Leptolaimus venustus Lorenzen, 1972

Holovachov, Oleksandr & Boström, Sven, 2013, Swedish Plectida (Nematoda). Part 4. The genus Leptolaimus de Man, 1876, Zootaxa 3739 (1), pp. 1-99 : 39-43

Leptolaimus venustus Lorenzen, 1972

( Figs 17 , 18 E–F ; Table 11)

Material examined. 29 males and 39 females (slides # 130457–130560) deposited in the general invertebrate collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden .

Habitat and locality. Mud from 30–39 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 13'', E 11° 27' 31''), 21 August 2010, legit M. Clément (three females) ; soft mud from 30 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 25'', E 11° 27' 30''), 11 August 2011, legit O. Holovachov (three males and five females) ; soft mud from 44 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 37'', E 11° 27' 43''), 11 August 2011, legit O. Holovachov (nine males and 12 females) ; muddy sediment from 53 m deep, Skagerrak off the west coast of Sweden (N 58° 20' 06'', E 11° 09' 24''), 09 August 2011, legit O. Holovachov (three females) ; gravel, mud and algae from 30–70 m deep, Skagerrak off the west coast of Sweden (N 58° 22' 14'', E 11° 05' 00''), 09 August 2011, legit O. Holovachov (eight males and nine females) ; muddy sand from 25–50 m deep, Skagerrak off the west coast of Sweden (N 58° 22' 20'', E 11° 09' 26''), 09 August 2011, legit O. Holovachov (five males and five females) ; muddy sediment from 55–70 m deep, Skagerrak off the west coast of Sweden (N 58° 22' 19'', E 11° 04' 55''), 09 August 2011, legit O. Holovachov (three males and two females) .

Description. Adult. Body tapering anteriorly in pharyngeal region and posteriorly on tail; straight or 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 1.6–2.1 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 1.5–3.0 µm wide at mid-body; originating at level of metacorpus (posterior to first body pore) and extending posteriorly to middle of tail. Prominent body pores in sublateral position at both sides of lateral field present, arising from oval lateral epidermal gland cells; usually three pairs of body pores are present along pharyngeal region; several body pores scattered over rest of the body. Anteriormost body pore located at level of procorpus. Labial region rounded, continuous with body contour, lips fused. Inner and outer labial sensilla indistinct. Cephalic sensilla setiform, equal to 30–50% of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea round, located at level of middle of stoma. Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretory-excretory system indistinct. 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 cylindrical, its posterior part embedded in intestine. Tail similar in shape in both sexes (shorter and more curved ventrad in male), elongate-conoid, subcylindrical distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Setae absent. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with arcuate subcylindrical calamus and ovoid manubrium. Gubernaculum plate-like, with dorsocaudal apophysis. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, three to four unevenly spaced midventral tubular supplements extending for 70–111 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements weakly arcuate with claw-like tips pointing towards posterior end, the distance between second posteriormost and third posteriormost supplement is somewhat larger than the distance between first posteriormost and second posteriormost supplements. Posteriormost tubular supplement 17–25 µm anterior to cloaca, anterior to spicules. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of cloaca and usually six (three pairs) caudal setae arranged in two subventral and one subdorsal pairs.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 55–97 µm long (equal to 8.8–16.0% of total body length), located on right-hand side of intestine (n=8), posterior genital branch 55–90 µm long (equal to 9.6–14.9% of total body length), located on left-hand side of intestine (n=8). 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 short tube. Vagina straight, 0.2–0.3 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. Usually one tubular supplement located in front of anus, 21.5–33.0 µm anterior to anal opening; one female had two tubular supplements and one female had none. Rectum 1.1–1.6 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis (supplemented with literature data). Leptolaimus venustus is particularly characterised by the 541– 669 µm long body; rounded labial region continuous with body contour; cephalic setae 1.0–2.0 µm long; amphid located 8.5–11.5 µm from anterior end; first body pore located 27.0–36.0 µm from anterior end; lateral field originating 35.0–53.0 µm from anterior end; female with usually one preanal supplement, vagina without pars refringens, vulva midventral; male with three to four tubular and without alveolar supplements, tubular supplements weakly arcuate with claw-like tips pointing towards posterior end; spicules arcuate and 18.5–22.0 µm long.

Remarks. Current specimens agree well with the type specimen in general morphology, measurements and shape of amphids, the only difference being the reported length of spicules in the original description – 15 µm vs. 20–22 µm in recent specimens. When measured from the original illustrations, the actual spicule length is 18.5 µm, which would be considered as normal range for geographically distinct populations.

Figures

FIGURE 17. Leptolaimus venustus Lorenzen, 1972, male (A–C) and female (D–E). A: Anterior end, surface view; B: Pharyngeal region, median section; C: Male posterior region; D: Female tail; E: Female reproductive system (anterior part). Scale bar: A–E = 20 µm.

FIGURE 18. Leptolaimus quintus sp. n. (A–B), Leptolaimus lorenzeni (Boucher & de Bovée, 1972) comb. n. (C–D) and Leptolaimus venustus Lorenzen, 1972 (E–F). A, C, E: Entire female; B, D, F: Entire male. Scale bar: A–F = 50 µm.