Tylencholaimus mirabilis ( Bütschli, 1873 )

Islam, Md Niraul & Ahmad, Wasim, 2021, Five new and five known species of the genus Tylencholaimus de Man, 1876 (Nematoda: Dorylaimida: Tylencholaimoidea) from Western Ghats of India, European Journal of Taxonomy 774 (1), pp. 58-105 : 60-64

Tylencholaimus mirabilis ( Bütschli, 1873)

Figs 1–2 , Table 1

Tylenchus mirabilis Bütschli, 1873: 44–45 .

Discomyctus brevicaudatus Tarjan, 1953: 52–54 .

Tylencholaimus mirabilis – de Man 1876: 43; 1880: 66; 1884: 104–105. — Loof & Jairajpuri 1968: 321–325. — Vinciguerra 1986: 112. — Peña-Santiago & Coomans 1994b: 199–206.

Dorylaimellus mirabilis – Thorne 1939: 140.

Dorylaimellus (Tylencholaimus) mirabilis – Meyl 1953: 94

Tylencholaimus brevicaudatus – Tarjan 1956: 91. — Loof 1961: 246–247. — Coomans 1962: 146–149.

Material examined

INDIA • 26 ♀♀, 2 ♂♂; Tamil Nadu State, Nilgiris district, Ooty, Dodabetta Peak Road ; 11º40.1′99.9″ N, 76º73.5′36.9″ E; 10–15 cm depth; 28 Mar. 2018; soil samples collected from around the roots of shrubs (unidentified); slides reference number AMU/ZD/NC/ Tylencholaimus mirabilis /1–10 .

Description

Female

Small sized nematodes, slightly curved ventrad upon fixation; body cylindrical, tapering gradually towards both extremities but more so towards the anterior end. Cuticle with two distinct layers, 1.0– 1.5 µm thick at anterior region, 2.0–2.5 μm at midbody and 3.0–4.0 μm on tail. Outer cuticle thin, finely striated; inner layer thick, its outline somewhat irregular, with distinct radial refractive elements. Lateral chords occupying about 15–25% of midbody diameter. Body pores distinct, lateral pores: one at odontostyle-odontophore region, 2–5 in neck region, 5–8 at pharyngeal base to vulva and 5–10 in post-vulval region; dorsal body pores: one at odontostyle-odontophore region, 1–3 in neck region, 3 from pharyngeal base to vulva and 1–2 in post-vulval region; ventral body pores: 1–3 in neck region, 1–3 from pharyngeal base to vulva and 3 in post-vulval region. Lip region cap-like, offset by deep constriction, 1.8–2.2 times as wide as high or about ⅓ of the body diameter at neck base. Lips rounded, amalgamated, inner part slightly elevated. Labial and cephalic papillae distinct but not interfering with the labial contour. Amphids cup-shaped, their aperture occupying about ⅓ to ½ of lip region diameter. Stoma a truncate cone. Odontostyle 0.7–0.9 times the lip region diameter long, its aperture about ¼ to ⅓ of its length. Odontophore rod-like, with distinct basal swelling, 1.2–1.6 times the odontostyle length. Guiding ring simple, refractive, at 0.6–0.8 times the lip region diameter from anterior end. Pharynx consisting of a slender, weakly muscular anterior part, expanding abruptly into a cylindrical basal bulb, with thick-walled lumen, separated by a constriction, occupying about 41–46% of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 59–62, DN = 62–65, DO–DN = 1.7–3.7, S1N1 = 72–76, S1N2 = 76–80, S2N = 89–91, S2O = 90–93. Nerve ring at 34–42% of neck length from anterior end. Cardia rounded to conoid, about ⅓ to 2/5 of the corresponding body diameter long.

Genital system monodelphic-prodelphic. Ovary reflexed, measuring 46–127 μm long, rarely extending beyond the oviduct-uterus junction (n = 4); oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 38–91 μm, its proximal and distal parts not differentiated. Oviduct-uterus junction marked by weak sphincter. Uterus short and tubular, measuring 28–47 μm long. Posterior genital branch reduced to very small sac-like structure, measuring 5.0–8.5 μm long or about ¼ of midbody diameter. Sperm cell absent. Vagina cylindrical, extending inward, 11–15 μm, or about ⅓ to ½ (35–50%) of midbody diameter; pars proximalis vaginae 6.5–9.5 × 6.0–8.0 μm, encircled by circular muscles; pars distalis vaginae 4.0–5.5 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 5.6–8.8 and rectum 1.0–1.5 anal body diameter long. Tail convex-conoid with bluntly rounded terminus, 1.2–1.8 times anal body diameter long, with a pair of caudal pores on each side.

Male

General morphology similar to that of female, except for posterior region being more ventrally curved. Genital system diorchic, testes opposed, sperm cell spindle-shaped. In addition to adcloacal pair at 7.0–8.0 µm from cloacal aperture, there are four ventromedian supplements, located outside the range of spicules, first ventromedian supplement at 37–38 μm from adcloacal pair, second at 7.0–8.0 μm from first, third at 22–23 μm from second and fourth at 10–11 μm from third ventromedian supplement. Spicules typically dorylaimoid, curved ventrad, relatively robust, 4.0–4.4 times as long as wide and 1.2– 1.3 times as long as body diameter at level of cloacal aperture, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 123–125º, head occupying about 22% of total spicules length, median pieces 9.5–10.2 times as long as wide, occupying about 30% of the spicules maximum width, reaching the spicules tip, posterior end 3.0–3.5 μm wide. Lateral guiding pieces distinct, rod-like, 3.4–4.0 times as long as wide or ¼ of the spicules length. Prerectum 6.0–7.0 and rectum 1.2–1.5 times cloacal body diameter long. Tail short, convex-conoid, with bluntly rounded terminus, 1.4 cloacal body diameter in length, with a pair of caudal pores on each side.

Remarks

Bütschli (1873) described Tylenchus mirabilis from Germany for which de Man (1876) proposed the genus Tylencholaimus with T. mirabilis as its type species. The type specimens were not preserved and the identity of the species remained uncertain. De Man (1880, 1884) collected specimens from soil near Apeldoorn, The Netherland in July, 1879 and described them as Tylencholaimus mirabilis . Tarjan (1953) described Discomyctus brevicaudatus from Rhode Island, United States, which he later ( Tarjan 1956) transferred to Tylecholaimus. Coomans (1962) redescribed T. brevicaudatus from Belgium and considered it closely similar to T. mirabilis ( Bütschli, 1873) . Loof & Jairajpuri (1968) in their revision of the genus Tylencholaimus , redescribed this species based on seven females from the type locality and one male from Switzerland, and designated neotype as well as topotype from these specimens. They also agreed with de Man’s (1876) opinion that T. mirabilis is the type species of the genus Tylencholaimus . Vinciguerra (1986) described this species from Italy, while Peña-Santiago & Coomans (1994b), in their revision of the genus Tylencholaimus , made a detailed study of the type population and of another population collected from Spain. The morphometrics of the present specimens collected from India conform well with the type population, except in having slightly smaller spicules (27 vs 31 μm). The present specimens also conform well with populations described earlier by Tarjan (1953), Loof (1961) and Coomans (1962), except for the presence of males (vs absent). The present specimens also conform with Spanish and Italian populations described by Peña-Santiago & Coomans (1994b) and Vinciguerra (1986). This is the first report of T. mirabilis from India.

Figures

Fig. 1. Tylencholaimus mirabilis (Bütschli, 1873). A. Entire female. B. Entire male. C. Female anterior region. D. Female anterior region showing amphid. E. Female pharyngeal region. F. Female expanded part of pharynx. G–H. Female genital system. I. Female posterior region. J. Male posterior region. K. Spicule. L. Lateral guiding piece.

Fig. 2. Tylencholaimus mirabilis (Bütschli, 1873) (LM photographs). A–B. Female anterior region. C. Female anterior region showing amphid. D. Female pharyngeal region. E. Female expanded part of pharynx. F. Female genital system. G. Vulval region. H. Female posterior region. I. Female posterior end. J–K. Male posterior end. Scale bars: A–C, E–G, I–K = 10 μm; D, H = 20 μm.