Sectonema demani Altherr, 1965

Peña-Santiago, R. & Álvarez-Ortega, S., 2014, Re-description of three species of the genus Sectonema Thorne, 1930 (Nematoda: Dorylaimida: Aporcelaimidae) originally studied by E. Altherr, Zootaxa 3881 (1), pp. 63-74 : 64-69

Sectonema demani Altherr, 1965

( Figs 1–3 )

Material examined. Female holotype, in bad condition as the nematode has become broken into four parts, but some relevant morphological features are distinguishable. One female from Brabant ( Belgium), in excellent condition.

Measurements. See Table 1 .

Prerectum length 288 314?? 182? Rectum⁄Clοaca length 70 85?? 75 84 Τail length 51 55 32 54 62 58 Spicule length - - - - - 107 ventrοmedian supplements - - - - - 8

Calculated frοm οriginal descriptiοn.

Description. Female holotype ( Fig.1 ): Slender nematode of large size, estimated at 7.24 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, probably C-shaped. Cuticle three-layered, especially distinct at caudal region, consisting of thin and smooth outer layer, a very thicker intermediate layer bearing radial striation, and a thin inner layer; thickness 4.5 Μm at anterior region, 5.5 Μm in mid-body and 13 Μm on tail. Lateral chords obscure. Body pores distinct, four lateral ones at cervical region, at 9, 37, 72 and 79 µm from the lip region constriction. Lip region nearly truncate, offset by deep constriction, 3.7 times as wide as high and 23% of body diameter at neck base; lips separate; labial and cephalic papillae distinct but low, weakly protruding. Amphid fovea not observed as the anterior region is seen in ventral view. Cheilostom apparently as long as wide since the guiding ring is not perceptible. Ventral side of mural tooth ca three-fourths (74%) of lip region diameter long or 0.28% of body length. Odontophore rod-like, without any differentiation. Pharynx distinctly muscular and tripartite, consisting of an anterior thickened spindle-shaped region, a narrower intermediate section enlarging very gradually, and a basal expansion 11.2 times as long as wide, 7.4 times as long as body diameter and occupying 68% of total neck length. Pharyngeal gland nuclei obscure. Nerve ring also obscure. Morphology of cardia not distinguishable. Genital system didelphic-amphidelphic, but some details of its morphology remain difficult to elucidate: ovaries large, barely surpassing the oviduct-uterus junction; oviduct ca 310 µm long or 2.1 times (probably more as the specimen is visibly flattened) the corresponding body diameter, with an elongate pars dilatata; oviduct-uterus junction marked by a distinct narrowing; uterus apparently a simple tube-like structure ca 270 µm long or 1.8 times the corresponding body diameter; pars refringens vaginae seems to be present and welldeveloped; vulva (as observed in ventral view) a long transverse slit. Prerectum 3.8, rectum 0.9 anal body diameters long. Caudal region short and rounded, slightly more convex at its dorsal side; inner core weakly protruding at tail tip. Caudal pores two pairs, subdorsal, at the middle of tail.

Male: Unknown.

One female from Brabant, Belgium ( Figs 2 & 3 ): Comparatively very slender (a = 56) and large nematode, 6.78 mm long. Body cylindrical, distinctly tapering towards the anterior end, less so towards the posterior one because the caudal region is rounded conoid. Habitus regularly curved ventrad after fixation, C-shaped. Cuticle three-layered, especially obvious at caudal region, consisting of a thin and smooth outer layer, a thick intermediate layer bearing radial striation and fine criss-cross lines through the entire body ( Fig. 3 K), and thinner inner layer; thickness 4 Μm at anterior region, 5.5 Μm in mid-body and 13 Μm on tail. Lateral chord 20 Μm wide at mid-body, occupying about one-seventh (17%) of mid-body diameter. Body pores distinct, three dorsal and three ventral pores at level of the mural tooth plus odontophore. Lip region offset by deep constriction, 3.7 times as wide as high and ca one-fourth (24%) of body diameter at neck base; lips separate, their inner region probably differentiated in perioral lobes; labial and cephalic papillae distinct but low, weakly protruding. Amphid fovea cup-shaped, opening at level of the cephalic constriction and occupying 12 Μm or hardly less than one-half (45%) of lip region diameter. Cheilostom nearly cylindrical, lacking any differentiation. Ventral side of mural tooth straight, 3.3 times longer than its width at the base, and 0.7 times the lip region diameter long or 0.29% of total body length; dorsal side sigmoid, slightly longer than the ventral one and visibly refractive at its base; mural tooth base 6 Μm wide, visibly narrower (60%) than the stomatal lumen. Guiding ring weak, very plicate, at 13 Μm or 0.5 times the lip region diameter from the anterior end. Odontophore linear, rod-like, ca twice (2.1 times) the mural tooth length. Pharynx typical of the genus, tripartite, consisting of a comparatively thick anterior region, a short narrower intermediate part (enveloped by the nerve ring) enlarging very gradually, and the basal expansion 13.2, times as long as wide, 7.2 times as long as body diameter, and occupying 69% of total neck length. Pharyngeal gland nuclei located as follows: DN = 44; S1N1 = 65; S1N2 = 76; S2N = 87. Nerve ring located at 270 Μm from the anterior end or at 22% (n = 2) of total neck length. Cardia rounded conoid, 16 x 23 Μm, its junction to pharyngeal base surrounded by a thick ring-like structure; intestine enveloping the cardia at about its middle and forming a short conical extension protruding into the intestinal lumen. Intestine cells especially distinct, six to eight in diameter, with very well perceptible membrane, nucleus and protoplasmic granules ( Fig. 3 J). Many granular, pseudocoelomocyte bodies present at the posterior body region, predominantly in lateral and dorsal position ( Fig. 3 L). Genital system didelphic-amphidelphic, with both branches almost equally and well developed, the anterior 553 Μm long or 8% of total body length and the posterior 563 Μm long or 8% of total body length: ovaries relatively small, not reaching the level of the oviduct-uterus junction, the anterior 186, the posterior 193 Μm long, with oocytes arranged first in two or more rows, then in a single row; oviduct 243–248 Μm long or 2.0–2.1 times the corresponding body diameter, and consisting of a slender part with prismatic cells and a well developed pars dilatata with perceptible lumen; oviduct-uterus junction marked by a very distinct narrowing surrounded by a muscular ring; uterus a simple, tube-like structure 248–267 Μm long or 2.1–2.2 times the corresponding body diameter; vagina extending inwards 85 Μm or 71% of body diameter, with pars proximalis 60 x 51 Μm, somewhat sigmoid walls and surrounded by weak musculature, pars refringens with two close together trapezoidal pieces measuring 22 x 18 Μm and a combined width of 37 µm, and pars distalis 6 Μm long. Vulva a nearly equatorial transverse slit. Prerectum 4.4, rectum 1.2 anal body diameters long. Tail short, rounded conoid, slightly straighter at its ventral side; inner cuticle layer showing a gap (more transparent area) at tail tip. Caudal pores two pairs, one sublateral, another subdorsal, at the middle of tail.

Diagnosis (based on female holotype and the Belgian female). This species is characterized by its 6.78–7.24 mm long body, lip region offset by deep constriction and 27–28 µm broad, mural tooth 19–20 µm long at its ventral side and 21 µm at its dorsal one with its base 6 µm wide or three-fifths of the stomatal lumen, neck 1217–1290 µm long, pharyngeal expansion 834–875 µm long or 68–69% of total neck length, female genital system didelphicamphidelphic, uterus a simple tube-like structure measuring 248–270 µm long or 2.1–2.2 times the corresponding body diameter, pars refringens vaginae well developed, V = 49–52, tail short and rounded conoid (51–55 µm, c = 123–143, c’ = 0.7–0.8), and male unknown.

Relationships. Sectonema demani morphometrically resembles S. ventrale Thorne, 1930 , but it can be easily distinguished from this in the nature and size of its stomatal protruding structure (vs a reduced odontostyle rather than a mural tooth, 12–14 µm long, with its base occupying nearly the whole stomatal lumen, according to the recent re-description by Peña-Santiago & Álvarez-Ortega, in press). It is also similar to S. paramonovi (Eliava, 1966) Eliashvili, Aliev & Eliava, 1977 , a poorly characterized species, originally described on the basis of only one male specimen. Sectonema demani and S. paramonovi may be identical but available information (based on different sexes) does not allow their detailed comparison.

Type locality and habitat. Germany, Rhine river near Krefeld, in groundwater; collected on October 29th, 1958.

Other localities and habitats. Hungary, near Budapest, Hársbokorhegy, in the soil of an oak forest ( Andrássy, 1984, 1990, 2009). Belgium, province of Brabant (present study). See also remarks regarding one other suspected record by de Man (1921) from the Netherlands.

Type material. Female holotype on slide labelled NE 287, deposited with E. Altherr’s nematode collection at the Museo Cantonale di Storia Naturale–Lugano, Switzerland.

Remarks. The above description of female holotype perfectly fits the original one by Altherr (1965), but very small morphometric differences can be noted, certainly due to subjective perception and/or the use of different microscopic devices.

Loof (1961) considered that the female specimen described by de Man (1921) from the Netherlands as Dorylaimus robustus might belong to an undescribed species of Sectonema . In his turn, in describing the new species S. demani, Altherr (1965) discussed that de Man’s female might be identical with his new species as their respective morphometrics are very similar. A comparative analysis (see Table 1 ) shows that the female reported by de Man actually is nearly identical morphometrically to Altherr’s holotype, but also that its caudal region is significantly shorter (32 vs 51 µm, c = 143 vs c = 225, c’ = 0.4 vs c’ = 0.7). Thus, some doubt persists on the true identity of this specimen, which might rather belong to S. brevicauda Heyns, 1965 .

Andrássy (1984, 1990, 2009) reported the presence of S. demani in Hungarian soils, but no description of this material was provided by the author.

The female from Brabant has been tentatively regarded as being conspecific with the holotype since, as far as they can be compared—as mentioned, the holotype is in bad condition and its anterior region is not observed in lateral view, actually a handicap for comparative purposes—their main diagnostic features (lip region, mural tooth, female genital system, caudal region, etc.) are nearly identical, their morphometrics are very similar, and both occur in West Central Europe ( Germany and Belgium, respectively).

The mural tooth of S. demani , as observed in the Brabant female, differs from that found in S. ventrale , the type species of the genus (see details in Peña-Santiago & Álvarez-Ortega, in press) in two main aspects. First, its dorsal side is slightly sigmoid (vs forming a perceptible concavity or nearly right angle at its posterior part) and visibly (vs hardly) longer than the ventral one. Second, and more importantly, it is conspicuously narrower (ca 60%, see above) than the stomatal lumen as the dorsal side does not join the dorsal wall of the stoma at all. Thus, it should be regarded as a true mural tooth (vs a reduced odontostyle in contrast to a typical mural tooth in S. ventrale ). In both cases, however, the dorsal side of the protruding structure seems to be equally and significantly reduced. As far as is known, the functional meaning of this remarkable difference remains obscure. Its taxonomic importance will be a matter for further studies, when more species of the genus are better characterized.

Figures

FIGURE 1. Sectonema demani Altherr, 1965 (female holotype, LM). A: Anterior region in part, showing the location of the three most anterior lateral pores. B: Anterior region in median, ventral view. C: Posterior body region. D: Caudal region. (Scale bars: A, B = 10 µm; C = 100 µm; D = 20 µm).

FIGURE 2. Sectonema demani Altherr, 1965 (female from Brabant, Belgium; Line drawings). A: Anterior region in median lateral view. B: Lip region in lateral, surface view. C: Vagina. D: Neck. E: Anterior genital branch. F: Pharyngointestinal junction. G: Entire body. H: Posterior body region. I: Caudal region.

FIGURE 3. Sectonema demani Altherr, 1965 (female from Brabant, Belgium; LM). A, B: Anterior region in lateral, median view. C: Anterior part of neck region. D: Posterior genital branch. E: Lip region in lateral, surface view. F: Vagina. G: Pharyngo-intestinal junction. H: Posterior uterus. I: Caudal region. J: Intestine cells. K: Criss-cross lines in the cuticle. L: Pseudocoelomic bodies. M: Oviduct-uterus junction. (Scale bars: A, F, J, K = 20 µm; B, E = 10 µm; C, G, I, L, M = 50 µm; D = 200 µm; H = 100 µm.)

Tables

TABLE 1. Mοrphοmetrics οf Sectonema demani Altherr, 1965, Dorylaimus robustus apud de Man 1921 nec de Man, 1876, S. heynsi Altherr, 1968, and S. macrospiculum Altherr, 1958) Heyns, 1965. Measurements in μm (except L, in mm), and in the fοrm ∶ mean ± standard deviatiοn (range).

Species Pοpulatiοn Character	S. demani Near Krefeld , Brabant, Belgium Germany Hοlοtype n ♀ ♀	D. robustus Middelburg , Netherlands ♀	S. heynsi Reichmannsdοrf, Germany Hοlοtype ♀	S. macrospiculum Near Deichhausen , Germany Hοlοtype Paratype ♀ ♂
L a	7.24 6.78 48 56	7.25 56	6.45 41	5.06 4.07 35 37
b	5.6 5.6	5.1	5.1	5.4 4.9
c c'	143 123 0.7 0.8	225 0.4*	120 0.7	82 71 0.7 0.8
v Lip regiοn diam. Οdοntοstyle length - ventral side Οdοntοphοre length Guiding ring frοm ant. end Neck length Pharyngeal expansiοn length Diam. at neck base at midbοdy at anus	49 52 27 28 20 19 42 43? 13 1290 1217 875 834 118 116 150 120 77 71	52* 29 19* 46*? 1415 1015 122 140 76	50 28 20?? 1256 856 156 156 81	53 - 27 28 15 15 32 30 13 14 935 823 640 555 137 111 144 111 88 74