Leptolaimus mixtus Lorenzen, 1972

Holovachov, Oleksandr & Boström, Sven, 2013, Swedish Plectida (Nematoda). Part 4. The genus Leptolaimus de Man, 1876, Zootaxa 3739 (1), pp. 1-99 : 29-32

Leptolaimus mixtus Lorenzen, 1972

( Figs 7 C–D , 12 ; Table 8)

Material examined. 47 males and 42 females (slides # 129950–129961) 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 (four males and 15 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 (two males) ; 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 (10 males and nine females) ; algae from 20–40 m deep, Skagerrak off the west coast of Sweden (N 58° 21' 49'', E 11° 04' 42''), 09 August 2011, legit O. Holovachov (three males and two females) ; coarse gravel from 30–50 m deep, Skagerrak off the west coast of Sweden (N 58° 17' 58'', E 11° 10' 05''), 09 August 2011, legit O. Holovachov (three males and one female) ; coarse sediment with algae from 45–55 m deep, Skagerrak off the west coast of Sweden (N 58° 17' 32'', E 11° 11' 24''), 09 August 2011, legit O. Holovachov (25 males and 15 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 1.7–2.1 µm wide at mid-body, without ornamentation. Lateral field present, consists of single ala (two incisures), 1.0–1.5 µm wide at mid-body; originating at level of procorpus (anterior to or at level with 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 four 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 40–70% of labial region diameter. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea round, located at level of anterior 2/5th of stoma. Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretory-excretory system obscure. 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, gradually narrowing distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Four short setae emerging through first, second, third and fourth pairs of body pores. Reproductive system diorchic; anterior testis outstretched; posterior one reflexed. Spicules paired, symmetrical, with arcuate subcylindrical calamus and ovoid manubrium. Gubernaculum plate-like, with dorsal apophysis bending anteriorly. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, four evenly spaced midventral tubular supplements extending for 138–176 µm from cloaca towards anterior end; two alveolar supplements. Out of 30 examined males, only two males had three alveolar supplements instead of the usual two. Tubular supplements almost straight, with blunt expanded tips. Posteriormost tubular supplement 28– 41 µm anterior to cloaca, anterior to spicules. Alveolar supplements with inner sclerotized ring. Anteriormost alveolar supplement 341–407 µm from anterior end, at level of posterior part of intestine. Sublateral precloacal and caudal sensilla present: two (one pair) precloacal setae at level of cloaca 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 76–138 µm long (equal to 10.6–17.7% of total body length), located on right-hand side of intestine (n=5), posterior genital branch 79–131 µm long (equal to 9.4–16.5% of total body length), located on left-hand side of intestine (n=5). 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 usually left-ventrosublateral (n=6), less commonly right-ventrosublateral (n=2). Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Supplements absent. Rectum 1.6–2.1 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis (supplemented with literature data). Leptolaimus mixtus is particularly characterised by the 659–845 µm long body; rounded labial region continuous with body contour; cephalic setae 2.0–5.0 µm long; amphid located 6.0–9.0 µm from anterior end; first body pore located 24.0–36.0 µm from anterior end; lateral field originating 20.0–32.0 µm from anterior end; female without supplements, vagina without pars refringens, vulva left- or right-ventrosublateral; male with four tubular and two (rarely three) alveolar supplements, tubular supplements almost straight with blunt expanded tips, alveolar supplements with sclerotized inner ring; spicules arcuate and 22.0–30.0 µm long.

Remarks. Current material agrees well with the type specimens in general morphology, measurements, number and shape of supplements, shape of spicules and gubernaculum. Specimens from Skagerrak are also very similar to L. mixtus from Oosterschelde, the Netherlands ( Holovachov & Boström, 2004), with only difference being details of the vagina, which is described as having pars refringens. Male specimen from Oosterschelde has three alveolar supplements, which is not common in males from Skagerrak – only two out of 30 examined males from Skagerrak had three alveolar supplements, instead of two.

Figures

FIGURE 7. Leptolaimus secundus sp. n. (A–B), Leptolaimus mixtus Lorenzen, 1972 (C–D) and Leptolaimus quartus sp. n. (E). A, C: Entire female; B, D, E: Entire male. Scale bar: A–E = 50 µm.

FIGURE 12. Leptolaimus mixtus 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.