Leptolaimus septempapillatus Platt, 1973

Holovachov, Oleksandr & Boström, Sven, 2013, Swedish Plectida (Nematoda). Part 4. The genus Leptolaimus de Man, 1876, Zootaxa 3739 (1), pp. 1-99 : 65-71

Leptolaimus septempapillatus Platt, 1973

( Figs 29 , 30 , 31 A–B ; Table 19)

Material examined. 41 males and 35 females (slides # 130915–130928) 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 (five males and eight 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 (six males and four 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 (19 males and 13 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 and one female) ; 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 (two males and two 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 (two males and four females) ; 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 (four males and two 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 (two 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 2.6–3.2 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 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 labial sensilla indistinct. Outer labial sensilla indistinct under the light microscope, small papilliform with terminal pore as seen under SEM; located on the anterior surface of lips. Cephalic sensilla setiform, equal to 40–60% 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, gradually narrowing distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Long setae emerging through all body pores over entire body. 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, seven (rarely eight) evenly spaced midventral tubular supplements extending for 303–379 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements weakly arcuate in shape, with dentate tips. Posteriormost tubular supplement 31–40 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 unpaired seta located on the left subdorsal side just posterior to cloaca. 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 145–183 µm long (equal to 17.0–20.3% of total body length), located on right-hand side of intestine (n=8), posterior genital branch 121–186 µm long (equal to 14.1–20.7% of total body length), located on left-hand side of intestine (n=8). Oviduct a narrow tube. Two offset, oval, sac-like spermathecae located on each (right and left) side of each (anterior and posterior) gonoduct. Spermathecae and oviducts filled with oval spermatozoa. Uterus a wide and long tube. Vagina straight, 0.2–0.3 times vulval body diameters long; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae present, each side is semicircular in shape. Vulva midventral, a transverse slit with small liplets as seen under SEM. Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Supplements absent. Rectum 0.8–1.1 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis (supplemented with literature data). Leptolaimus septempapillatus is particularly characterised by the 762–965 µm long body; rounded labial region weakly offset from body contour; cephalic setae 2.0–3.0 µm long; amphid located 8.0–14.0 µm from anterior end; first body pore located 29–39 µm from anterior end; lateral field originating 57.0–67.0 µm from anterior end; female without supplements, vagina with semicircular pars refringens, vulva midventral; male with seven (rarely eight) tubular and without alveolar supplements, tubular supplements weakly arcuate with dentate tips; spicules arcuate and 22.0–28.5 µm long.

Remarks. Current specimens agree well with the type specimens in general morphology, body size, measurements, shape of anterior end and amphids, number and shape of supplements, shape of spicules and gubernaculum. The only differences being slightly more anterior position of the amphid (8.0–11.0 µm vs. 13.0– 14.0 µm from anterior end in type specimens) and slightly longer spicules (26.0–28.5 µm vs. 22.0–26.0 µm long in type specimens). Unfortunately, the original description of this species is insufficiently illustrated to allow any further comparison. This species is very similar to Leptolaimus elegans (described below) and was considered a junior synonym of it ( Fadeeva & Mordukhovich, 2007; Platt & Warwick, 1988), however, present study revealed consistent differences in male and female morphology between both species (See Table 22). L. septempapillatus as re-described here, can be separated from L. elegans based on following features: wider labial region (4–6 µm vs. 3.5–4 µm in L. elegans ), relatively shorter pharynx (b=5.6–6.5 vs. b= 4.1–5.4 in L. elegans ), longer spicules (22–29 µm vs. 20–24 µm in L. elegans ), orientation of vulva (midventral vs. right-subventral in L. elegans ), presence of pars refringens vaginae (vs. absent in L. elegans ).

Figures

FIGURE 29. Leptolaimus septempapillatus Platt, 1973, male (A–C) and female (D–E). A: Anterior end, surface view; B: Pharyngeal region, median section; C: Male posterior region, anterior and posterior parts; D: Female tail; E: Female reproductive system (anterior part). Scale bar: A–E = 20 µm.

FIGURE 30. Leptolaimus septempapillatus Platt, 1973, female (A–B, D) and male (E–I). A: Anterior end, subventral view; B: Anterior end, ventral view; C: Anterior end, apical view; D: Female vulval region; E: Male cloacal region; F: Male caudal region; G: Most posterior supplement in male; H: Male cloacal region with protruding spicules; I: Male posterior body end. Scale bars: A–C, G = 5 µm, D–E, H = 10 µm, I = 50 µm.

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.