Five females and four males, in excellent state of preservation.

See Table 1.

Adult. Slender nematodes of medium size, 1.92–2.40 mm long. Body cylindrical, slightly tapering towards both ends. Habitus more or less curved ventrad upon fixation, adopting an open ‘C’ shape. Cuticle dorylaimoid, with very fine transverse striation, sometimes difficult to distinguish; 3.5–5.0 μm thick in anterior region, 5.5–8.0 μm at mid–body and 8–13 μm on tail. Lateral chord 10–18 μm wide at mid–body, occupying 15–30% of mid–body diameter; lateral pores readily visible, arranged in two rows along both margins of lateral chord. Lip region truncate, somewhat angular, offset by marked constriction, 3.0–4.0 times as broad as high and 25–36% of body diameter at neck base; lips moderately separated; labial and cephalic papillae protruding. Amphid fovea funnel–like, its opening occupying 10–11 μm or three–fifths (60%) of lip region diameter. Odontostyle quite robust, wider than adjacent cuticle, 4–6 times as long as wide, 1.0–1.1 times the lip region diameter and 0.8–1.1% of body length; aperture occupying less than one–third (27–30%) its length. Guiding ring simple but distinct, at 10–12 μm or 0.5–0.7 times the lip region diameter from anterior end. Odontophore rod–like, lacking any differentiation, 1.1–1.4 times the odontostyle length. Pharynx consisting of a slender but muscular anterior portion enlarging gradually; basal expansion 9–11 times as long as broad, 5.3–6.0 times longer than body diameter at neck base, and occupying more than half (54–56%) of total neck length; pharyngeal gland nuclei situated as follows: DO = 46–50%, DN = 48–53%, S₁N₁ = 72–76%, S₁N₂ = 76–81%, S₂N = 87–90%. Of note, S₁N are significantly smaller than S₂N. Nerve ring located at 155–187 μm or 32–41% of total neck length. Cardia tongue–like, 12–19 x 11–16 μm and surrounded by intestinal wall.

Female. Genital system didelphic-amphidelphic, with both branches well and equally developed, the anterior 364–476 μm long or 15–18% of total body length, and the posterior 358–395 μm long or 14–16% of total body length. Ovaries reflexed, moderately developed, sometimes reaching and surpassing the sphincter level; the anterior 114–131 μm, the posterior 101–127 μm long; oocytes arranged distally in several rows and then proximally in a single row. Oviduct joining ovary, 88–130 μm long or 1.3–1.8 body diameters and consisting of a tubular part and a moderately developed pars dilatata with small lumen. Oviduct-uterus junction marked by a distinct sphincter. Uterus 162–218 μm long or 2.3–3.5 times the corresponding body diameter, bipartite, i.e., consisting of two sections with variable length: a wider proximal region with distinct lumen containing abundant sperm cells, and a distal part with narrow lumen and globular walls surrounded by circular muscles. Vagina extending inwards 32–45 μm or less than half (36–44%) of the corresponding body diameter; pars proximalis longer than wide, 26–40 × 19–22 μm, with slightly sigmoid walls and surrounded by moderately developed musculature; pars refringens with (in lateral view) two distinct, trapezoidal, closely-spaced pieces, measuring 6–8 × 8–11 μm and with a combined width of 17–21 μm; pars distalis very short, with two small sclerotizations close to the pars refringens. Vulva a post–equatorial longitudinal slit appearing in lateral view as a short longitudinal depression. Prerectum 1.3–2.1 anal body diameters long, with a well developed blind sac. Rectum 0.9–1.3 times the anal body diameter. Tail short, conical with rounded tip to conoid, ventrally nearly straight, dorsally more convex. Two pairs of caudal pores, one subdorsal, other lateral or subventral.

Male. Genital system diorchic, with opposite testes. In addition to the adcloacal pair, situated at 22–27 μm from cloacal aperture, there is a series of 13–17 shortly and regularly spaced (11–16 μm apart) ventromedian supplements, outside the range of spicules; posterior-most ventromedian supplement located at 47–53 μm from adcloacal pair. Spicules strongly curved ventrad and moderately robust, 4.0–5.0 times as long as wide and 1.6–1.7 anal body diameter long. Lateral guiding pieces short and robust, 11–16 μm long, 2.5–4.0 times as long as wide, with bifurcate terminus in which the posterior arm is visibly longer than the anterior one. Prerectum length 1.7–2.3 times the anal body diameter. Tail somewhat more conoid than that of female.

The new species is characterized by body length of 1.92–2.40 mm , lip region offset by constriction and 17–19 μm wide, odontostyle 16–19 μm long with aperture occupying less than one-third (27–30%) its length, neck 428–690 μm long, pharyngeal expansion 369–390 μm long or occupying 54–56% of total neck length, female genital system amphidelphic, uterus bipartite and 162–218 μm long or 2.3–3.5 times as long as body diameter, pars refringens vaginae well developed, V = 54–57.5, vulva longitudinal, prerectum bearing a blind sac, tail conical with rounded tip to conoid (25–36 μm, c = 60–69, c’ = 0.5–0.9), spicules 68–72 μm long, precloacal pair of supplements well far (22–27 μm) from cloacal aperture, and 13–17 shortly spaced ventromedian supplements with hiatus.

The general pattern of this species fits well with that of the genus Crassolabium. It resembles Crassolabium diversum (Ciobanu, Popovici, Abolafia & Peña-Santiago, 2007) Peña–Santiago and Ciobanu 2008, Crassolabium major (Thorne, 1974) Peña-Santiago and Ciobanu 2008, Crassolabium montanum (Ciobanu, Popovici, Abolafia & Peña-Santiago, 2007) Peña-Santiago and Ciobanu 2008 and Crassolabium vietnamense Vu, Ciobanu, Abolafia & Peña-Santiago, 2010. It differs from Crassolabium diversum in its larger body (vs L = 1.19–1.96 mm), longer pharyngeal expansion (vs 350–410 µm long or 40–48% of total neck length), vulva longitudinal (vs transverse), longer tail (vs 18–23 µm), longer spicules (vs 46–54 µm) and higher number of ventromedian supplements (vs 4–7). From Crassolabium major in its larger body (vs L = 1.5 mm), longer odontostyle (vs 13 µm long), vulva longitudinal (vs transverse), female tail more conical (vs rounded), longer spicules (vs about 50 µm) and higher number of ventromedian supplements (vs 9). From Crassolabium montanum in its larger body (vs L = 1.56–1.90 mm), lip region offset by constriction (vs continuous or offset by depression), shorter odontostyle (vs 20–22 µm), longer and bipartite uterus (vs 1.0–1.5 times the body diameter and simple), tail lacking (vs abundant) blister–like structures, and male as frequent as female (vs absent). From Crassolabium vietnamense in its larger body (vs L = 1.55–1.88 mm), shorter odontostyle (vs 19–22 µm), uterus bipartite (vs tripartite, with a distal, spherical region), vulva longitudinal (vs transverse), longer spicules (vs 53–55 µm), higher number of ventromedian supplements (vs 8–9), and hiatus present (vs two ventromedian supplements within the range of spicules).

The new species is also comparable to Aporcelaimellus index (Thorne, 1939) Andrássy 1986, in its eneral morphology and morphometry as well as the peculiar shape of lateral guiding pieces being short, robust and with bifurcate terminus in which the posterior arm is visibly longer than the anterior one, forming digitations, hence the specific name index as stated by Thorne (1939). Aporcelaimellus index is a very atypical member of Aporcelaimellus Heyns, 1965 because the odontostyle aperture is distinctly shorter than half its total length, making its identity questionable, and indicating further studies for its elucidation. It was originally described on the base of only one male specimen from Utah (U.S.A.), and later reported, also with only one male specimen, from Mongolia by Andrássy (1964). The new species herein described differs from Aporcelaimellus index in the position of the pre-cloacal pair of male genital papillae (vs closer to cloacal aperture) and in the number (vs 25–27) and arrangement (vs contiguous) of ventromedian supplements.

Finally, in the location of the pre-cloacal pair of male genital papillae - comparatively far from cloacal aperture, indeed a very unusual feature in dorylaims -the new species is reminiscent of the genus Amblydorylaimus Andrássy, 1998, with the type and only species Amblydorylaimus isokaryon (Loof, 1975) Andrássy 1998, but it differs from this in the nature of odontostyle (vs weakly sclerotized and longer, 31–35 µm long), S₁N much smaller than DN and S₂N (vs equally sized all of them), and hiatus present (vs absent).

The soil samples were collected from Mahmood Abad region (GPS coordinates: 38°48'N, 46°51'E), Arasbaran rangelands, East Azarbaijan province, north-west Iran.

Female holotype, two female paratypes and three male paratypes are deposited in Nematode Collection, Faculty of Agriculture, University of Tabriz, Tabriz, Iran. One female paratype and one male paratype with nematode collection of Departamento de Biología Animal, Biología Vegetal y Ecología, Universidad de Jaén, Spain.

The specific epithet refers to the geographical area where the new species was collected from.