Leptolaimus quintus, 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 : 46-49

Leptolaimus quintus sp. n.

( Fig. 18 A–B , 20 ; Table 13)

Type material. Holotype male (slide # Type-8476) and nine female paratypes (slides # Type-8476 - Type-8477) deposited in the invertebrate type collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden.

Additional material. Four males and 14 females (slides # 130567–130572) deposited in the general invertebrate collection of the Department of Zoology , Swedish Museum of Natural History, Stockholm, Sweden .

Type locality. 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 (one male and nine females) .

Additional localities. 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 (one male and 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 (one female) ; 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 (three males and ten females) .

Etymology. The specific epithet " quintus " is translated as " the fifth " and refers to the sequential number of the new species described in this publication.

Description. Adult. Body tapering anteriorly in pharyngeal region and posteriorly on tail; straight or weakly 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 1.5–2.0 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 procorpus (posterior to first body pore) and extending posteriorly to posterior third 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 posterior third 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), elongateconoid, gradually narrowing distally. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Long setae emerging through all pairs of body pores throughout the body. 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. Accessory apparatus composed of one midventral precloacal papilliform sensillum located on anterior cloacal lip, 8–10 midventral tubular supplements extending for 281–341 µm from cloaca towards anterior end, the gap between the posteriormost fourth (or fifth) and posteriormost fifth (or sixth) tubules is somewhat bigger than between the other tubules; alveolar supplements absent. Tubular supplements weakly arcuate with anchor-like tips. Posteriormost tubular supplement 24.0–30.0 µm anterior to cloaca, anterior to spicules. 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 34–56 µm long (equal to 6.8–12.4% of total body length), located on right-hand side of intestine (n=9), posterior genital branch 37–54 µm long (equal to 7.6–11.9% of total body length), located on left-hand side of intestine (n=9). 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 tube. Vagina straight, 0.3 times vulval body diameters long; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae absent. Vulva right-sublateral, recessed, often covered with distinct refractive copulatory plug. Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Two tubular supplements present: one anterior located just posterior to cardia, 107–123 µm from anterior end, and one posterior located in front of anus, 21.5–28.5 µm anterior to anal opening. Rectum 0.9–1.6 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis. Leptolaimus quintus sp. n. is particularly characterised by the 443–528 µm long body; rounded labial region continuous with body contour; cephalic setae 1.0–2.0 µm long; amphid located 7.0–10.0 µm from anterior end; first body pore located 18.0–28.5 µm from anterior end; lateral field originating 25.0–41.0 µm from anterior end; female with two tubular supplements (one just posterior to cardia and one in front of anus), vagina without pars refringens, vulva right-sublateral; male with 8–10 tubular and without alveolar supplements, tubular supplements weakly arcuate with anchor-like tips; spicules arcuate and 17.0–22.0 µm long.

Relationships. The new species belongs to a group of species, females of which have tubular supplements along the pharyngeal region and in front of cloaca, e.g.: L. cangionensis (Gagarin & Nguyen Vu Thanh, 2007) comb. n., L. rivalis (Gagarin & Nguyen Vu Thanh, 2007) comb. n., L. lorenzeni , L. harpaga ( Boucher & de Bovée, 1972) comb. n., L. pellucidus and L. sergeevae ( Ürkmez & Brennan, 2013) comb. n.. Leptolaimus quintus sp. n. differs from L. cangionensis , L. rivalis , L. lorenzeni , L. harpaga and L. pellucidus in having males with 4–6 supplements in the anterior group arranged posterior to cardia (vs. either single supplement located posterior to cardia in L. cangionensis , L. rivalis , L. lorenzeni , L. harpaga or 1–3 supplements located along the pharyngeal region in L. pellucidus ), and from L. sergeevae in having only two tubular supplements in females (vs. five in L. sergeevae ).

Figures

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.

FIGURE 20. Leptolaimus quintus sp. n., holotype male (A–C) and paratype 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.