Tylencholaimus discus

Golhasan, Behrouz, Heydari, Ramin & Peña-Santiago, Reyes, 2019, Description of Tylencholaimus discus sp. n. (Nematoda, Dorylaimida, Tylencholaimidae) from Iran, Zootaxa 4551 (3), pp. 379-384: 380-384

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Tylencholaimus discus

sp. n.

Tylencholaimus discus  sp. n.

( Figs 1–3View FIGURE 1View FIGURE 2View FIGURE 3)

Material examined: Twenty-five females from a single location, in variable, but often acceptable, state of preservation. Morphometrics: See Table 1.

Description. Female: Moderately slender (a = 22–25) nematodes of small size, 0.65–0.76 mm long. Body cylindrical, visibly tapering towards the anterior end, less so towards the posterior one as the tail is short and rounded. Upon fixation, body variably shaped, often curved ventrad, more occasionally straight or visibly sigmoid. Cuticle typical tylencholaimoid, 1–2 µm thick at anterior region, 2–3 µm in mid-body and 3.5–4.5 µm on tail; outer layer comparatively thin and with similar thickness throughout the body, nearly smooth under LM but showing distinct transverse striation under SEM; inner layer showing very irregular outline along the body, but more regular at posterior body region, especially at tail, where it becomes somewhat thicker; radial refractive elements distinct. Lateral chord 7.5–12 µm broad, occupying one-fourth to two-fifths (25–43%) of mid-body diameter. Lateral pores coarse, their total number (n=5) 14–19: 6–7 from anterior end to pharyngeal base, 4–6 from pharyngeal base to vagina, and 6–7 from vagina to anus. Lip region cap-like, offset from the adjacent body by a weak constriction, and with rounded margin; 1.6–2.1 times wider than high, and 21–27% of body diameter at neck base. SEM observations: lips amalgamated, with their inner perioral part totally fused and differentiated in a distinctly demarcated disc-like structure 4–4.5 µm broad and 1.5 µm high; both inner and outer labial papillae button-like, consisting of a central orifice surrounded by one annulus (inner) or two annuli (outer papillae); cephalic papillae a bit smaller than the labial ones; oral field relatively small as inner labial papillae are situated about half-way between oral aperture and the margin of perioral disc. Amphid cup-shaped, its aperture 3–4 µm long, occupying ca. one-half (43–57%) of lip region diameter. Odontostyle typical of the genus, 6.3–6.8 times as long as wide, equal to or slightly shorter than (0.8–1.0 times) lip region diameter, and 0.84–1.02% of body length. Guiding ring simple, at 4–6 µm from the anterior end. Odontophore 1.3–1.6 times the odontostyle in length, its base apparently more flanged than knobbed, but often difficult to distinguish. Pharynx consisting of a slender and weakly muscular anterior region enlarging rather abruptly into the basal expansion that is 7.8–8.4 times as long as wide, 3.5–4.1 times longer than body diameter at neck base, and occupies up to one-half (42–49%) of the total neck length; gland nuclei situated as follows: DO = 52–59, DN = 55–63, S 1 N 1 = obscure, S 1 N 2 = 75 (n = 1), S 2 N = 86–91. Cardia rounded conoid, 8.5– 14 x 8.5–11.5 µm. Genital system mono-prodelphic: anterior genital branch well developed, 95–176 µm long, with ovary 46–48 µm long, oviduct 42–79 µm long or 1.4–2.6 times the body diameter, a conspicuous sphincter between oviduct and uterus, and simple uterus 42–66 µm long or 1.4–2.2 times the body diameter; posterior genital branch very often reduced to a uterine sac 2–20 µm long or much shorter (0.1–0.6 times) than body diameter, and up to 3% of body length, but very occasionally (n = 2) consisting of uterus, sphincter and a small terminal mass all together measuring 35, 40 µm or 5, 6% of body length; vagina extending inwards 14–17 µm, occupying 47–61% of body diameter, pars proximalis 10–12.5 x 6 –7.5 µm with somewhat sigmoid walls surrounded by weak musculature, and pars distalis 3–4.5 µm; vulva a transverse slit ca 7 µm wide, with barely differentiated lips. Prerectum 3.3–5.7, rectum 0.8–1.1 anal body diameters long. Anus a small, ca. 2 µm long, transverse arched slit. Tail short and rounded, the inner cuticle layer showing a nearly regular outline and separated from the outer layer by a distinct lacuna; caudal pores two pairs, at the middle of tail, one subdorsal, another subventral.

Male: Unknown, with no trace of sperm cells in female genital tract.

Diagnosis: The new species is characterized by its 0.65–0.76 mm long body, lip region offset by weak constriction and 7–7.5 µm broad with a conspicuous perioral disc, odontostyle 6–7 µm long, odontophore 9–10.5 µm long and visibly flanged rather than knobbed, neck 230–259 µm long with anterior region weakly muscular and basal expansion 98–125 µm long or occupying 42–49% of total neck length, female genital system monoprodelphic, posterior branch reduced to a uterine sac 2–20 µm long or much shorter (0.1–0.6 times) than body diameter but very occasionally consisting of uterus, sphincter and a small terminal mass altogether measuring 35– 40 µm long, V = 65–74, tail short and rounded (13–17 µm, c = 41–57, c’ = 0.6–0.8), and unknown male.

Relationships: In having perioral disc, weakly muscular anterior pharyngeal region, mono-prodelphic female genital system, post-uterine sac, and tail short and rounded, the new species is very similar to T. constrictus Vinciguerra, 1986  , a European species (see detailed description by Peña-Santiago & Coomans 1994), and T. imperanus Mohilal & Dhanachand, 2003  (= T. lokus Mohilal & Dhanachand, 2003  ), an Indian species (see recent redescription by Ahad & Ahmad 2016). It can be distinguished from T. constrictus  by its smaller general size (body length 0.65–0.76, n = 26 vs 0.76–0.96 mm, n = 29), less slender body (a = 22–25 vs a only exceptionally under 25), more offset perioral disc with less differentiated oral field (compared to Figs. 8H–J by Peña-Santiago & Coomans 1994.), comparatively longer neck (b = 2.7–3.2 vs 3.2–4.1), and shorter female tail (13–17 vs 16–22 µm, c’ = 0.6– 0.8 vs c’ = 0.8–1.0). It differs from T. imperanus  in its larger general size (body length 0.65–0.76 vs 0.41–0.54 mm), more offset (vs nearly continuous) and broader (7–7.5 vs 6 µm) lip region, longer odontophore (9–10.5 vs 5– 6 µm), and visibly longer female tail (13–17 vs 10–11 µm).

Type locality and habitat: Northern Iran, Mazandaran Province, Nowshahr city, Kheyroodkenar forest (36°32′42.81′′N, 51°26′22.85′′E; 1510 m above sea level), in soil around the rhizosphere of unidentified grassesGoogleMaps  .

Type material: Female holotype and 14 female paratypes deposited in the Nematode Collection of the Department of Plant Protection, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. Eleven female paratypes at the Nematode Collection , University of Jaén, Spain  .

Etymology:The species name is a Latin substantive in apposition and refers to the characteristic disc-like structure present in lip region of the new species.