Tylencholaimellus persicus, Adeldoost, Yaser, Heydari, Ramin & Pedram, Majid, 2015

Adeldoost, Yaser, Heydari, Ramin & Pedram, Majid, 2015, Morphological and molecular characterization of Tylencholaimellus persicus sp. n. (Dorylaimida: Tylencholaimellidae) from Iran, Zootaxa 4040 (1) : -

Tylencholaimellus persicus sp. n.

Figs 1 & 2

Measurements. Table 1.

Description. Female. Slender nematodes of medium size, slightly curved ventrally upon fixation, tapering gradually towards anterior end. Cuticle dorylaimoid, two layered, outer layer bearing distinct transverse striations. Lateral chord one fourth to one third of mid-body width. Lip region expanded, separated from body contour by a sharp constriction, forming a large disk-like structure, 5.5–6.0 Μm wide or ca. 3 times wider than high. Amphidial fovea cup-shaped, its opening a transverse slit ca. one lip region width from anterior end. Odontostyle typical of the genus, ca. 1.8 times longer than odontophore, provided with dorsal stiffening piece covering entire dorsal arm, its aperture one-sixth of odontostyle length. Odontophore with basal knobs. Guiding ring at anterior half of odontostyle while resting. Pharynx composed of the anterior narrow and slender part connecting to the small pharyngeal bulb occupying ca. 20% of the pharynx, its nuclei not clearly seen. Cardia hemispherical, 5.5–6.5 Μm long and 3.5–4.5 Μm wide. Nerve ring at 60–62% of the neck length. Intestine coarsely granular. Prerectum 2.2 times, and rectum 0.9–1.2 times anal body diameter long, respectively. Reproductive system mono-opisthodelphic. Anterior genital branch reduced to an AUS, in length, occupying 7–8% of body length and containing sperm. Posterior branch normal, poorly developed compared to reproductive system of some other dorylaim taxa (especially in the lack of a visible sphincter), 150–241 Μm long or 24.4–27.1% of body length, composed of a tubular uterus 70–73 µm long, a 60–65 µm long oviduct swollen in proximal end and forming a less developed pars dilatata oviductus, containing sperm in almost all examined individuals, and a reflexed ovary, 79–102 Μm long. Sphincter not visible (and maybe undeveloped). Usually a maturing oocyte 40–60 µm long in size was observed in distal end of the ovary. Vagina perpendicular to body axis, occupying less than half (40%) of the corresponding body diameter, composed of pars proximalis vaginae (10–12 Μm long), short (1.5–2.0 Μm long), slightly curved pars distalis vaginae, and pars refringens vaginae apparently absent. Vulva a transverse slit. Tail broadly rounded with two caudal pores on each lateral side.

TABLE I. Morphometrics of Tylencholaimellus persicus sp. n. from Iran, in Μm and in the form average ± SD (range).

Male. General morphology similar to that of female, except in characters related to the reproductive system. Testes paired, opposed and spermatozoa spindle-shaped, 5.5–6.0Μm long and 1 Μm wide. In addition to an adanal pair, there is only one ventromedian supplement outside the spicule range at a distance of 30 µm anterior to cloacal opening. Spicules moderately sclerotised, dorsal contour irregularly convex, 5.0–5.2 times longer than width at wider part in proximal half, ventral contour with shallow hump, but distinct hollow, capitulum small, not offset, 2– 3 µm long and distal tip ca. 1.5 µm wide. Tail dorsally convex with broadly rounded terminus.

Diagnosis and relationships. Tylencholaimellus persicus sp. n. is characterized by its 613–885 Μm long body, expanded lip region, separated from body contour by a sharp constriction, forming a large disk-like structure, odontostyle and odontophore respectively 12–14 and 6.5–8.0 Μm long, female genital system mono-opisthodelphic with relatively long AUS, 50–80 Μm long, V index of 36.5–41.5, broadly rounded tail, abundant males in population with spicules 22–25 Μm long and one ventromedian copulatory supplement. The new species is compared with five known species of the genus having perioral disc, rounded tail and AUS namely T. coronatus Thorne, 1939 , T. incertus Colomba & Vinciguerra, 1979 , T. montanus Thorne, 1939 , T. ozarkensis Goseco, Ferris, & Ferris, 1975 and T. projectus Siddiqi, 1964 . Compared to these taxa, the new species has an expanded lip region separated from body contour by a sharp constriction, forming a large disk-like structure. Detailed comparisons with the above-mentioned species are discussed below.

The new species differs from T. coronatus (data from Andrássy, 2009) by its shorter odontostyle (12–14 vs 16– 18 µm), posteriorly located vulva (V = 36.5–41.5 vs 30–36), smaller c´ ratio (1.1–1.3 vs 1.4–1.6), males with one (vs two) ventromedian supplement and broadly rounded tail end (vs conical, rounded terminus).

Compared to T. incertus (probably the closest species, disregarding lip region morphology), the new species differs by its AUS not reaching the pharyngeal bulb and larger c´ [1.1–1.3 vs 0.83 (calculated from drawing)].

In comparison with T. montanus (lectotype and paralectotypes from Goseco et al., 1975), the new species basically differs by its longer odontostyle (12–14 vs 9.6 µm), longer AUS (50–80 vs 6.4 µm) and broadly rounded vs bluntly conoid tail end.

Compared to T. ozarkensis , another closely related species, the new species has a slightly longer odontostyle (12–14 vs 11 µm in holotype) and males with one ventromedian supplement (vs lacking).

The new species differs from T. projectus (data from Goseco et al., 1975), by its longer basal bulb (30–39 µm vs 28–32 µm), more posteriorly located vulva (V = 36.5–41.5 vs 32–35) and broadly rounded tail end (vs conoid, rounded end).

Furthermore, the new species is close in morphology to one species of the genus Margollus Peña-Santiago, Peralta & Siddiqi, 1993 : M. bokanicus Pachideh, Niknam, Jabbari & Peña-Santiago, 2015 (although examined individuals of the new species lack the typical labial and postlabial sclerotization characteristic of the genus Margollus ). These two taxa can be separated on the basis of the following characters: T. persicu s has an expanded lip region, separated from the rest of the body by a constriction, forming a large disk-like structure vs lip region more or less expanded (only one individual with expanded lip region was found in the type population of M. bokanicus ); longer AUS (50–80 vs 26–29 µm), differences in position of vulva (V = 36.5–41.5 vs 40–47) and the presence of functional males in population vs lacking for M. bokanicus .

Figures

FIGURE 1. Tylencholaimellus persicus sp. n. A: Neck region; B: Male posterior body region; C: Female reproductive system; D: Details of anterior end; E: Female posterior body region.

FIGURE 2. Tylencholaimellus persicus sp. n. A – D: Details of anterior end, showing stylet and labial disc (A, B), guiding ring (C) and amphidial pouch (D); E: Surface of cuticle; F: Part of female less developed reproductive system and sperm inside it; G: Part of female less developed reproductive system showing AUS; H: Vagina in detail; I: Female tail; J: Male posterior body region. All scale bars = 10 µm.