Metaxonchium nobile, Andrássy, 2010

Andrássy, I., 2010, Two New Species Of Dorylaimida (Nematoda) From The Mediterranean Region, Acta Zoologica Academiae Scientiarum Hungaricae 56 (3), pp. 201-210 : 206-210

Metaxonchium nobile sp. n.

( Figs 4 A–F , 5 A–B and 6 A–F )

Holotype female: L = 3.27 mm; a = 37; b = 3.6; c = 80; c’ = 0.9; V = 47%.

Paratype males (n = 2): L = 2.96–3.59 mm; a = 40–46; b = 3.3–3.6; c = 70–97; c’ = 0.8–0.9.

Type specimens. Holotype female on slide No. 15002. Paratypes: two males. Type specimens will be deposited at the Hungarian Natural History Museum.

Type habitat and locality. Wet soil from a grassland, Zlatibor Plateau, north of Nova Varoš, Serbia; collected in October 2004 by J. KONTSCHÁN (Budapest) .

General description. Large and slender nematodes with more or less ventrally arcuate body; body 74–88 µm wide at mid-region. Cuticle very finely striated transversely (practically smooth), 3.5–4.5 µm thick on mid-body, and 8.5–10.0 µm thick on tail, with two main layers: outer layer subdivided into two secondary layers (under light microscope); outer and inner layers nearly equally thick on the anterior half of the body, inner layer strongly thickened posteriorly, especially on tail. On both sides of the anterior neck region, between the cuticle and somatic musculature, a roomy lacuna can be observed. Lip region small, 12–13 µm wide, offset by a deep constriction; lips also small, separate, anteriorly pointed with minute papillae. Body just posterior to lips narrower than the subsequent region, neck-like, at posterior end of oesophagus 6–7 times as wide as head. Amphids cup-shaped with apertures occupying nearly three quarters of corresponding body width.

Odontostyle fusiform, 12–13 µm long, as long as the lip region width, about as thick as cuticle at the same level. Aperture occupying one quarter of stylet length. Odontophore rod-like. Guiding ring simple, thin. Oesophagus 886–990 µm long consisting of a slender anterior tubular part and a much longer, highly muscular posterior portion, separated from the anterior part by a constriction. Expanded part of oesophagus (cylindrus) 636–720 µm long, occupying 61–63% of the entire length of oesophagus; surrounded by fairly thick muscle sheath of straight bundles. Dorsal oesophageal nucleus prominent, large, located at 30–31% of oesophagus length or 8.3–9.3% of total body length. Ventrosublateral nuclei, as usual in Axonchiinae, inconspicuous. Glandularium 610–690 µm long. Cardia tongue-like, broad, 34–48 µm long, surrounded by thin intestinal tissue.

Female. Reproductive system pseudo-opisthodelphic, consisting of a long prevulval uterine sack plus a rudimentary oviduct (or ovary?), and a long postvulval uterus, an oviduct and a long reflexed ovary. Anterior genital branch 3.5 times the body diameter long or occupying 9% of body length, posterior branch 7.0 times the body width long or occupying 18% of body length. Vulva transverse, oval with large, heart-shaped and heavily sclerotized inner lips. Vagina 56 µm long, extending two-thirds across the body. Uterine eggs not observed. No echinulate bodies (Z-differentiation) in uterus. Prerectum 8 times, rectum 1.3 times as long as anal body diameter. Distance between posterior end of oesophagus and vulva shorter (0.7 times) than oesophagus. Vulva–anus distance equal to anterior genital branch, F = female tail. (Scale bars 20 µm each)

41 tail lengths. Tail hemispheroid with small submammillate terminus and strongly thickened cuticle, 38 µm long, occupying 1.2% of entire body length. Two pairs of caudal pores.

Male. Similar to the female in most respects. Testes two. Spermatozoa ovoid, 8–10 µm long. Spicula slightly arcuate, 98–106 µm long, 2.4–2.6 times as long as tail, slender with an unusually long and strongly tapered anterior part (neck). Supplements consisting of double adcloacal papillae, preceded by 9 or 10, small, well-spaced ventromedial supplements, posterior two of them located within the spicular range. Series of supplements 196–208 µm long. Prerectum 9–12 times anal body width long, beginning 1.4–1.6 body widths before the anteriormost supplement. Tail similar to that of female, rounded, 38–42 µm long, occupying 1.0–1.4% of total body length. Three pairs of caudal pores present.

Main characters and relationships. Metaxonchium nobile sp. n. is characterized by a long body, practically smooth cuticle, neck-like narrowing behind lips, roomy lacuna at cervical region, very long cylindrus, long prerectum, sclerotized vulval lips, long vagina, relatively long prevulval genital branch, uterus without echinulate bodies, unusually long and proximally strongly attenuated spicula, spaced supplements, and by the short spheroid tail.

In the shape and size of the body, length of the odontostyle, strongly sclerotized vulval lips, presence of an anterior rudimentary genital portion, shape and length of the tail, number of the ventromedial supplements, the new species strongly resembles Metaxonchium coronatum (DE MAN, 1906) COOMANS & NAIR, 1975 . However, it differs from the sister species (as characterized by THORNE 1939, NAIR & COOMANS 1974, and POPOVICI 1990) by the smooth cuticle (vs. distinctly annulated), the neck-like narrowing behind the head, the presence of conspicuous lacunae on the neck region, the length and, particularly, by the shape of the long-necked spicula (96–104 vs. 78–87 µm, or 2.4–2.6 vs. 1.5–1.9 anal body diameters long), and by the presence of two supplements (vs. one) within the spicular range.

In having so long-necked spicula, Metaxonchium nobile sp. n. is unique within the genus. Two species can be compared with it that have somewhat tapered spicula proximally, M. macrophallum THORNE, 1939 and M. giennense PEÑA- SANTIAGO et COOMANS, 1990. The new species is easily distinguished from them in the much longer (96–104 vs. 66–87 µm) and more strongly attenuated spicula, and by the non-echinulate uterus.

Etymology. Latin nobile meaning noble refers to the illustrious appearance of this species.

Figures

Fig. 4. Metaxonchium nobile sp. n.: A = anterior end, B = cervical region, with large lacunae, C = junction between the two sections of the oesophagus, D = cardial region, E = vulval region, with the

Fig. 5. Metaxonchium nobile sp. n.: A = posterior region of male, B = male posterior end. (Scale bars 20 µm each)

Fig. 6. Metaxonchium nobile sp.n. microphotos: A = anterior end, B = oesophago-intestinal junction, C = vulval region, D = female posterior end, E–F = male spicular region