Pseudocandona grygieri Alekseeva & Krivorotkin sp. nov.

Figs. 15–21; 40C; 41C; 42C; 43A, 43B

Type locality. Lake Baikal, coastal zone of Senogda Bay (approximate coordinates: 55°34′15 N, 109°12′48 E).

Type material. Holotype No. O10 (male) and allotype No. O10.1 (female): dwm No. O10-260972. Paratypes Nos. 1–24 (24 females): dwm No. O11-260972. Paratypes Nos. 25–62 (38 males): dwm No. O12-260972. Paratypes Nos. 63–71 (4 females, 5 males): swm No. 42. Paratype No. 72 (female): swm No. 42 (valves) and wm No. O13- 260972 (limbs). Paratype No. 73 (female): swm No. 42 (valves) and wm No. O14-260972 (limbs). Paratype No. 74 (female): swm No. 42 (valves) and wm No. O15-260972 (limbs). Paratype No. 75 (male): swm No. 42 (valves) and wm No. O16-260972 (limbs). Paratype No. 76 (male): swm No. 42 (valves) and wm No. O17-260972 (limbs). Paratype No. 77 (male): swm No. 42 (valves) and wm No. O18-260972 (limbs). Paratype No. 78 (male): swm No. 42 (valves) and wm No. O19-260972 (limbs). Paratypes Nos. 79, 80 (male and female in copula): swm No. 42.

All specimens were collected in Lake Baikal, northern basin, in the coastal zone of Senogda Bay, September 26, 1972, depth 10 m, slightly silted sand, sample No. 434 from the collection of G.F. Mazepova.

Etymology. The species is named in honor of Mark J. Grygier (National Museum of Marine Biology & Aquarium, Taiwan), specialist in taxonomy, nomenclature, systematics, biology of crustaceans (Facetotecta, Ascothoracida, Monstrilloida) and previously a member of the Commission of the International Code of Zoological Nomenclature.

Description. Female. Carapace (Figs. 15A–15D; 16A–16H; 40C) laterally rectangular-trapezoidal; L = 1090– 1145 µm (average 1125 µm, n = 10), greatest H = 755–805 µm (average 780 µm, n = 10). Site of greatest H poorly expressed 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 and ventral margins form acute angle (about 75°). Ventral margin on RV equally concave on outer and inner sides; on LV it is almost straight on outer side, and concave on inner side. LV slightly overlaps RV throughout. Inner lamella relatively broad; marginal pore canals occupy 70–100% of width of inner lamella. Inner lamella of each valve with 55–60 marginal pore canals. Most often, canal reaches the margin of inner lamella and ends in sensilla; rarely, canals may not reach the margin of inner lamella and open earlier. Sensillae of outer lamella relatively sparse and emerge from small outgrowths (Fig. 18C, 18E). Microrelief pitted, almost homogenous on most of valves (Fig. 18A). Pitted microrelief becomes more complex at posterior part of carapace: ribs appear in each pit, dividing the pit into smaller pits (in females, this microrelief less pronounced than in males in Fig. 18B). Microrelief smoothed out at dorsal margin, valves almost smooth. Pitted microrelief visible on inner side of valves. Site of greatest width (both on ventral and dorsal sides) almost not expressed and located in central part of carapace. Anterior end of carapace in dorsal and ventral views is less sharp compared to previous species.

A1 (Fig. 19A) seven-segmented. First segment with one finely plumed seta. Second segment with three setae, two of them almost equal length, one shorter and finely plumed. Third segment with one seta. Fourth segment with two distal setae and one medial seta. Very small area with residual division of segments in center of fourth segment near medial seta. Fifth segment with three setae of different lengths. Sixth segment with two claws of different lengths and three setae (one of them very small). Seventh segment with two claws of different lengths, one seta and small stick-shaped aesthetasc (ya).

A2 (Fig. 19B, 19C) five-segmented. Coxal segment with three setae, one of them inserted to this segment, two located between coxal and basal segments. One of them pappose. Basal segment with one ventro-distal seta. Exopod with three setae of different lengths, of which one short and smooth, one of medium length and finely plumed and one long and coarsely plumed (smooth in proximal length third). Endopod three-segmented. First endopodal segment with posteromedial club-shaped aesthetasc (Y), two posterodistal setae of equal length, and row of pseudochaetae. Second endopodal segment with one ventromedial seta, small dorsal-medial aesthetasc (y1), two t-setae (t1, t2) of equal length, three z-setae (z1 four times shorter than z2 and three times shorter than z3), three G-claws (G2 three times shorter than G1 and G3), small distal aesthetasc (y2) and rows of pseudochaetae. Last segment with two Gclaws (GM and Gm; GM longer than Gm), two setae, one of them basally fused with stick-shaped aesthetasc (y3) and row of pseudochaetae.

Md (Fig. 20A). 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 six posterior setae (β-seta very small) and two anterior setae. Third segment with four posterodistal setae (γ-seta long and plumose), three anterior setae and group of pseudochaetae. Distal segment with two claws, three setae and group of pseudochaetae.

Mxl (Fig. 20B–20F). 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 smooth seta. Distal segment with two claws and one seta distally and three setae medially (two plumose and one smooth). Branchial plate with 23 setae and row of pseudochaetae.

L5 (Fig. 21A). Protopod with three setae (a, b, d). Endite with 14 setae, arranged in two groups of four and ten setae and two rows of pseudochaetae. Palp with three setae and numerous rows of small pseudochaetae. Branchial plate in form of two setae of different lengths.

L6 (Fig. 21D) five-segmented. First through 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 (Fig. 21E) 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. 21F) 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. 15E–15H; 17A–17H; 40C) laterally rounded-trapezoidal, slightly longer and lower than in female; L = 1120–1195 µm (avearage 1150 µm, n = 10), greatest H = 730–780 µm (average 760 µm, n = 10). Posterior margin of carapace widely rounded, compared to that of female. Inner lamella narrower than in female; marginal pore canals occupy 40–100% of width of inner lamella. Microrelief in form of large pits divided into smaller pits (Fig. 18B) more pronounced than in female. Other morphological features of carapace structure, A1, A2 (protopod, exopod and first endopodal segments with except for distal setae, which of different lengths in male; Fig. 19D), Md, Mxl, L5 protopod, L6, L7 as in female.

A2 (Fig. 19D, 19E). Second endopodal segment with one ventromedial seta, small dorsal-medial aesthetasc (y1), one t-seta (t1), three z-setae (z1 and z2 modified into long claws, z3-seta two times shorter than z1 and z2), three G-claws (G2 longest; G1 1.5 times shorter than G2; G3 2.5 times shorter than G2), small distal aesthetasc (y2), and rows of pseudochaetae. Last 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. 21B, 21C) asymmetrical, main axis smoothly curved distally to insertion of two setae. Right palp slightly thicker than left. Medial setae of right palp attached next to each other. Medial setae of left palp attached in different places: one in center of palp, and other distally. Distal tip of both palps with very small seta.

Hemipenis (Figs. 18F; 41C) large, oval-rectangular, 510 µm long and 235 µm wide (including lobes); lobes irregularly ovoid, strongly protruding.

Zenker organ (Fig. 42C) 305 µm long, with 4+2 rings of spines 150 µm in diameter, central tube 45 µm in diameter, small vesicle 50 µm in diameter.

UR (Fig. 21G) as in female, but rami slightly thinner.

Comparisons. Female valves of the new species are generally similar to those of P. werestschagini females (Fig. 10E, 10F), but differ in an acute posterior end (Fig. 16E, 16F). Valve outlines of the males studied are significantly distinct (Figs. 10A, 10B; 17A, 17B). In dorsal and ventral views, the anterior and posterior ends of the carapaces of P. werestschagini males and females are thinner and more pointed (Figs. 9C, 9D; 10C, 10D, 10G, 10H) compared to the new species (Figs. 16C, 16D, 16G, 16H; 17C, 17D, 17G, 17H). In general, the shells of male and female specimens of the new species are noticeably wider. The microrelief of P. werestschagini specimens is pitted, almost homogeneous; individuals of P. grygieri sp. nov. have pits divided into smaller pits in the posterior part of the valves (Fig. 18B). Comparisons of the limbs of the species show an array of differences (prehensile palps of the male L5, size of the medial setae on the fourth A1 segment and others). The male hemipenes also differ (Figs. 11D; 18F; 41B, 41C). The Zenker organs of P. werestschagini males have a much larger vesicle than that of the new species (Fig. 42B, 42C).

Notes. Females and males in copula were found (Figs. 18D; 43A, 43B).

Geographic distribution. Endemic to Lake Baikal, found in Senogda Bay (depth 10 m). Lives on slightly silted sand.