Discotylenchus biannulatus, Konani & Panahandeh & Pourjam & Álvarez-Ortega & Pedram, 2018

Konani, Ehsan, Panahandeh, Yousef, Pourjam, Ebrahim, Álvarez-Ortega, Sergio & Pedram, Majid, 2018, Two rare species of tylenchids, Discotylenchus biannulatus n. sp. and Labrys chinensis Qing & Bert, 2018 (Nematoda: Tylenchidae) from western Iran, Zootaxa 4413 (2), pp. 260-270 : 261-264

Discotylenchus biannulatus n. sp.

( Figs. 1–3 )

Description. Measurements. See Table 1.

Female: Body straight to slightly ventrally curved after heat relaxation. Cuticle finely annulated, annules ca. 1–2 µm wide at mid-body. Lateral fields with four incisures, outer lines partly areolated at anus/tail region in SEM images, 2–3 µm wide at mid-body, approximately 20% of body diameter. Lip region continuous with body contour, 5–6 µm wide and 3–4 µm high, dorso-ventrally flattened, smooth, having two annuli in the proximal end and a prominent perioral disc under SEM. Amphidial openings as longitudinal slits on lateral sides of the head. Stylet delicate, with conus shorter than the shaft comprising ca 32.7% of stylet total length; knobs small, slightly sloping posteriad. Dorsal gland orifice (DGO) 1–2 µm from base of stylet. Procorpus slender, joining to an ellipsoid muscular metacorpus with distinct valvular apparatus, located at 39–43% of total pharynx length; isthmus elongated and narrow; and basal bulb with slight variation in shape, saccate to bottle-shaped, 14–18 µm long and 7–9 µm wide. Cardia small. Nerve ring encircling anterior half of isthmus, 63–68 µm from anterior end. Excretory pore situated at the level of the middle of the isthmus, posterior to hemizonid. Deirids distinct and situated 4–6 annuli posterior to excretory pore. Reproductive system monodelphic-prodelphic, composed of an outstretched ovary occupying 23–26% of the body length, oocytes mainly in a single row, oviduct short, spermatheca rounded and empty, crustaformeria hardly visible, uterus tubular, vagina straight with thin walls; PUS length about 0.6–0.8 times vulval body width, vulva a transverse slit lacking any differentiation. Tail filiform, gradually tapering to a more or less pointed end.

Male: not found.

Type habitat and locality. Recovered from the rhizosphere of wheat, Giloran region, city of Khorram-Abad, Lorestan province, western Iran. GPS coordinates: N 33 27 ʹ 51.53 and E 48 18 ʹ 17.99.

Etymology. The specific epithet refers to two unusual annuli at the anterior end of the cephalic region of the new species.

Type material. Holotype and five paratypes deposited at the Ghent University Museum, Zoology Collection, Belgium.

Diagnosis and relationships. Discotylenchus biannulatus n. sp. is characterized by its dorso-ventrally flattened smooth lip region having two proximal annuli and a distinct rectangular perioral disc, short longitudinal amphidial slits, lateral field with four incisures, stylet 9–10 µm long, empty spermatheca and short PUS, and filiform female tail with pointed end.

With four lines in the lateral field, the new species can be compared with three known species of the genus: D. attenuatus Siddiqi, 1980 , D. brevicaudatus and D. discretus . The new species can be distinguished from these species by its smooth cephalic region with two annuli at the anterior end. In addition, Discotylenchus biannulatus n. sp. differs from D. attenuatus by having longer body (675–708 vs 330–400 µm), longer stylet (9–10 vs 6.0–6.5 µm), longer tail (155–161 vs 68–96 µm) and higher cʹ ratio (14.1–16.1 vs 9–12). It can be distinguished from D. brevicaudatus by its dorso-ventrally flattened cephalic region (vs rounded, according to SEM data provided by Yaghoubi et al. 2016), longer body (675–708 vs 320–466 µm), longer stylet (9–10 vs 6–8 µm), more anteriorly located vulva (V = 59.5–60.6 vs 68–73), longer tail (155–161 vs 35–77 µm), smaller c ratio (4.2–4.5 vs 5.9–9.8), higher cʹ ratio (14.1–16.1 vs 4.5–9.6) and filiform tail with pointed end (vs thick with rounded end). Finally, compared to D. discretus , the new species has dorso-ventrally flattened cephalic region (vs rectangular, smooth, according to SEM data provided by Yaghoubi et al. 2016), longer stylet (9–10 vs 7–9 µm), more anteriorly located vulva (V = 59.5–60.6 vs 63–67), longer tail (155–161 vs 80–115 µm), smaller c ratio (4.2–4.5 vs 5.0–6.2), and higher cʹ ratio (14–16 vs 9–11).

Remarks. The presently described new species was recovered from an agricultural wheat field usually plowed annually. Detailed SEM studies helped establish its generic identity, but further samplings to get fresh material for molecular phylogenetic studies failed. It has a unique head morphology, however, not reported or illustrated to date for any members of Tylenchidae . Light microscope observations at first indicated the presence of an anterior disk, also confirmed in SEM studies, and all other morphological characters (especially longitudinal amphidial slits) supported its placement under the genus Discotylenchus . Future molecular studies will help determine the phylogenetic affinities of this species.

Figures

FIGURE 1. Discotylenchus biannulatus n. sp. Female. A&B: Pharyngeal region; C: Lip region; D: Entire body; E: Reproductive system; F&G: Tail; H: Lateralfield at mid-body.

FIGURE 2. Light microphotographs of Discotylenchus biannulatus n. sp. Female. A: Pharyngeal region; B: Reproductive system; C&D: Lip region; E: Corpus region; F: Tail terminus; G: Lateral field at mid-body. (Scale bars = 10 µm).

FIGURE 3. Scanning electronic microscopy of Discotylenchus biannulatus n. sp. A: Lip region; B: En face view of lip region showing perioral disc; C: Lip region showing longitudinal amphidial aperture and head annuli; D&E: Details of anterior end showing head shape and body annuli; F: Four incisures in lateral field at mid-body; G: Lateral view of anus region; H: Lateral view of vulva. (Scale bars: A–C = 0.5 µm; D, G = 2 µm; E = 5 µm; F, H = 1 µm).