Talanema ngiguae, Mejía-Madrid & Peña-Santiago, 2025

Talanema ngiguae sp. nov.

( Figs 1 View FIGURE 1 & 2 View FIGURE 2 )

Material examined: Three females and two males, in acceptable or good state of preservation.

Morphometrics: See Table 1.

Description: Adult. Moderately slender ( a = 20–28) nematodes of medium size, 1.24–1.63 mm long. Body cylindrical, tapering towards both ends. Upon fixation, habitus slightly curved ventrad, to an open C shape in females and J-shaped in males. Cuticle almost smooth under light microscope, three-layered, especially distinguishable at caudal region, consisting of thin outer and inner layers and a much thicker intermediate layer, its total thickness 2.5–3 µm at anterior region, 2.5–4 µm in mid-body, and 4–7.5 µm on dorsal side of tail. Lateral chord 13–15 µm or 21–25% of maximum body diameter. Lip region truncate, hardly offset by a weak depression, 3.0–3.3 times as wide as high and less than one-third (27–30%) of body diameter at neck base; lips moderately amalgamated and hardly angular, their perioral area differentiated into small but appreciable liplets. Amphid fovea funnel-like, 7–8 µm wide, its aperture occupying ca one-half (47–53%) of lip region diameter. Cheilostom a truncate cone with rather thick walls. Odontostyle robust, visibly sigmoid, 4.8–5.6 times as long as wide, somewhat longer (1.2–1.3 times) than lip region diameter, aperture 9–9.5 µm or ca one-half (48–50%) of the total length. Guiding ring double, fixed ring situated at 9–10.5 µm or 0.6–0.7 times the lip region diameter from the anterior end. Odontophore rod-like, 1.4–1.6 times longer than odontostyle. Pharynx entirely muscular, gradually enlarging into the basal expansion that is 4.9–5.8 times longer than wide, 2.8–3.1 times longer than body diameter at neck base, and occupies less than one-half (45–46%) of the total neck length, gland nuclei located as follows: DO = 55–57, DN = 57–60, S 1 N 1 = 65–70, S 1 N 2 = 72–76, S 2 N = 84–86. Nerve ring located at 119–141 µm or 35–41% of the total neck length from the anterior end. Pharyngo-intestinal junction consisting of a rounded conoid cardia enveloped by intestinal tissue, all together forming a tongue-like structure, 21–36 x 13–18 µm, bulging into the intestinal lumen.

Female. Genital system diovarian, with equally developed branches, the anterior 193–261 µm long or 16–18% of body length, the posterior 203–260 µm or 15–17% of body length. Ovaries often large, reaching and surpassing the sphincter level, 104–190 µm the anterior and 97–190 µm the posterior, with oocytes first arranged in two or more rows, then in a single row. Oviduct subterminally joining the ovary, 64–86 µm or 1.1–1.5 times the body diameter long, consisting of a slender distal region made of prismatic cells and often a well-developed proximal pars dilatata with visible lumen and sometimes a few sperm cells inside. Sphincter present between oviduct and uterus. Uterus tripartite, usually convoluted, 153–190 µm long or 2.7–2.8 body diameters, consisting of a distal, almost spherical, pars dilatata with visible lumen, a long and slender intermediate section without visible lumen and somewhat refractive lining, and a proximal dilate region with wide lumen. Uterine eggs not observed. Vagina extending inwards 26–31 µm, up to one-half (45–50%) of body diameter: pars proximalis 18–21 x 11–14 µm, with walls slightly sigmoid and surrounded by weakly developed musculature, pars refringens consisting of (lateral view) two trapezoidal or drop-shaped, sclerotized, separate pieces measuring 3–5 x 3.5–5.5 µm with a combined width of 11–16 µm, and pars distalis 2–3.5 µm long. Vulva a post-equatorial, longitudinal slit. Prerectum 1.8–2.9, rectum 1.4–1.6 anal body diameters long. Caudal region conical with finely rounded terminus, ventrally straight to somewhat convex, dorsally first convex, then with a more or less (usually well) distinct concavity, giving a digitate aspect to the tail; inner core reaching 69–74% of tail length, leaving a relatively short hyaline portion.

Male. Prerectum 3.9–4.0, cloaca 1.7–1.9 times the body diameter at level of cloacal opening. Genital system diorchic, with opposite testes. In addition to the ad-cloacal pair, situated at 10–11µm from the cloacal aperture, there is a series of 14–17, almost contiguous, 7.5–10 µm apart, ventromedian supplements, the most posterior of them at 41–53 µm from the ad-cloacal pair, at level of anterior end of the spicules or a short distance in front of it, then with an appreciable hiatus. Spicules dorylaimid, 5.7–5.8 times as long as wide, 2.0–2.1 times the body diameter at level of the cloacal aperture: head 17–19 µm long or 25–28% of spicule length, 2.3–2.7 times longer than wide, and its dorsal side much longer than the ventral one; median piece occupying 33–38% of spicule maximum width; posterior tip 3.5–4.5 µm wide; ventral hump located at 25–28 µm or 36–41% of spicule length from its anterior end; curvature 130º. Lateral guiding piece 11–12 µm long, coarse, 2.7–2.8 times as long as wide, with slightly bifid end. Caudal region short, rounded conoid, ventrally somewhat more straight, dorsally more convex, lacking any concavity.

Diagnosis: The new species is characterized by its 1.24–1.63 mm long body, lip region hardly offset by depression and 14.5–16.5 µm wide with perioral liplets, odontostyle 18.5–22 µm long, guiding ring double, neck 323–383 µm long, pharyngeal expansion occupying 45–46% of the total neck length, uterus tripartite and 153–190 µm long or 2.7–2.8 body diameters, vulva longitudinal ( V = 57–61), female tail conical with a dorsal concavity (27–32 µm, c = 46–49, c’ = 0.9–1.0), male tail short and rounded conoid (23 µm, c = 67–71, c’ = 0.7), spicules 68–69 µm long, and 14–17 shortly spaced ventromedian supplements ending at level of the anterior end of spicules, with hiatus.

Separation from its relatives. In having medium-sized body (ranging between 1.0 and 2.0 mm long) and odontostyle (up to 27 µm long), lacking cuticle irregularities at the perivulval area, showing a posterior vulva ( V = 57–62) and sexual dimorphism of tail shape, the new taxon resembles the type species of the genus, T. mauritiense ( Williams, 1959) Andrássy, 1992 , from which it can be easily distinguishable (see remarks below) by its lip region hardly offset by depression ( vs weak but appreciable constriction), longitudinal ( vs transverse) vulva, longer female tail inner core (69–74 vs 42–67% of tail length), and longer spicules (68–69 vs 50–56 µm).

The new species also resembles T. baqrii ( Khan, Jairajpuri & Ahmad, 1989) Imran, Abolafia & Ahmad, 2021 (= Labronema baqri Khan, Jairajpuri & Ahmad, 1989 ) and T. digitatum ( Sukul, Das & Mitra, 1975) Andrássy, 1992 (= Labronema digitatum Sukul, Das & Mitra, 1975 ), but it can be easily distinguished from these in its almost continuous lip region ( vs offset by constriction), longitudinal ( vs transverse) and more posterior vulva ( V = 57–61 vs V = 48–56) vulva, longer spicules (68–69 vs 50–58 µm) and less ventromedian supplements (14–17 vs 19–27).

Type locality and habitat: Mexico, State of Puebla, Zapotitlán de las Salinas , Botanical Garden ‘ Helia Bravo Hollis’ at the Biosphere Reserve of Tehuacán-Cuicatlán (coordinates: 18º19.751’ N 097º27.312’ W, 18º19.785’ N, 097º27.318’ W, 18º19.759’ N 097º27.332’ W, altitude 1420 m a.s.l.), in soil crusts beneath Cericidium praecox and Prosopis laevigata . Collected on October 12, 2015 GoogleMaps .

Type material: Female holotype, two female and two male paratypes deposited at nematode collection of the University of Jaén , Spain .

Etymology: The species name ngiguae is derived from ngigua, a term that refers to the language and native people that inhabit the area of Tehuacán, Zapotitlán-Cuicatlán where this nematode was found, meaning “those who speak the tongue” as a vindication of their cultural history.

Remarks: The new taxon is described on the basis of a low number of specimens of both sexes, but enough to characterize it and to distinguish it from the closest relatives, especially with T. mauritiense (see above). For comparative purposes, Williams’ (1959) original description of latter species as well data provided by Thorne (1974) were taken into account as the true identity of its other records ( Loof, 1964; Ahmad & Jairajpuri, 1982; Botha & Heyns, 1990; De Bruin & Heyns, 1992; Mushtaq & Ahmad, 2007; Erum & Shahina, 2010) are questionable for different reasons, a matter that requires much further research and that will be addressed in a separate contribution as the present research is an ongoing programme aimed at recovering dorylaimid species from semi-desertic zones in the Neotropical region.

The description of several new species of the genus throughout the last years suggests that the diversity of Talanema is higher than initially (originally) conceived, mainly affecting several key morphological traits: lip region (offset and continuous), odontostyle, uterus complexity, vulva orientation (transverse or longitudinal), sexual dimorphism of tail shape, and number and arrangement of ventromedian supplements. The analysis of these variations requires further research, preferably supported by molecular data, a question that exceeds the aims of this contribution.