Morphological and Molecular Characterization of Talanema eshtiaghii sp. n. (Dorylaimida, Qudsianematidae) from Iran

Moderately slender to slender (a = 27–32) nematodes of medium size, 1.45–1.68 mm long. Body cylindrical, tapering towards both ends, but more so posteriorly, as the tail is conical in both sexes. Upon fixation, habitus slightly curved ventrad, to an open C shape. Cuticle almost smooth under light microscopy, two-layered, its total thickness 1.5–2.0 μm at anterior region, 2.5–4.0 μm in mid-body, and 4.0–4.5 μm on dorsal side of tail. Lateral chord 10.5–14.5 μm or 21–24% of maximum body diameter. Lip region offset by a weak but distinct constriction, 2.5–3.2 times as wide as high and less than one-third (24–32%) of body diameter at neck base; lips moderately separate and slightly angular, and perioral liplets might be present, labial and cephalic papillae visibly protruding. Amphidial fovea cup-shaped, its aperture 7.5–9.0 μm long or up to two-thirds (57–67%) of lip region diameter. Cheilostom a truncate, thick-walled cone. Odontostyle robust, hardly but appreciably shorter at its ventral side, 6.4–7.4 times as long as wide, longer (1.1–1.2 times) than lip region diameter, its aperture 5.5–7.0 μm or one-third to two-fifths (32–41%) of the total length. Guiding ring double, fixed ring situated at 9–11 μm or 0.7 times the lip region diameter from the anterior end. Odontophore rod-like, 1.3–1.6 times longer than odontostyle. Pharynx entirely muscular, gradually enlarging into the basal expansion that is 5.9–6.9 times longer than wide, 2.6–3.2 times longer than body diameter at neck base, and occupies less than one-half (39–43%) of the total neck length; gland nuclei located as follows: DO=59–60, DN=62–68, S₁N₁=70–75, S₁N₂=77–79, S₂N=85–87. Nerve ring located at 126–146 μm distance from anterior end or 34–43% of the total neck length. Pharyngo-intestinal junction consisting of a short and rounded conoid cardia enveloped by intestinal tissue, all together forming a longer conoid, 14–19 × 12–15 μm structure, bulging into the intestinal lumen.

Genital system diorchic, with opposite testes. In addition to the ad-cloacal pair, situated at 7.5 μm from the cloacal aperture, there is a series of 14–18, almost contiguous or shortly spaced, 6.0–7.5 μm apart, ventromedian supplements, the most posterior of them situated at 49–51 μm from the ad-cloacal pair, appreciably in front of the anterior end of spicules, then with a distinct hiatus. Spicules dorylaimid, 4.9–5.5 times as long as wide, 1.5–1.8 times the body diameter at level of the cloacal aperture: head 10.0–16.5 μm long or 18–32% of spicule length, 2.2–2.4 times longer than wide, and its dorsal side much longer and more curved than the ventral one; median piece comparatively slender, occupying 25–28% of spicule maximum width; posterior tip 3.5 μm wide; ventral hump located at 18–22 μm or 36–42% of spicule length from its anterior end; curvature 134º. Lateral guiding piece 13–14 μm long, coarse, 3.4–4.4 times as long as wide, conspicuously tapering at its posterior third. Prerectum 1.8–3.7, cloaca 1.8–1.9 body diameters long. Caudal region basically similar to that of female, but more straight or even slightly curved ventrad at the end.

Sequencing the D2–D3 region of the 28S rDNA resulted in one sequence 751 bp (OP870361) long. The BLAST homology search showed it has an 89.09% identity with Talanema baqrii (Khan et al., 1989; Imran et al., 2021) (MT645228), 91% identity with T. ibericum (Peña-Santiago et al., 2022) (OP793646) and 94% identity with Talanema sp. (OP870362).

The new species is characterized by its 1.45–1.68 mm long body, lip region offset by constriction and 13–15 μm wide, odontostyle 15–18 μm long, guiding ring double, neck 312–362 μm long, pharyngeal expansion occupying 41–43% of the total neck length, uterus tripartite and 111–189 μm long or 2.1–3.2 body diameters, vulva transverse (V = 55–58), tail similar in both sexes, conical with a dorsal concavity (30–44 μm, c = 33–56, c’ = 1.0–1.6), spicules 49–56 μm long, and 14–18 shortly spaced ventromedian supplements in front of the level of the anterior end of spicules, with distinct hiatus.

Morphologically and morphometrically, the new species resembles three Talanema species showing no sexual dimorphism of tail shape, namely, T. ibarakiense (Khan and Araki, 2002; Andrássy, 2011), T. pararapax (Ahmad and Jairajpuri, 1982; Andrássy, 1991) and T. sphinctum (Mohilal and Dhanachand, 2001; Imran et al., 2021), but it can be distinguished from these in its shorter odontostyle (15–18 versus 20 μm long or more). Besides, it differs from T. ibarakiense in its larger general size (body length 1.45–1.68 versus 1.0–1.2 mm), more posterior vulva (V = 55–58 versus 50–52), longer tail (30–44 versus 21–24 μm, c’ = 1.0–1.6 versus 0.8–0.9), and less (14–18 versus 21–22) ventromedian supplements with distinct (versus without) hiatus. From T. pararapax in its shorter spicules (49–56 versus 57–63 μm) and different arrangement of ventromedian supplements (ending in front of versus at level of the anterior end of spicules). It can be separated from the type population of T. sphinctum in its more posterior vulva (V = 55–58 versus V = 52–55), higher number of ventromedian supplements (14–18 versus 8) with very different arrangement (shortly versus widely spaced, with distinct versus no hiatus). It is also similar to T. saccatum (Jabbari et al., 2021), an Iranian monosexual species, from which the new species can be separated in its more slender body (a = 27–32 versus a = 22–26), somewhat shorter odontostyle (15–18 versus 18–20 μm), and slightly longer female tail (30–44 versus 24–31 μm, c’ = 1.0–1.6 versus c’ = 0.8–1.0) with no (versus abundant) saccate bodies. Finally, the new species also resembles Labronema digiturum (Vinciguerra, 1984), a taxon with a questionable belonging to Labronema, but it can be distinguished from this in its much more slender body (a = 27–32 versus a = 16–20), shorter odontostyle (15–18 versus 19–20 μm), tripartite (versus apparently simple) uterus, absence (versus presence) of cuticular irregularities (wrinkles) at both sides of vulva, and shorter spicules (49–56 versus 67 μm).

The evolutionary relationships of the new species, as derived from the molecular analyses, are presented in the tree of Figure 3. The 28S rDNA sequence of T. eshtiaghii sp. n. formed a maximally supported clade (1.00 Bayesian posterior probability) with other Talanema representatives, namely T. baqrii, T. ibericum and Talanema sp. This means that, at present, Talanema is a monophyletic taxon. Nevertheless, its external relationships remain unsatisfactorily resolved. Thus, on the one hand, it forms part of a larger clade also including two sequences of Labronema montanum (Peña-Santiago and Abolafia, 2019) as a sister group, but with comparatively low support (0.84 BPP). On the other hand, this (Talanema + Labronema) clade is only one out of six Dorylaimina subclades, whose evolutionary relationships are neither well resolved.

Figure 3:

Northwestern Iran, East Azarbaijan province, Sufiyan district, Roodghat area, Zeinabad village (38°17′46″N, 46°07′37″E, elevation 1528 m a.s.l.), where the new species was collected in soil from the rhizosphere of common wheat (Triticum aestivum L.).

Female holotype, three female paratypes and two male paratypes deposited with Collection of Nematology Laboratory, University of Tabriz, Iran. One female paratype and one male paratype deposited in the Nematode Collection of the University of Jaén, Spain.

The LSID for this publication is urn:lsid:zoobank.org:act:250EA066-7CC1-48DD-94C5-4ADD6490E015

The new species is named in honor of Dr. Hassan Eshtiaghi, the late Nematologist in the Department of Plant Protection, University of Tehran, Tehran, Iran.