Mononchus medius, 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 : 313-317

Mononchus medius sp. nov.

( Figures 6A–E and 7A–I )

Holotype female: L = 1.43 mm; a = 36; b = 3.8; c = 6.6; c’ = 8.5; V = 51 %. Paratype females (n = 6): L = 1.41–1.82 mm; a = 32–38; b = 3.7–4.4; c = 6.6–8.1; c’ = 7.7–8.0; V = 50–52%.

General characters

Body medium length, 1.4–1.8 mm, moderately slender, 30–33 µm wide at posterior end of stoma, 40–43 µm wide at cardial region, 40–48 µm wide in the middle and 25–28 µm wide at posterior anal lip; slightly ventrally curved after fixation. Cuticle smooth and thin, 1.2–1.6 µm thick on most of body, and 2.5–3.5 µm thick on the middle of tail. Labial region practically continuous with adjacent body, 20–21 µm wide, lips poorly developed. Oral field slightly protruded, 1.5–2.0 µm high. Body at posterior end of pharynx 2.0–2.3 times as wide as labial region. Amphids small, their aperture located halfway between the beginning of buccal capsule and the dorsal tooth apex.

Distance between the oral field and beginning of buccal capsule 7–8 µm. Buccal capsule 35–37 µm long and 15–17 µm wide at anterior third or 14–15 µm wide at posterior third, 2.2–2.3 times as long as wide, or 1.6–1.8 times as long as labial diameter, occupying 8.9–9.6% of entire length of neck (from oral field to cardia). Buccal wall mostly 1.5 µm thick, just posterior to tooth 2.5 µm thick. Dorsal tooth strong, 4 µm long from base to apex, its apex located 12–13 µm from anterior end of buccal capsule or at 31–34% of buccal length. Distance between tooth apex and opposite stomatal wall 9–10 µm. Subventral transversal ridges lying anterior to tooth apex. Pharynx 375–415 µm long, nearly cylindrical and heavily muscular. Pharyngeal musculature surrounding 30–34% of buccal capsule. Nerve ring situated at anterior third of the total neck length. Cardia short, conical. Rectum nearly as long as anal body diameter. Female

Genital system amphidelphic. Each genital branch 3.2–4.6 times as long as body width, or occupying 8.8–12.0% of body length. Ovaries reflexed near vulva. Sphincter between uterus and oviduct present. Vulva a transverse slit with sclerotized, dropshaped inner lips. Vagina 18–20 µm long, occupying 30–35% of corresponding body diameter. Uterine eggs one at a time, 80–86 by 26–30 µm, twice the body width long. Distance between posterior end of pharynx and vulva as long as or somewhat (1.2–1.3 times) longer than pharynx. Vulva–anus distance equal to 2.2–2.9 tail lengths. Tail 205–225 µm (on the average 215 µm) long, occupying 12–15% of total body length, tapering to cylindrical shape in posterior third; its cylindrical part (posterior third) 5–7 µm wide, rounded on tip, and straight or ventrally curved. Caudal glands well developed, spinneret terminal. Tail tip with two minute subventral papillae.

Male

Not found.

Diagnosis and relationships

A medium-sized Mononchus species characterized by an average body length of 1.55 mm, thin cuticle, labial region not offset, 20–21 µm wide, large buccal cavity of 35–37 by 15–17 µm, posterior location of dorsal tooth apex at 31–34%, subventral ribs anterior to tooth apex, vulval lips sclerotized, and by the tail on average 7.7 anal body widths long and cylindrical in its posterior part.

By virtue of the body length, size of the buccal cavity and the length of the tail, M. medius sp. nov. comes close to the species M. truncatus Bastian, 1865 , M. aquaticus Coetzee, 1968 and M. pulcher Andrássy, 1993 . It differs from M. truncatus (as characterized herein) in having a narrower labial region (20–21 vs 24–28 µm wide), smaller buccal cavity (35–37 vs 42–50 µm) and a more slender cylindrical part of the tail (5–7 vs 10–12 µm thick). It differs from M. aquaticus by the longer buccal cavity (35–37 vs 26–32 µm), more posterior position of dorsal tooth apex (31–34 vs 20–25%), subventral ribs lying anterior (vs posterior) to the tooth apex, longer and more slender tail (215 vs 150 µm on the average, or 7.7–8.5 vs 4–6 anal body widths long), and by the thinner cylindrical part of the tail (5–7 vs 12–14 µm). Finally, it differs from M. pulcher by the more posterior position of the dorsal tooth apex (31–34 vs 20–22%), subventral transverse ribs lying anterior to the tooth apex (vs posterior), and by the longer and more slender tail (7.7–8.5 vs 6–7 anal body widths long, and 5–7 vs 9–11 µm thick at posterior third).

Rawat and Ahmad (2000) gave a short description and some drawings of M. truncatus from Garhwal Himalayas, India. Their specimens were 1.5–1.7 mm long with a buccal cavity length of 37–38 µm. It is possible that these nematodes were conspecific with the new M. medius .

Type specimens

Holotype female on slide no. 14506. Paratypes: six females and five juveniles; in the nematode collection of the Department of Systematic Zoology and Ecology of the Eötvös Loránd University , Budapest .

Type habitat and locality

Mud from a small pool, Tower Hill State Park near Wisconsin River, Wisconsin, USA . Collected in June 1995 by A. Fodor (Wooster, Ohio, USA) .

Etymology

The species epithet medius (Latin) means medial or mean and refers to the medium size of the buccal cavity.

Figures

Figure 6. Mononchus medius sp. nov. (A) Anterior end; (B) cardial region; (C) vulval region; (D, E) female posterior end. Scale bars 20 µm each.

Figure 7. Mononchus medius sp. nov. (A–C) anterior end; (D) cardial region; (E) mid-body region; (F) vulval region; (G–I) female posterior region.