Leptolaimus elegans ( Schuurmans Stekhoven & De Coninck, 1933 ) Gerlach, 1958

Holovachov, Oleksandr & Boström, Sven, 2013, Swedish Plectida (Nematoda). Part 4. The genus Leptolaimus de Man, 1876, Zootaxa 3739 (1), pp. 1-99 : 71-74

Leptolaimus elegans ( Schuurmans Stekhoven & De Coninck, 1933) Gerlach, 1958

( Figs 31 C–D , 32 ; Table 20)

Material examined. 17 males and 86 females (slides # 130932–130940, 130942, 130944–130947) deposited in the general invertebrate collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden .

Habitat and locality. Muddy clay from 52.5 m deep, near Landsort Island, Baltic Sea off the east coast of Sweden (N 58° 46' 00'', E 17° 49' 52''), 26 May 2011, legit C. Raymond (one male and nine females) ; mud from the bottom, Bothnian Gulf off the east coast of Sweden (N 60° 36' 05'', E 18° 44' 55''), 17 May 2011, legit J. Albertsson (seven males and 32 females) ; mud from 38 m deep, Bothnian Gulf off the east coast of Sweden (N 60° 24' 21'', E 18° 29' 10''), 19 May 2011, legit J. Albertsson (two males and nine females) ; mud from 86 m deep, Bothnian Gulf off the est coast of Sweden (N 62° 49' 07'', E 18° 23' 44''), 23 May 2011, legit J. Albertsson (seven males and 36 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 1.0–1.5 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 2.0–3.0 µm wide at mid-body; originating at level of metacorpus (posterior to first body pore) and extending posteriorly to proximal part 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, and one at level of cardia; numerous 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 30–60% 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 present; excretory pore located posterior to nerve ring. 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 (more curved ventrad in male), elongate-conoid to subcylindrical, gradually narrowing distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Long setae emerging through first, second and third pairs of body pores. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with arcuate cylindrical calamus and ovoid manubrium. Gubernaculum plate-like, with dorsal apophysis. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, five evenly spaced midventral tubular supplements extending for 183–214 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements weakly arcuate in shape, with dentate tips. Posteriormost tubular supplement 45–57 µm anterior to cloaca, anterior to spicules. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of spicules and usually eight (four pairs) caudal setae arranged in two subventral and two subdorsal pairs. One subventral pair of papilliform sensilla located at the bases of the second (from cloaca) pair of caudal setae.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 61–132 µm long (equal to 10.8–21.2% of total body length), located on right-hand side of intestine (n=7), posterior genital branch 78–122 µm long (equal to 13.7–20.0% of total body length), located on left-hand side of intestine (n=7). Oviduct a narrow tube. Two offset, oval, sac-like spermathecae located on each (right and left) side of each (anterior and posterior) gonoduct. Spermathecae often filled with oval spermatozoa. Uterus a wide and short tube. Vagina straight; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae absent. Vulva right ventrosublateral. Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Supplements absent. Rectum 1.4–1.9 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis (supplemented with literature data). Leptolaimus elegans is particularly characterised by the 493– 800 µm long body; rounded labial region continuous with body contour; cephalic setae 1.5–4.0 µm long; amphid located 8.0–12.0 µm from anterior end; first body pore located 24.0–36.0 µm from anterior end; lateral field originating 50.0–75.0 µm from anterior end; female without supplements, vagina without pars refringens, vulva right ventrosublateral; male with five–eight tubular and without alveolar supplements, tubular supplements weakly arcuate with dentate tips; spicules arcuate and 20.0–24.0 µm long.

Remarks. Current specimens agree well with the type specimen in general morphology, measurements and shape of amphids, the only difference being shorter cephalic setae (1.5–2.0 µm vs. 4.0 µm in type specimen). Unfortunately, the original description of this species is insufficiently illustrated and does not include any data about males to allow any further comparison. Therefore, our identification is mainly based on the redescription of L. elegans published by Lorenzen (1972b). When comparing to specimens described by Lorenzen (1972b), present specimens mainly differ in having constant number of supplements in males (5 vs. 5–8), shorter body (493–622 µm vs. 635–800 µm), shorter cephalic setae (1.5–2.0 µm vs. 3.0–3.5 µm). On the other hand, other body measurements, shape and length of spicules, shape of gubernaculum, number and arrangement of sensilla along pharyngeal region and on male tail are identical between populations.

Figures

FIGURE 31. Leptolaimus septempapillatus Platt, 1973 (A–B) and Leptolaimus elegans (Schuurmans Stekhoven & De Coninck, 1933) Gerlach, 1958 (C–D). A, C: Entire female; B, D: Entire male. Scale bar: A–D = 50 µm.

FIGURE 32. Leptolaimus elegans (Schuurmans Stekhoven & De Coninck, 1933) Gerlach, 1958, 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.