Oncholaimus langhovdensis, Shimada & Suzuki & Tsujimoto & Imura & Kakui, 2017

Shimada, Daisuke, Suzuki, Atsushi C., Tsujimoto, Megumu, Imura, Satoshi & Kakui, Keiichi, 2017, Oncholaimus langhovdensis sp. nov. (Nematoda: Enoplea: Oncholaimida), a New Species of Free-living Marine Nematode from Langhovde, Dronning Maud Land, East Antarctica, Species Diversity 22, pp. 151-159 : 152-156

Oncholaimus langhovdensis sp. nov.

( Figs 1–3 )

Material examined. Holotype. Male ( ICHUM 5311 ), whole mount . Paratypes. Four males ( ICHUM 5312–5315 ), four females ( ICHUM 5316 , 5317 , 5319 , and 5320), whole mounts . Non-type. An immature female ( ICHUM 5318 ), whole mount; a male and a female ( ICHUM 5321 and 5322, respectively), Au-coated SEM specimens .

Type locality and habitat. Intertidal sandy sediment, Langhovde (69°14′24.3″S, 39°42′55.8″E), Lützow-Holm Bay , Dronning Maud Land, East Antarctica .

Diagnosis. Oncholaimus langhovdensis sp. nov. is characterised by slender body (a= 75–91 in males, 56–70 in females), amphids located at posterior half of buccal cavity (59–82% of buccal cavity length), excretory pore located posterior to buccal cavity (2.2–2.8 times buccal cavity length from anterior body end), long conico-cylindrical tail without caudal papilla in both sexes (3.1–3.7 times abd in males, 2.6–3.1 times abd in females), short spicules (1.1–1.3 times abd and 33–38% of tail length), presence of Demanian system, short ductus uterinus (170–240 µm, 2.2–3.9 times vbd), and absence of terminal pores of main duct.

Measurements. See Table 2.

Description. Body ( Fig. 1A, B ) long, almost cylindrical, gradually tapering toward both ends. Cuticle thin and smooth. Head ( Figs 1C, D , 3A, B ) rounded, diameter at the level of cephalic setae 52–62% of mbd in males, 41–47% of mbd in females. Six lips each with an inner labial papilla ( Fig. 3A ). Six outer labial and four cephalic setae equal in length, arranged in a single circle. Amphids located at level of posterior half of buccal cavity (63–82% from anterior body end in males and 59–67% in females), width 19–32% of corresponding body diameter, consisting of a slit-like aperture and oval fovea. Buccal cavity large, barrel-shaped, length/width=2.1–2.3. Three well-developed teeth in buccal cavity, left subventral one largest and right subventral and dorsal ones equal in size. Cervical region ( Fig. 1E ) with sparse setae, tapering anteriorly, and almost cylindrical in posterior half. Ventral excretory pore at 2.2–2.8 times buccal cavity length from anterior body end (12–19% of pharynx length). Nerve ring at 41–54% of pharynx length. Ventral gland single, width 51–70% of corresponding body diameter, posterior end at 1.3–1.5 times pharynx length from anterior body end. Tail ( Figs 1F–I , 3C, D ) sexually dimorphic. Rectum 1.2–1.5 times abd and 33–42% of tail length in males and 0.7–0.8 times abd and 26–30% of tail length in females. Three caudal glands ( Fig. 2A ) situated at 10–24 times abd anterior to cloaca in males and 6–13 times abd anterior to anus in females.

Male. Reproductive system ( Fig. 2A ) diorchic. Testes opposed, situated on right or left side of intestine, anterior one outstretched and beginning at 23–31% of body length, and posterior one reflexed backward and ending at 65–82% of body length. Long glandular caecum along anterior testis reported in some Oncholaimus species (cf. Coomans and Heyns 1983) not observed. Spicules ( Figs 1F–H , 2B ) paired, equal in shape and size, almost cylindrical, distally acute and proximally expanded; 1.1–1.3 times abd and 33–38% of tail length (equal to or slightly shorter than rectum). Gubernaculum absent. Cloacal region ( Figs 1F–H , 3C, E ) swollen, with a very small pre-cloacal papilla ( Figs 1G , 3E ) immediately anterior to cloaca. Six to eight circum-cloacal setae on each ventrolateral side, three to five of them pre-cloacal and the others post-cloacal (in holotype, five pre-cloacal and three post-cloacal). Tail ( Figs 1F–H , 3C ) long, conicocylindrical, anterior 52–63% conical, ventrally bent in conical part and nearly straight in cylindrical part (diameter 22– 25% of abd). Ventral papilla in caudal region absent. A pair of short setae located at junction of conical and cylindrical parts of tail. Several pairs of extra caudal setae on cylindrical part. Two rows consisting of several setae on dorsal side of cloacal and caudal regions. Tip of tail slightly expanded, with a spinneret and two or three stout terminal setae.

Female. Reproductive system ( Fig. 2C ) monodelphic, posterior ovary absent. Anterior ovary 9–15% of whole body length, beginning at 49–62% from anterior body end. Uterus single, 8–12% of whole body length, beginning at 63–76% from anterior body end. Eggs elongated, length/ width=2.5–6.1, one to three in uterus. Vulva ( Fig. 3F ) slitlike, with swelling of body surface, situated at 71–84% from anterior body end. Demanian system ( Fig. 2C–E ) present. Ductus uterinus posterior to uterus, connecting to right side of main duct through uvette at 2.2–3.9 times vbd posterior to vulva. Ductus entericus anterior to uvette, connecting to dorsal side of intestine through osmosium at 1.1–2.4 times vbd posterior to vulva (1.2–2.1 times vbd anterior to uvette). Main duct inconspicuous in posterior body region, unbranched. Terminal pore indistinct on body surface. Tail ( Figs 1I , 3D ) 2.6–3.1 times abd long, conico-cylindrical but different in shape compared with that in males, anterior 69–77% conical and diameter of cylindrical part 15–21% of abd. Tip of tail not expanded. Several circumanal and caudal setae present.

Etymology. The specific name, langhovdensis , is an adjective derived from the type locality Langhovde.

Remarks. According to previous studies ( Filipjev 1918; Steiner 1921; Ditlevsen 1928; Cobb 1930; Kreis 1932, 1934; Allgén 1935; Gerlach 1958; Allgén 1959; Wieser 1959; Chitwood 1960; Filipjev 1968; Vitiello 1970; Belogurov et al. 1975a, b; Coles 1977; Belogurov and Belogurova 1978; Tsalolikhin 1979; Belogurov and Fadeeva 1980a, b; Belogurov et al. 1980; Smolyanko and Belogurov 1987; Pavlyuk 1991; Smolyanko and Belogurov 1991; Pastor de Ward 1993; Platonova and Kulangieva 1995; Huang and Zhang 2006; Leduc 2008; Shimada et al. 2009; Chen and Guo 2014), males of 35 species of the genus Oncholaimus sensu lato have conico-cylindrical tails (see taxonomic key below). Five species, i.e., Oncholaimus chiltoni Ditlevsen, 1930 , O. gladius Gerlach, 1956 , O. longissimus Allgén, 1959 , O. manilius Gerlach, 1957 , and O. steineri Ditlevsen, 1928 , are not included in spite of their conico-cylindrical tails, because O. chiltoni should be transferred to Viscosia de Man, 1890 based on its larger right subventral tooth than left one ( Ditlevsen 1930), and the other four species should be transferred to Metoncholaimus Filipjev, 1918 based on the presence of gubernacula ( Ditlevsen 1928; Gerlach 1956, 1957; Allgén 1959)

Oncholaimus langhovdensis sp. nov. closely resembles 11 of them based on the conico-cylindrical tails present in males and amphid (posterior half of buccal cavity) and excretory pore positions (2–3 times the buccal cavity length from the anterior body end), the short spicules (1.1–1.3 times abd and 30–40% of the tail length), and Demanian system present in females. Oncholaimus langhovdensis sp. nov. is easily distinguished from three anomalous species: O. nigrocephalatus Cobb, 1930 (with three masses of pigment granules at the base of the buccal cavity) ( Cobb 1930; Timm 1952); O. lanceolatus Vitiello, 1970 (greatly elongated tail with a filiform posterior part) ( Vitiello 1970); and O. paropisthonchus Belogurov and Belogurova, 1978 (three teeth almost equal in size) ( Belogurov and Belogurova 1978). It also differs from O. apostematus Wieser, 1959 , O. olium (Belogurov et al., 1975) , and O. tchesunovi ( Platonova and Kulangieva, 1995) in the main duct of the Demanian system (single, unbranched duct without determinable pore in O. langhovdensis sp. nov. vs. branched duct with several pores in the three species) ( Wieser 1959; Belogurov et al. 1975a, b; Zhang and Platt 1983; Platonova and Kulangieva 1995), from O. malgassus Gerlach, 1958 and O. sheri ( Chitwood, 1960) in the female tail shape (anterior part tapering just posterior to the anus and diameter of the cylindrical part less than 1/4 of abd vs. anterior part tapering from the preanal region in O. sheri , and cylindrical part approximately 1/2 wide of abd in O. malgassus ) ( Gerlach 1958; Chitwood 1960), from O. opisthonchus Filipjev, 1927 and O. ushakovi Filipjev, 1927 in the more slender body shape (mbd=55– 60 µm, a= 75.4–90.6 in males vs. mbd=140 µm, a=37.1 and mbd=95–130 µm, a=43–59, respectively) ( Filipjev 1927), and from O. paracampylocercoides ( Smolyanko and Belogurov, 1991) in the smaller body size and longer pharynx (4.4– 5.4 mm, b=7.0–8.1 vs. 6.2–7.2 mm, b=9.4–11.8) ( Smolyanko and Belogurov 1991).

Oncholaimus langhovdensis sp. nov. resembles 13 congeners known only by females. Oncholaimus langhovdensis sp. nov. most closely resembles four of them in the conicocylindrical tail, amphid and excretory pore positions, and the Demanian system with a single main duct. However, it can be distinguished from O. marinus Schulz, 1932 and O. unicus ( Belogurov and Belogurova, 1978) in the tail length (2.6–3.1 times abd vs. 6.5 times abd and 1.4–1.5 times abd, respectively) ( Schulz 1932; Kreis 1934; Timm 1954; Belogurov and Belogurova 1978) and from O. vanderlandi Loof, 1973 and O. jessicae Coomans and Heyns, 1986 in the position of the uvette (174–239 µm= 2.2–3.9 times vbd posterior to vulva vs. 390 µm= 8 times vbd, and 596–856 µm= 13–20 times vbd, respectively) ( Loof 1973; Coomans and Heyns 1986).

Figures

Fig. 1. Oncholaimus langhovdensis sp. nov. Males ICHUM 5311 (holotype; A, C, E, F), 5312 (D), 5313 (G), 5314 (H), and a female ICHUM 5316 (B, I). A, male body; B, female body; C, head, ventral view; D, head, lateral view; E, anterior region; F, male tail, lateral view; G, male tail, lateral view; H, male tail, ventral view; I, female tail, lateral view. Abbreviations: a.t., anterior testis; e.p., excretory pore; i., intestine; n.r., nerve ring; ov., ovary; p., papilla; p.t., posterior testis; ut., uterus; v.d., vas deferens; v.g., ventral gland. Scale bars: A, B, 1mm; C, D, 20µm; E, 100µm; F–I, 50µm.

Fig. 2. Oncholaimus langhovdensis sp. nov. Male ICHUM 5311 (holotype; A, B), females ICHUM 5316 (C, D) and 5317 (E). A, testes; B, left spicule, lateral view; C, female posterior region; D, uvette and osmosium, right lateral view; E, uvette and osmosium, ventral view. Abbreviations: a.t., anterior testis; d.e., ductus entericus; d.u., ductus uterinus; e., egg; i., intestine; os., osmosium; ov., ovary; p.t., posterior testis; ut., uterus; uv., uvette; v., vulva; v.d., vas deferens. Scale bars: A, C, 500µm; B, 10µm; D, E, 50µm.

Fig. 3. Oncholaimus langhovdensis sp. nov., SEM images. A female ICHUM 5322 (A, B, D, F) and a male ICHUM 5321 (C, E). A, head, anterior view; B, head, lateral view; C, male tail, lateral view; D, female tail, lateral view; E, male cloacal region, ventral view; F, vulva, ventrolateral view. Scale bars: A, B, E, F, 10µm; C, D, 50µm.