Sectonema heynsi Altherr, 1968

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 : 70

Sectonema heynsi Altherr, 1968

( Fig. 4 )

Material examined. Female holotype and one juvenile paratype, in poor general condition as the female is visibly flattened and broken in two parts, and some morphological features have become obscure.

Measurements. See Table 1 .

Description. Female: Slender nematode of large size, 6.45 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-shaped, Cuticle three-layered, especially distinct at caudal region, consisting of thin and smooth outer layer, a thicker inner layer bearing radial striation, and a thick inner layer; thickness 4 Μm at anterior region, 8 Μm in mid-body and 14 Μm on tail. Lateral chord 25 Μm wide at mid-body, occupying ca onesixth (?16%) of mid-body diameter. Body pores obscure. Lip region nearly truncate, offset by deep constriction, 3.6 times as wide as high and 18% of body diameter at neck base; lips separate; labial and cephalic papillae distinct but low, weakly protruding; circumoral area bearing cilia- or small setae-like projections. Amphid fovea not observed since the anterior region is in ventral view. Cheilostom as long as wide. Mural tooth (as seen in ventral view) probably typical of the genus, i.e. lacking a distinct dorsal arm, ca three-fourths (70%) of lip region diameter long or 0.31% of body length, and somewhat extruded. Guiding ring weak, plicate. Odontophore linear, rod-like, its precise length difficult to establish. Pharynx distinctly muscular and tripartite, consisting of an anterior thickened spindle-shaped region running from the odontophore base to near the nerve ring, a narrower intermediate section enlarging very gradually, and a basal expansion 10.0 times as long as wide and 5.5 times as long as body diameter, and occupying 68% of total neck length. Pharyngeal gland nuclei obscure. Cardia non-distinguishable. Genital system didelphic-amphidelphic, but only the anterior branch is observable, being 607 µm long and occupying 9% of total body length: ovary large, 303 µm long; oviduct obscure; uterus apparently a simple but long tube 263 µm or?1.7 times the body diameter; vagina?115 µm long or?74% of body diameter, with pars refringens obscure; vulva (as seen in ventral view) a long transverse slit. Prerectum and rectum inconspicuous. Tail short and rounded to rounded conoid, slightly more convex at its dorsal side; caudal pores two pairs, subdorsal, at the middle of tail.

Male: Unknown.

Diagnosis (based on the holotype). Sectonema heynsi is characterized by its body 6.45 mm long, lip region offset by deep constriction and 28 Μm broad, circumoral area bearing cilia- or seta-like structures, mural tooth-like structure 20 Μm long, neck 1256 Μm long, pharyngeal expansion 856 Μm long or 68% of total neck length, uterus a tube-like structure 263 µm or?1.7 times the corresponding body diameter, V = 50, tail short and rounded to conoid (54 Μm, c = 120, c’ = 0.7), and male unknown.

Relationships. Leaving aside the presence of cilia- or seta-like structures covering the circumoral area, S. heynsi is morphometrically very similar to S. demani , another species described by Altherr. The nature of their mural tooth and vagina might be also different, but due the bad condition of the female holotype of S. heynsi , any further comparative analysis is impossible. (See also remarks below.) In having cilia- or seta-like structures covering the circumoral area, a very special feature for dorylaims, S. heynsi resembles S. barbatum Heyns, 1965 , but it can be easily distinguished from this in its much larger general size (vs body length 3.89 mm).

Type locality and habitat. Germany, Reichmannsdorf, Obere Hölle; collected on May 6th, 1965.

Other localities and habitats. Germany, Wildenspring ( Altherr, 1974).

Type material. Female holotype and one juvenile paratype on slide labelled NE 0 97 and 0 96, repectively, deposited with E. Altherr’s nematode collection at the Museo Cantonale di Storia Naturale–Lugano, Switzerland.

Remarks. Sectonema heynsi and S. demani are very similar morphometrically, with no significant difference affecting their most relevant measurements and ratios. The presence of cilia- or seta-like structures covering the circumoral area, a feature originally reported by Altherr (1968) as well, is a remarkable diagnostic feature of S. heynsi and may be the reason why Altherr did not compare both species when describing S. heynsi in spite of their similarity. As mentioned above (see relationships), the morphology of the mural tooth and the vagina might be also different, but, because the female holotype of S. heynsi can only observed in subventral view, it is not possible to provide additional details.

Altherr (1974) reported S. heynsi for the second time in the same geographical area, but he gave a very brief description of one female and one juvenile and did not add any new relevant information about the morphology of the species.

Figures

FIGURE 4. Sectonema heynsi Altherr, 1968 (female holotype, LM). A, B: Anterior region in median, ventral view. C: Caudal region. D: Vulva. (Scale bars A, B, D = 10 µm; C = 25 µm.)