Sectonema vietnamense, Nguyen & Abolafia & Bonkowski & Peña-Santiago & Álvarez-Ortega, 2016

Nguyen, Thi Anh Duong, Abolafia, Joaquín, Bonkowski, Michael, Peña-Santiago, Reyes & Álvarez-Ortega, Sergio, 2016, Two atypical new species of the genus Sectonema Thorne, 1930 (Nematoda, Dorylaimida, Aporcelaimidae) from Vietnam, European Journal of Taxonomy 171, pp. 1-20 : 13-18

Sectonema vietnamense sp. nov.

urn:lsid:zoobank.org:act:AF58451E-D7A7-4E49-8A18-9F3998EF4A87

Figs 7–9 , Table 2

Diagnosis

The new species is characterized by a slender (a = 33–49) 2.71–4.25 mm long body, lip region offset by depression and 14–16 μm broad, odontostyle 8–9 μm long at its ventral side, 716–918 μm long neck, pharyngeal expansion 463–618 μm long or 63–67% of total neck length, uterus simple and 209–242 μm long or 2.5–2.9 times the corresponding body diameter, pars refringens vaginae absent, V = 54, short (36 μm, c = 105, c’ = 0.7) and rounded tail in female and slightly more conoid (34–39 μm, c = 70– 115, c’ = 0.6–0.8) in male, 59–75 μm long spicules, and three or four irregularly spaced ventromedian supplements bearing hiatus.

Etymology

The specific epithet refers to the geographical origin of the species.

Type material examined

Holotype

VIETNAM: ♀, in good state of preservation, Northern Vietnam , Cuc Phuong National Park, pristine tropical forest, deposited in the nematode collection of the University of Jaén, Spain.

Paratypes

VIETNAM: 4 ♁♁, 3 juvs, in good state of preservation, same data as holotype; 1 ♁, in good state of preservation, same locality, deposited in the nematode collection of the Institute of Ecology and Biological Resources, Hanoi, Vietnam; 1♁, 1 juv., same locality, used for SEM.

Other material examined

VIETNAM: 2 ♁♁, in acceptable state of preservation, Northern Vietnam, Thái Bình province, intensively cultured field, deposited in the nematode collection of the University of Jaén, Spain.

Description (type population)

Adult

Very slender nematodes of big size, 3.13–4.25 mm long. Body cylindrical, distinctly tapering towards the anterior end, less so towards the posterior one as the caudal region is rounded. Habitus regularly curved ventrad after fixation, to a more or less open C, occasionally more curved at posterior body region. Cuticle 2.0–2.5 μm thick at anterior region, 3.0–4.5 μm in mid-body and 8–10 μm on tail; consisting of three layers especially distinguishable at caudal region: thinner outer layer bearing very fine transverse striation through the entire body, thicker intermediate layer with radial striation, and thin inner layer. Lateral chords 6–12 μm wide at mid-body, occupying up to one-sixth (8–15%) of mid-body diameter. Two ventral and two dorsal body pores often present at level of stoma, and four distinct lateral pores 6–20 μm apart visible behind the amphid fovea. Lip region nearly continuous (a shallow depression is, however, often perceptible), weakly angular, visibly narrower than adjacent body, 2.1–2.3 times wider than high and about one-fifth (18–23%) of body diameter at neck base; it appears (under SEM) marked by radial (oral field) or longitudinal (remaining lip region) incisures, with amalgamated lips and protruding, pore-like labial and cephalic papillae, all of them surrounded by a ring-like annulus, and the inner labial papillae visibly larger than the outer ones; oral field perceptibly hexagonal, oral aperture a dorso-ventral slit, the lip region hence showing a bi-radial symmetry. Cupshaped amphid fovea, its opening at level of cephalic depression and occupying 10–11 μm or 68–72% of lip region diameter. Nearly cylindrical cheilostom, without differentiation. Odontostyle comparatively short and occupying the whole stomatal lumen, its ventral side 0.5–0.6 times longer than lip region diameter and 0.20–0.29% of body length. Guiding ring simple, somewhat plicate, at 0.5 times the lip region diameter from anterior end. Odontophore linear, rod-like, 3.7–4.2 times the odontostyle length. Tripartite pharynx, consisting of an anteriorly thickened section behind the odontophore base, a perceptible narrower intermediate section with the nerve ring surrounding it, which enlarges very gradually into the basal expansion 9.9–15.0 times longer than wide, 6.7–7.3 times longer than body diameter and occupying 63–67% of total neck length; gland nuclei mostly obscure, only S 2 N are visible, at 77–78% (n = 3) of total neck length. Nerve ring located at 147–178 μm from anterior end or 19–22% of total neck length. Cardia rounded conoid, 15–19 × 12–17 μm; a ring-like structure is present surrounding its junction to pharyngeal base.

Female

Genital system didelphic-amphidelphic, with almost equally and well developed branches, the anterior 473 μm long or 13% of body length and the posterior 387 μm long or 10% of body length, each branch bearing one uterine egg. Moderately sized ovaries, not surpassing the sphincter level, the anterior 191 μm, the posterior 141 μm long; oocytes arranged first in two or more rows, then in a single row. Oviduct 117, 142 μm long or 1.4, 1.7 times the corresponding body diameter, and consisting of a slender part made of prismatic cells and a well developed pars dilatata with wide lumen and sperm cells inside. Oviduct-uterus junction marked by a sphincter. Uterus a simple, tube-like structure 209, 242 μm long or 2.5, 2.9 times the corresponding body diameter, containing abundant sperm cells and one uterine egg. Vagina extending inwards 36 μm or about three-sevenths (44%) of body diameter: pars proximalis 23 × 28 μm, somewhat sigmoid walls and surrounded by weak musculature; pars refringens absent; pars distalis well developed, 15 μm long. Vulva a post-equatorial transverse slit. Prerectum 3.0, rectum 0.9 anal body diameters long. Short and rounded tail, its inner core with a finger-like projection at tail end; two pairs of caudal pores, one sub-lateral, another sub-dorsal.

Male

Genital system diorchic, with opposite testes. In addition to the ad-cloacal pair, situated at 14–19 μm from cloacal aperture, there is a series of three or four irregularly spaced, 15–48 μm apart, ventromedian supplements, the posteriormost of which lying out the range of retracted spicules, at 76–91 μm from the ad-cloacal pair. Spicule robust and massive, especially in its posterior half, 3.6–4.6 times its maximum width, 1.3–1.4 times the body diameter at level of the cloacal aperture: dorsal contour regularly convex, ventral contour slightly concave, with distinct hump and hollow; curvature 125–136º; head occupying 13–19% of spicule total length, its dorsal contour distinct curved at its anterior end and longer than the ventral one, which is short and almost straight; median piece 5.9–7.1 times longer than wide, occupying 52–65% of spicule maximum width, reaching the posterior tip; posterior end 6–7 μm wide. Lateral guiding pieces 15–17 μm long, 5.3–6.5 times longer than wide. Prerectum 4.3–5.7, cloaca 1.0–1.3 times the corresponding body width long. Rectal glands and their ducts (cf. Coomans & Loof 1986) very well perceptible ( Fig. 8K ). Cloacal aperture, as seen under SEM, a somewhat curved anteriad, transverse slit; the two supplements of the precloacal pair distinctly separated. Tail a little more conoid than that of female; two pairs of caudal pores, one almost lateral, another sub-dorsal.

Relationships

The new species is easily distinguishable from its congeners in the unique combination of these features: narrow and nearly continuous lip region, very short odontostyle, absence of pars refringens vaginae and short and rounded tail. Nonetheless, it resembles S. barbatum Heyns, 1965 in its general morphology, but it can be distinguished from this because of its oral field lacking any setae-like structure (vs bearing numerous short forwardly pointing setae), narrower (14–16 vs about 22 μm broad) lip region, shorter (8–9 vs 16 μm) odontostyle, pars refringens vaginae absent (vs present), shorter (36 μm, c = 105, c’ = 0.7 vs 48 μm, c = 81, c’ = 1.0) female tail, and male present (vs absent). In having a comparatively small body size and nearly continuous lip region, S. vietnamense sp. nov. is close to S. mucrodens and S. truxum , from which it differs in its narrower (14–16 vs more than 20 μm broad) lip region, shorter stomatal protruding structure (8–9 vs more than 20 μm) located as usual (vs the anterior tip distinctly behind the level of guiding ring), and pars refringens vaginae absent (vs consisting of two small pieces). Sectonema vietnamense sp. nov. is also similar to S. pseudoventrale Heyns, 1965 in having a short odontostyle, but can be distinguished from this by its narrower (14–16 vs 21–23 μm broad) lip region, shorter (209–242 μm or 2.5–2.9 times the corresponding body diameter vs 123 μm or 1.3 times the corresponding body diameter) uterus, shorter (36 μm, c = 105, c’ = 0.7 vs 46–63 μm, c = 82–130, c’ = 0.8–1.0) female tail, shorter (59– 75 vs 90–95 μm) spicules, and fewer (three or four vs six or seven) ventromedian supplements. Finally, the new species also resembles S. tropicum sp. nov., but it can be distinguished from this by its narrower (14–16 vs 19–21 μm broad) lip region, shorter (8–9 vs 20–21 μm at its ventral side) odontostyle, longer (occupying 63–67 vs 52–59% of total neck length) pharyngeal expansion, more posterior vulva ( V = 54 vs V =48–52), pars refringens vaginae absent (vs present), shorter (59–75 vs 91–97 μm) spicules and higher number of ventromedian supplements (three or four vs one).

Remarks

The two males from Thái Bình are very similar to those of the type population, but some minor morphometric differences have been also noted: somewhat smaller (2.71, 3.02 vs 3.13–4.25 mm long) and more obese (a = 33, 35 vs a = 41–49) body. Such differences have been regarded as instraspecific variation as the number of specimens examined is low and the main morphological and morphometric features are coincident.

Figures

Fig. 7. Sectonema vietnamense sp. nov. (Line). A. Anterior region in median, lateral view. B. Lip region in surface, lateral view. C. Neck region. D. Vagina. E. ♀, anterior genital branch. F. ♁, entire. G. ♀, entire. H. ♁, posterior body region. I. ♀, posterior body region. J. Spicule. K. Lateral guiding piece.

Fig. 8. Sectonema vietnamense sp. nov. (LM, type population). A. ♁, entire. B–C. Anterior region in lateral, median view. D. ♀, anterior genital branch. E. ♁, posterior body region. F. Oviduct-uterus junction. G. Lip region in lateral, surface view. H. Vagina. I. ♁, caudal region. J–K. Spicules. L. ♀, caudal region. Scale bars: A = 500 μm; B–C, H = 10 μm; D = 100 μm; E–F = 50 μm; G = 5 μm; I–L = 20 μm.

Fig. 9. Sectonema vietnamense sp. nov. (SEM, A = juvenile and B–J = ♁). A. Lip region in ventral view. B–C. Lip region in lateral view. D. Posterior body region in ventral view. E. Lip region in frontal view. F. Detail of a ventromedian supplement. G. Caudal region in lateral view. H. Caudal region in subventral view. I. Detail of the ad-cloacal pair of supplements. J. Caudal region in ventral view. Scale bars = A–C, E = 2 μm; D = 20 μm; F, I = 1 μm; G–H = 10 μm; J = 5 μm.