Microlaimus sergeevae, Revkova, 2020

Revkova, Tatiana N., 2020, A new species of Microlaimus de Man 1880 (Nematoda: Microlaimidae) from the Black Sea, Zootaxa 4772 (1), pp. 183-188 : 184-187

Microlaimus sergeevae sp. n.

( Figs 1 , 2 ; Table 1)

Material studied: six males and three females. Glycerin-gelatin slides. Holotype male on slide # FlN/BS -24. Para- type: males # FlN/BS -25 to # FlN/BS -29 and females # FlN/BS -30 to # FlN/BS -32.

Type locality: Black Sea, Crimea, Sevastopol, Bay Kruglaya, 8.5 m, silty sand with detritus; water salinity 17.6 ‰. Geographical coordinates 44°36’11.7”N 33°26’33.4”E.

Etymology: The species name is in honor of Prof. Nelli G. Sergeeva.

Description: Male. Body long and slender. Cuticle with distinct annuli; begin immediately posterior to cephalic setae (ring width 1 μm) to near tail tip; in the middle of the body 2 μm. Four submedian rows of round pores 1 μm in diameter, situated along whole body. Cervical setae ( Fig. 2D ), 3.7 μm long. Six inner labial papillae and six outer labial papillae in two separate circles; four cephalic setae 7.5–9 μm long. Cryptocircular amphideal fovea 53.3–68.1 % of corresponding body diameter with interruption in the posterior part. Distance from cephalic end to anterior border of amphidial fovea 12–14 μm. Buccal cavity weakly sclerotized with small dorsal and two subven- tral teeth. Pharynx narrow, cylindrical and muscular along its entire length; having a well-developed terminal oval bulb 19–24 μm in width. Nerve ring is located at a distance of 43.5–56.4 %. Secretory- excretory system present; renette cell situated posterior to cardia, on the ventral side and excretory pore not observed. Cardia is not surrounded by intestinal tissue. Sperm cells elongated, maximum size 8 × 22 μm.

Reproductive system diorchic, testes opposed and outstretched. Anterior testis situated to left of intestine, pos- terior testis to right of intestine. Spicules curved, 1.1–1.4 of anal body diam. Gubernaculum surrounding distal end of spicules, with dorsally directed apophyses. A row of 8 pre-cloacal supplements in the form of thin channels in the center of each papilla is located in front of the anus. Tail conical (3.2–4.3 of anal body diam.), slightly swollen at the end. Precloacal setae absent. On the tail there is a row of 8 subventral caudal setae (4 µm long), visible in a light microscope.

Female. Similar to males in most respects. Reproductive system didelphic, with opposed and outstretched geni- tal branches both situated ventrally relative to intestine. Anterior genital branch 210–255 μm long, posterior genital branch 255–340 μm long. Vulva situated slightly posterior to mid-body 53.1–55.9 %. Vagina with thick walls is perpendicular to the longitudinal body axis. Diameter of the large oocyte 13 × 41 μm in female1. Vulval glands are present, two different types anterior and posterior to the vagina.

Diagnosis. M. sergeevae sp. n. from the Black Sea is characterized by the 1301–1728 μm long body; cuticle with distinct annuli; spicules 34–37 μm long, curved; gubernacular apophyses 20–25 μm long, surrounding distal end of spicules; criptocyrcular amphidial fovea 7–8 μm in diameter; cervical setae present; four submedian rows of pores spreading along the whole body length, and eight precloacal supplements in males.

Different diagnosis: M. sergeevae sp. n. mostly resembles M. gerlachi Wieser 1954 , M. paraborealis Allgen 1940a and M. kaurii, Wieser 1954 , but differs from them in the size of cephalic setae, shape of the gubernacular apophyses, presence of cervical setae and four submedian rows of pores spreading along the whole body length. M. sergeevae sp. n. differ from M. gerlachi by the size of the body 1301–1728 μm vs. 1630–2470 μm, shorter spicules 34–37 μm (1.1–1.4 of anal body diam.) vs. 52 μm (1.1 of anal body diam.) and gubernacular apophyses 20–25 μm vs. 36 μm, smaller amphidial fovea 7–8 μm (53.3–68.1 % of corresponding body diameter) vs. 9–10 μm (44–50 % of corresponding body diameter) and presence eight precloacal supplements. Meanwhile, Wieser (1954) also mentioned some slight elevations of pre-cloacal supplements in the original description of M. gerlachi . The new species differs from M. kaurii by having a larger body (1301–1728 μm vs. 700–960 μm), large values of c (12.1–16.5 vs. 8.6–11.1) and b (10.9–13.1 vs. 6.5–8.3); larger spicules 34–37 μm (1.1–1.4 of anal body diam.) vs. 26–31 μm (1.3 of anal body diam.), and presence of eight precloacal supplements. The Black Sea specimens differ from M. paraborealis by a large value of c (12.1–17.7 vs. 9–10.3).

TABLE 1. Morphometrics of Microlaimus sergeevae sp. n. (All measurements are given in μm unless otherwise stated, except for the ratios a, b, c, cʹ)

Figures

FIGURE 1. Microlaimus sergeevae sp. n. Male: A: entire male; B: head; C: anterior body region; D: posterior body region; Female 1. E: head; F: entire female 1; G: anterior body region. Scale bar: A, F = 100 μm; C, D, G = 50 μm; B, E = 10 μm.

FIGURE 2. Microlaimus sergeevae sp. n. A: entire male; B: entire female 1; C: head region of male; D: amphid of male; E: lateral row of pores; F: tail region of male; G: spicula and precloacal supplements. Scale bar: A, B = 100 μm; E, F = 50 μm; C, D, G = 20 μm.