Doryllium asymmetricum, Ahmad & Ahad & Islam & Sturhan, 2018

Ahmad, Wasim, Ahad, Sumaya, Islam, Md. Niraul & Sturhan, Dieter, 2018, Taxonomy of the genus Doryllium Cobb, 1920 (Nematoda: Dorylaimida) with description of two new and a known species, Zootaxa 4441 (2), pp. 261-278 : 271-275

Doryllium asymmetricum sp. n.

( Figs. 6 & 7 )

Material examined. Eight females and five males in good state of preservation.

Description. Measurements, see Table3

Female: Small sized nematodes, slightly curved ventrad upon fixation; body cylindrical tapering slightly towards the extremities. Cuticle with two distinct layers, 3–4 µm thick at midbody and 5–6 µm on tail. Outer cuticle finely striated; inner layer thick in tail region. Lateral chords occupying about one-fourth to one-third of the midbody diameter. Ventral and lateral body pores indistinct. A dorsal body pore slightly posterior to nerve ring visible in a few specimens. Lip region slightly offset, 1.7–2.0 times as wide as high or about one-third of body diameter at neck base; lips rounded and amalgamated; labial papillae barely raised. Amphids cup-shaped, aperture occupying about one-half of lip region diameter. Stoma a truncate cone. Odontostyle asymmetrical, about as long as lip region diameter, with distinct lumen and aperture. Odontophore slightly flanged, 1.6–1.8 times the odontostyle length. Guiding ring simple, refractive, located 0.6 times lip region diameter from anterior end. Pharynx consists of a slender and weakly muscular anterior part, expanding gradually into a pear-shaped basal bulb, occupying about 16–18% of total neck length. Cardia rounded-conoid, about one-third corresponding body diameter long. Nerve ring at 50–58% of neck length from anterior end. Genital system mono-opisthodelphic. Ovary reflexed, measuring 98–161 µm long, reaching the oviduct-uterus junction; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 116–165 µm, its proximal and distal parts not differentiated. Oviduct-uterus junction marked by weak sphincter. Uterus short and tubular, measuring 35–47 µm, filled with sperms; uterine egg, measuring 65 x 19 µm, observed in one specimen.Anterior genital branch small, 0.7–1.5 midbody diameters long, filled with sperms.Vagina cylindrical; pars proximalis vaginae 4–5 µm long, wall encircled by muscles; pars distalis vaginae short, 3 µm long with slightly curved walls; pars refringens absent. Vulva a transverse slit. Prerectum 2.2–2.5 and rectum 0.7–1.2 anal body diameters long. Tail short, rounded hemispheroid, 0.8–1.1 anal body diameters long.

Male: General morphology similar to female except for the posterior region being more ventrally curved. Sperms spindle-shaped. Only the adcloacal pair of supplements present, located at 6 µm anterior to cloacal aperture. Spicules, slender, slightly curved ventrad, 1.5 times cloacal body diameter long. Lateral guiding pieces, simple, rod-like, one-fourth of the spicules length. Tail short, rounded hemispheroid, 1.1 anal body diameter long.

Type habitat and locality. Oat field, Lintach near Amberg, Germany; collected by Dr. Dieter Sturhan on 0 7.10. 1981.GPS Coordinates 49°26′34″ N and 11°51′45″ E

Type specimens. Holotype female on slide Doryllium asymmetricum sp. n. / 1; paratypes females on slides Doryllium asymmetricum n. sp. / 2–5; paratype males on slides Doryllium asymmetricum sp. n. /6–8 deposited with the nematode collection of the Department of Zoology , Aligarh Muslim University, India . Two paratype female and males each deposited with German nematode collection.

Etymology. The new species is named D. asymmetricum sp. n. because of its asymmetrical odontostyle.

Diagnosis and relationships. Doryllium asymmetricum sp. n. is characterized by having a body length of 0.52–0.63 mm; cap-like, slightly offset lip region; asymmetrical odontostyle, 6 µm long; weakly flanged odontophore 9–11 µm long (total spear length: 16–17 µm); pharynx with slender anterior part, which expands gradually into pear-shaped basal bulb occupying about 16.4–18.5% of total neck length; mono-opisthodelphic female genital system; anterior uterine sac 17–30 µm, filled with sperms; transverse vulva and roundedhemispheroid tail.

With its unconstricted pharyngeal bulb, presence of anterior uterine sac and tail shape, the new species comes close to Doryllium jamesi ( Goseco, Ferris & Ferris, 1975) Andrássy, 2009 and Doryllium nudum Thorne, 1964 . From D. jamesi , it differs in having a slightly longer body (vs 0.45–0.50 mm); asymmetrical odontostyle (vs symmetrical); lower c ratio (vs 56–64); more anteriorly located vulva (vs 41–47%); longer anterior uterine sac (vs 6.4 µm) and longer tail (vs 7–9 µm).

From Doryllium nudum , the new species differs in having a slightly longer body (vs 0.50 mm); higher a, b and c ratios (vs 21, 3.5 and 34, respectively); vulva more anteriorly located (vs 38%); shorter odontostyle (vs 7 µm); smaller combined odontostyle and odontophore length (vs 19 µm); asymmetrical odontostyle and odontophore with weak flanges (vs odontostyle symmetrical and odontophore without flanges) and males present (vs absent).

Discussion. Both new species distinctly differ from all the known species of the genus Doryllium in their characteristic odontostyle asymmetry (vs short, tubular) and in the odontophore bearing flanges instead of round basal knobs. However, there is a very fine line of differentiation between distinct knobs and flanges and sometimes these two terms are used synonymous and this character should not be used for generic differentiation. Even though the odontostyle nature appears different, proposing a new genus on the basis of such a slight difference does not seem reasonable. Hence, for the present, both new species are placed in the genus Doryllium and the diagnosis of the genus is slightly emended to accommodate the additional variation. A diagnostic compendium (table 4) of the species of the genus Doryllium is also provided.

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Lrd = lip region diameter Ods = Odontostyle

Ph. bulb = Pharyngeal bulb Vms = # of ventromedian supplements

* = Calculated value from illustrations Geo. dist. = Geographical distribution

Figures

FIGURE 6. Dorylllium asymmetricum sp. n A. Entire female; B. Entire male; C. Anterior region; D. Anterior end showing amphid; E. Pharyngeal region; F. Pharyngeal bulb; G. Female genital system; H. Anterior uterine sac; I. Female posterior region; J. Male posterior region.

FIGURE 7. Doryllium asymmetricum sp. n. A–B. Anterior region; C. Anterior end showing amphid; D. Pharyngeal bulb; E. Female genital system; F. Vulval region; G. Egg in female uterus; H–I. Female posterior region; J. Male posterior region. (Scale bar A–F, H,J = 10 µm; G–I = 20 µm).