Sectonema septentrionale, Peña-Santiago, Reyes & Álvarez-Ortega, Sergio, 2015

Peña-Santiago, Reyes & Álvarez-Ortega, Sergio, 2015, Description of Sectonema septentrionale sp. n. (Nematoda: Dorylaimida: Aporcelaimidae) from Northern Iberian Peninsula, Zootaxa 3947 (4), pp. 573-580 : 574-579

Sectonema septentrionale sp. n.

( Figs 1–3 )

Material examined. Four females and ten males, in variable state of preservation, from three close localities in Northern Iberian Peninsula, Spain.

Measurements. See Table 1.

Description. Adult: Very slender (a = 47–64) and large nematodes, 5.59–6.90 mm long. Body cylindrical, distinctly tapering towards the anterior end, less so towards the posterior one because the caudal region is rounded. Habitus regularly curved ventrad after fixation, C- or G-shaped. Cuticle three-layered, this layering especially distinct in caudal region, consisting of thin and smooth outer layer, a much thicker intermediate layer bearing radial striation, and a thin inner layer; thickness 4.0–5.5 Μm at anterior region, 5–9 Μm in mid-body and 12–14 Μm on tail. Lateral chord 14–21 Μm wide at mid-body, occupying less than one-fifth (10–18%) of mid-body diameter. Body pores distinct, two dorsal and two ventral pores at cervical region behind the level of the mural tooth base. Lip region offset by constriction, 3.2–3.7 times as wide as high and one-fourth (21–30%) of body diameter at neck base; lips separate, with distinct but low, slightly protruding labial and cephalic papillae. Amphid fovea cup- to stirrup-shaped, opening at level of the cephalic constriction and occupying 12–16 Μm or about one-half (47–58%) of lip region diameter. Cheilostom as long as wide. Mural tooth thick, 2.7–2.9 times longer than its maximum width, occupying most (80–85%) of the stomatal lumen: ventral arm straight, more refractive and 0.64–0.73 times the lip region diameter long; dorsal side sigmoid, less refractive and 0.75–0.86 times the lip region diameter long. Guiding ring weak, plicate, situated at 9–13 µm or 0.4–0.5 times the lip region diameter from the anterior end. Odontophore linear, rod-like, 2.7–3.4 times the odontostyle length. Pharynx distinctly muscular, anterior region enlarging very gradually, basal expansion 10.5–17.6 times as long as wide and 5.4–9.1 times as long as body diameter, and occupying 60–73% of total neck length. Pharyngeal gland nuclei located as follows: DN = 45–49 (n=3), S1N1 = obscure, S1N2 = 72–73 (n=3), S2N = 86, 87 (n=2). Nerve ring located at 207–269 Μm from anterior end or 18–24% of total neck length. Cardia rounded conoid, nearly as long as wide, 15–23 x 19 –25 Μm; a weak ring-like structure is present surrounding its junction to pharyngeal base. Tail short, rounded; its inner core weakly (but visibly) protruding into tail tip. Caudal pores two pairs, at the middle of tail length, one lateral, another subdorsal.

Female: Genital system didelphic-amphidelphic, with both branches equally and well developed, the anterior 675–758 Μm long or 11–12% of body length and the posterior 687–817 Μm long or 11–13% of body length. Ovaries large, reaching the sphincter level, the anterior 221–390 Μm, the posterior 198–403 Μm long; oocytes arranged first in two or more rows, then in a single row. Oviduct 218–286 Μm long or 1.7–2.4 times the corresponding body diameter, and consisting of a slender part with prismatic cells and a well developed pars dilatata. Oviduct-uterus junction marked by a sphincter. Uterus tripartite, consisting of two (proximal and distal) longer and thicker sections with wide lumen, which are separated by an intermediate, shorter and thinner section with narrow lumen; its length 370–493 Μm long or 2.9–4.3 times the corresponding body diameter. Vagina extending inwards 66–75 Μm or 56–66% of body diameter: pars proximalis 36– 52 x 32–36 Μm, with somewhat sigmoid walls and surrounded by weak musculature; pars refringens in lateral view consisting of two trapezoidal to drop-shaped pieces measuring 13–21 x 11 –13 Μm and with a combined width of 24–27 µm; and pars distalis short, 7.5–10.0 Μm long. Vulva a nearly equatorial transverse slit. Prerectum 2.4–3.6, rectum 0.7–1.0 anal body diameters long.

Male: Prerectum 4.2–5.3, cloaca 1.1–1.4 times the corresponding body width long. Genital system diorchic, with opposite testes. Sperm cells spindle-shaped. In addition to the ad-cloacal pair, situated at 16–24 Μm from cloacal aperture, there is a series of 5–11 irregularly spaced ventromedian supplements, 10–81 µm apart, the posteriormost located beyond the range of the spicules and situated at 104–171 Μm from the ad-cloacal pair. Spicule distinctly robust and massive, especially in its posterior half, 3.3–4.0 times its maximum width, 1.4–2.0 times the body diameter at level of the cloacal aperture: dorsal contour regularly convex, ventral contour very weakly concave, lacking distinct hump and hollow; curvature 129-137º; head occupying 13-22% of total spicule length, its dorsal contour conspicuously curved and longer than the ventral, which is very short and straight; median piece 5.5-7.4 times as long as wide, occupying 44-54% of spicule maximum width, reaching the posterior tip; posterior end 13-17 µm wide. Lateral guiding piece 27–45 Μm long, 4.5–8.0 times as long as wide, slightly tapering towards the posterior end, and with somewhat bifid end.

Diagnosis. The new species is characterized by its large size with body 5.59–6.90 mm long and comparatively very slender (a = 47–64), lip region offset by deep constriction and 25–29 Μm broad, mural tooth 18–19 Μm long at its ventral side and occupying most of the stomatal lumen, neck 1024–1304 Μm long, pharyngeal expansion 618– 926 Μm long or 60–73% of total neck length, uterus tripartite and 370–493 Μm long or 2.9–4.3 times the corresponding body diameter, V = 48–52, tail short and rounded (40–62 Μm, c = 108–146, c’ = 0.6–0.8), spicules 100–145 Μm long, and 5–11 irregularly spaced ventromedian supplements bearing hiatus.

Lοcality Pοntοn pass Panderrueda pass Piedrasluengas pass Τοtal range Prοvince Leοn Palencia Hοlοtype Paratypes

Character n ♀ ♂ 3♀♀ 7♂♂ 2♂♂ 4♀♀ 10♂♂ Relationships. Sectonema septentrionale sp. n. is very similar to S. demani Altherr, 1965 (see re-description by Peña-Santiago & Álvarez Ortega 2014a), from which it can be easily distinguished in its more robust mural tooth (occupying nearly whole vs ca 60% of the stomatal lumen), longer (370–493 Μm long or 2.9–4.3 times the corresponding body diameter vs 248–270 µm long or 2.1–2.2 times the corresponding body diameter) and tripartite (with vs without a muscular intermediate region) uterus, and males as frequent as females (vs male unknown).

The new species also resembles S. paramonovi (Eliava, 1966) Eliashvili, Aliev & Eliava, 1977 (= Nygolaimus paramonovi Eliava, 1966 ), a poorly known species described on the basis of only one male, but it differs from this in its rounded tail (vs nearly conical and bearing a distinct dorsal concavity) and larger spicules (100–145 vs 88 µm long).

Type locality and habitat. Northern Iberian Peninsula, León province, Pontón Pass, elevation 1280 m above sea-level, in association with a beech-oak mixed forest and Panderrueda Pass, elevation 1450 m a.s.l., in association with a beech-holly mixed forest. Collected on 16 December, 1994.

Other locality and habitat. Northern Iberian Peninsula, Palencia province, Piedrasluengas Pass, elevation 1355 m a.s.l., in association with a beech-holly mixed forest. Collected on 16 December, 1994.

Type material. Female holotype and one female and six male paratypes deposited in the nematode collection of the Nematology Laboratory at the University of Jaén, Spain. One female and one male paratypes deposited with USDA Nematode Collection, Beltsville, Maryland, USA.

Etymology. The specific epithet is a Latin term meaning ‘northern, from the North’ and refers to the geographical origin of this new species, which dwells in forest soils in the Northern Iberian Peninsula.

Remarks. Together with S. demani , S. septentrionale sp. n. forms part of a group of species within the genus Sectonema that differ from the type species of the genus, S. ventrale Thorne, 1930 (see recent re-description by Peña-Santiago & Álvarez-Ortega 2014b), in the nature of their stomatal protruding structure: a mural tooth vs a reduced odontostyle. The case of S. septentrionale sp. n. is rather peculiar as the mural tooth is comparatively thick or robust, occupying most of the stomatal lumen, but its dorsal side is distinctly longer than the ventral one, somewhat sigmoid and does not join the stomatal dorsal wall.

Figures

FIGURE 1. Sectonema septentrionale sp. n. A: Anterior region in median lateral view. B: Lip region in lateral, surface view. C: Neck. D: Female, anterior genital branch. E: Pharyngo-intestinal junction. F: Female, entire body. G: Male, posterior body region. H: Female, posterior body region. I: Spicule. J: Lateral guiding piece. K: Vagina.

FIGURE 2. Sectonema septentrionale sp. n. Type population from Pontón pass (LM). A, B: Anterior region in median view. C: Male, posterior body region. D: Lip region in surface lateral view. E: Female, caudal region. F: Vagina. G: Female, posterior body region. H: Male, caudal region and spicule. I: Female, intermediate region of uterus. J: Male, sperm cells. (Scale bars: A, B, D-F, H = 20 µm; C, G = 100 µm; I = 50 µm; J = 10 µm.)

FIGURE 3. Sectonema septentrionale sp. n. Type population from Panderrueda pass (LM). A, B: Anterior region in median view. C: Female, posterior body region. D: Female, caudal region. E: Vagina. F: Male, posterior body region. G: Male, caudal region and spicule. H: Male, lateral guiding piece. I: Spicule. (Scale bars: A, D, E, H, I = 20 µm, B = 10 µm; C, F = 100 µm; G = 50 µm.)