Leptolaimus pellucidus ( Southern, 1914 ) Holovachov & Boström, 2013

Holovachov, Oleksandr & Boström, Sven, 2013, Swedish Plectida (Nematoda). Part 4. The genus Leptolaimus de Man, 1876, Zootaxa 3739 (1), pp. 1-99 : 35-38

Leptolaimus pellucidus ( Southern, 1914) comb. n.

( Figs 14–16 ; Table 10)

Material examined. 18 males and 29 females (slides # 130540–130546) deposited in the general invertebrate collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden .

Habitat and locality. Shells and sand from 15–22 m deep, Skagerrak off the west coast of Sweden (N 58° 12' 37'', E 11° 18' 53''), 09 August 2011, legit O. Holovachov (18 males and 29 females) .

Description. Adult. Body tapering anteriorly in pharyngeal region and posteriorly on tail; ventrally curved upon fixation, more strongly curved ventrad in posterior part in males. Maximum body diameter at vulva in female; male body more cylindrical. Cuticle annulated; annuli 3.1–3.9 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 1.5–2.0 µm wide at mid-body; originating at level of metacorpus (posterior to first body pore) and extending posteriorly to middle or posterior third of tail. Prominent body pores in sublateral position at both sides of lateral field present, arising from oval lateral epidermal gland cells; 7–11 pairs of body pores are present along pharyngeal region; numerous body pores scattered over rest of the body. Anteriormost body pore located at level of procorpus. One pair of dorsosublateral setae are located a short distance posterior to nerve ring, similar to Stephanolaimus elegans Ditlevsen, 1918 as described by Holovachov & Boström (2004). Labial region truncate, continuous with body contour, lips fused. Inner labial sensilla indistinct. Outer labial sensilla papilliform, located on the anterior surface of lips. Cephalic sensilla setiform, equal to 40–70% of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea round, located at level of anterior 1/3rd of stoma. Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretory-excretory system present; excretory pore located posterior to nerve ring, just in front of the basal bulb. Buccal cavity uniformly tubular: cheilostom and gymnostom short, undifferentiated; stegostom tubular, with uniformly thickened lumen. Pharynx muscular, cylindrical anteriorly, with distinct oval basal bulb; valvular apparatus absent. Anterior cylindrical part of pharynx subdivided by breaks in muscular pharyngeal tissue into cylindrical procorpus, cylindrical metacorpus and narrow isthmus. Pharyngeal glands and their orifices indistinct. Cardia conoid, its posterior part embedded in intestine. Tail similar in shape in both sexes (more curved ventrad in male), conoid, gradually narrowing distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. No additional setiform sensilla along the pharyngeal region. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with arcuate cylindrical calamus and ovoid manubrium. Gubernaculum plate-like, with paired dorsal apophyses. Accessory apparatus composed of one midventral precloacal setiform sensillum located on anterior cloacal lip, one midventral setiform sensilla located midway between cloaca and posteriormost supplement, 5–9 evenly spaced midventral tubular supplements extending for 291–405 µm from cloaca towards anterior end; 2–5 midventral tubular supplements along the pharyngeal region; alveolar supplements absent. Tubular supplements located along the pharyngeal region are hook-like in shape, tubular supplements located along the posterior body region are weakly sigmoid or weakly arcuate in shape, with anchor-like tips. Posteriormost tubular supplement 64–71 µm anterior to cloaca, anterior to spicules. Sublateral precloacal and caudal sensilla present: four (one ventrosublateral and one dorsosublateral pair) precloacal setae at level of spicules and 6–8 caudal setae arranged in 3–4 subventral pairs.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 200–314 µm long (equal to 11.1–19.4% of total body length), located on right-hand side of intestine (n=9) or left-hand side of intestine (n=2), posterior genital branch 214–329 µm long (equal to 11.9–20.0% of total body length), located on left-hand side of intestine (n=11). Oviduct a narrow tube. One offset, oval, sac-like spermatheca located on right side of anterior gonoduct and one on left side of posterior gonoduct. Spermathecae often filled with oval spermatozoa. Uterus a wide and long tube, often filled with spermatozoa as well. Vagina straight, 0.3–0.4 times vulval body diameters long; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae absent. Vulva midventral. Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Two to four tubular supplements present: one to three anterior located along the pharyngeal region, and one posterior located in front of anus, 9–13 µm anterior to anal opening. Rectum 1.0–1.5 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis (supplemented with literature data). Leptolaimus pellucidus is particularly characterised by the 1460–1935 µm long body; truncated labial region continuous with body contour; cephalic setae 3.5–8.0 µm long; amphid located 8.5–11.0 µm from anterior end; first body pore located 38.0–51.0 µm from anterior end; lateral field originating 71.5–92.0 µm from anterior end; female with 1–3 tubular supplements along pharyngeal region and one tubular supplement in front of anus, vagina without pars refringens, vulva midventral; male with 2–5 tubular supplements along pharyngeal region and 5–9 tubular supplements in front of cloaca, without alveolar supplements, tubular supplements hook-like or weakly arcuate in shape with anchor-like tips; spicules arcuate and 47.0–70.0 µm long.

Remarks. Current specimens agree well with the type specimens in general morphology, measurements, number, arrangement and shape of tubular supplements, presence of two midventral precloacal setiform sensilla in male, and shape of spicules and gubernaculum. The only difference is somewhat longer spicules in our specimens (55.0–68.0 µm vs. 47.0–52.0 µm in the original description). A single male specimen described by Gerlach (1953a) also agrees well with the current material in both morphology and morphometrics, with the exception of longer cephalic setae (8 µm vs. 3.5–5.0 µm in current specimens), and slightly longer spicules (70.0 µm vs. 55.0–68.0 µm in current specimens).

Figures

FIGURE 14. Leptolaimus pellucidus (Southern, 1914) comb. n., male (A–C) and female (D–F). A: Anterior end, surface view; B: Pharyngeal region, median section; C: Male posterior region; D: Female tail; E: Female reproductive system (anterior part); F: Anterior end with aberrant (asymmetrical) position of amphid. Scale bar: A–F = 20 µm.

FIGURE 15. Leptolaimus pellucidus (Southern, 1914) comb. n., male (A, D–E, G–J) and female (B–C, F, K). A: Anterior end, right lateral view; B: Tubular supplement located along the pharyngeal region; C: Tubular supplement located in front of anus; D: Anterior end, semi en–face view; E: Male caudal region; F: Female vulval region; G: Second most posterior supplement in male; H: Most posterior supplement in male; I: Male anterior body end; J: Male posterior body end; K: Female tail. Scale bars: A–B, E–F, K = 10 µm, C–D, G–H = 5 µm, I–J = 50 µm.

FIGURE 16. Leptolaimus pellucidus (Southern, 1914) comb. n. A: Entire female; B: Entire male. Scale bar: A–B = 50 µm.