, G1 slightly shorter, G2 2.5 the length of G3), small distal aesthetasc (y2) and rows of pseudochaetae. Terminal segment with two G-claws (short GM and long Gm) and two setae, one of them basally fused with stick-shaped aesthetasc (y3).

Prehensile palps of L5 (Fig. 14A, 14B) asymmetrical, stick-shaped, right one slightly stronger than left. Right palp smoothly curved in central part, and its thickness increases towards place of insertion of two medial setae (both in center of segment) and smoothly decreases distally. Left palp curved more sharply, its thickness smoothly decreases towards distal end. Medial setae of left palp inserted in different places: one in center of palp, second more proximally. Distal tip of both palps with thin seta.

Hemipenis (Figs. 11D; 41B) large, rectangular, 390 µm long and 165 µm wide; lobes oval, weakly protruding.

Zenker organ (Fig. 42B) 255 µm long, with 4+2 rings of spines 95 µm in diameter; central tube 40 µm in diameter; proximal vesicle large, 85 µm in diameter.

UR (Fig. 14D) as in female, but rami slightly thinner.

Comparisons. Due to the almost rectangular carapace, individuals of P. werestschagini are clearly distinguished from individuals of other Baikalian species of the genus, but in lateral view they remotely resemble individuals of Pseudocandona pseudosetosa Mazepova, 1990 .

Notes. As in the case of the previous species, type material was not isolated (Bronstein 1930), and syntypes (Mazepova 2001: pp. 532, 533) are incorrectly designated. The reasons are given in the Notes to the previous species.

Geographic distribution. Endemic to Lake Baikal, found in all three basins and in the Maloye More Strait at depths from 3 to 100 m (Mazepova 1990: pp. 224, 225). Lives on sand, stones and silty substrate.