Mononchus oblongus, Andrássy, 2011

Andrássy, István, 2011, Three new species of the genus Mononchus (Nematoda: Mononchida), and the “ real ” Mononchus truncatus Bastian, 1865, Journal of Natural History 45 (5 - 6), pp. 303-326 : 309-313

Mononchus oblongus sp. nov.

( Figures 4A–F and 5A–F )

Holotype female: L = 1.72 mm; a = 29; b = 3.7; c = 6.2; c’ = 9.0; V = 54 %. Paratype females (n = 5): L = 1.60–1.88 mm; a = 25–28; b = 3.5–3.7; c = 6.0–7.1; c’ = 7.5–8.8; V = 52–54%.

General characters

Body medium long, on average 1.72 mm, 39–42 µm wide at posterior end of buccal cavity, 60–65 µm wide at cardial region, 60–68 µm wide at mid-body region and 30–36 µm wide at posterior anal lip. Habitus almost straight upon fixation. Cuticle smooth, its thickness more or less uniform, 2 µm, but thicker on tail, 3.0–3.5 µm. Labial region practically not offset, 22–23 µm wide at level of lateral lips. Lips amalgamated. Body at proximal end of pharynx 2.7–2.9 times as wide as labial region. Oral field slightly protruded, about 3 µm high. Amphids small, caliciform, their aperture located somewhat posterior to beginning of buccal capsule.

Distance between the oral field and beginning of buccal capsule 7–9 µm. Buccal capsule oblong, 48–51 µm long, 18–19 µm wide at anterior third and 17–18 µm wide at posterior third, 2.6–2.8 / 2.8–3.1 times as long as wide at anterior or posterior third, respectively. It is 2.1–2.3 times as long as labial diameter, and occupies 10.0–10.8% of entire length of neck region (from oral field to cardia). Buccal walls about 1.5 µm thick, but 2.5 µm thick just posterior to dorsal tooth, at its thickest point. Dorsal tooth 5–6 µm long from base to apex, its apex situated 10.0–11.5 µm from beginning of buccal capsule or at 21–23% of buccal length. Distance between tooth apex and opposite stomatal wall 11–12 µm. Subventral transversal ridges very thin, lying at level of tooth apex. Pharynx 450–504 µm long, cylindrical and strongly muscular. Pharyngeal collar surrounding the posterior 20–25% of stoma. Nerve ring situated at 24–27% of pharynx. Cardia simple. Rectum nearly one anal body width long.

Female

Reproductive system amphidelphic with reflexed ovaries. Genital branches short, each 2.2–2.7 body widths long or occupying 7.6–9.4% of body length. Uterus separated from the oviduct by a sphincter. Vulva a transverse slit with sclerotized, drop-shaped inner lips. Vagina 18–21 µm long, nearly as long as one-third body diameter. Mature eggs not observed. Distance between posterior end of pharynx and vulva almost as long as pharynx. Vulva–anus distance equal to 1.8–2.4 tail lengths. Tail 264– 276 µm (on average 270 µm) long, occupying 14.0–16.8% of entire length of body; first quickly then slowly tapered, in posterior third cylindrical and 4–5 µm thick. Caudal glands rather small. Tip of tail rounded with a terminal spinneret and two ventral / subventral papillae, which are setiform, 2–3 µm long, longer than in other species of the genus.

Male

Not found.

Diagnosis and relationships

The most striking morphological features of this new species are the shape and length of the buccal cavity, which is more elongate than in other congeners of similar body size, and the seta-like subterminal papillae on the tail. This new species is further characterized by an average body length of 1.72 mm, a fairly robust shape, relatively anterior position of the dorsal tooth apex at 21–23%, short gonads, sclerotized vulva, and by the medium-size, on average 8.2 anal body widths long tail.

Cobb (1917) described a new species under the name Mononchus megalaimus Cobb, 1917 from Wisconsin, USA, which was later synonymized with M. truncatus . Although Cobb gave a brief description, he illustrated the buccal region well. The buccal capsule is elongated, oblong, about 43 µm long, 1.8–1.9 times as long as the lip region width. Mononchus oblongus differs from it in having a longer buccal cavity (48–51 vs 43 µm, 2.1–2.3 vs 1.8–1.9 lip region width), longer tail (264–276 vs 210 µm), and in having long, setose caudal papillae (vs “very small”).

Nakazawa (1999) studied several specimens of M. truncatus from paddy fields in Japan. He illustrated the buccal region of one population as very similar to that of the present new species. Unfortunately, he gave no description of this form. All that is known is that the buccal capsule is about 50 µm long, and the tooth apex is located at 24%.

By virtue of the characteristic shape of the buccal cavity, M. oblongus sp. nov. comes close to M. himalayensis Rawat and Ahmad, 2000 . It can be differentiated from the latter by the more elongate buccal cavity (2.1–2.3 vs 1.6–1.8 labial widths long), the position of the dorsal tooth apex (21–23 vs 25–31%), the lack of a prevulval papilla, the conspicuously thinner tail (4–5 vs 10 µm thick at its posterior cylindrical section), as well as by the setose subterminal caudal papillae.

As for the terminal caudal papillae, the observation of Zullini et al. (2002) should still be mentioned. They found in M. truncatus Bastian, 1865 from Costa Rica that “The tail bears two small projections more similar to setae than to papillae.” Because of the lack of illustrations it cannot be decided whether those specimens belonged to M. truncatus or to another (perhaps new) species. Yet it seems certain that the Central American nematodes were not conspecific with M. oblongus sp. nov. because of their shorter buccal cavity (39–43 vs 48–51 µm; 1.6–1.7 vs 2.1–2.3 labial diameters long), more posteriorly located tooth apex (24–30 vs 21–23%) and shorter tail (185–234 vs 264–276 µm).

Type specimens

Holotype female on slide no. 14782. Paratypes: five females and two juveniles; deposited in the nematode collection of the Department of Systematic Zoology and Ecology of the Eötvös Loránd University , Budapest .

Type habitat and locality

Liver mosses from the soil near the village Ossès (Basque: Ortzaize) in the Pyrénées- Atlantiques département, southwestern France, near the French–Spanish border, about 200 m above sea level. Collected in June 1997 by K. Dózsa-Farkas (Budapest).

Etymology

The species epithet oblongus (Latin) means elongate or oblong referring to the shape of the buccal cavity, which is more elongated than usual.

Figures

Figure 4. Mononchus oblongus sp. nov. (A) Anterior end; (B) cardial region; (C) vulval region; (D, E) female posterior end; (F) tail tip. Scale bars 20 µm.

Figure 5. Mononchus oblongus sp. nov. (A–C) Anterior end; (D) cardial region; (E) vulval region; (F–H) female posterior region; (I) tail end with setiform papillae.