Sectonema macrospiculum ( Altherr, 1958 ) Heyns, 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 : 71-72

Sectonema macrospiculum ( Altherr, 1958) Heyns, 1965

( Fig. 5 )

Syn. Nygolaimus macrospiculum Altherr, 1958

Material examined. Female holotype, one male paratype and one juvenile paratype in acceptable state of preservation, but flattened.

Measurements. See Table 1 .

Description. Adult: Slender nematodes of large size, 4.05, 5.06 mm long. Body cylindrical, distinctly tapering towards the posterior end, less so towards the anterior one because the caudal region is rounded conoid. Habitus somewhat sigmoid after fixation. Cuticle three-layered, especially obvious at caudal region, consisting of a thin outer layer bearing weak transverse striation, a thick intermediate layer bearing radial striation and fine criss-cross lines through the entire body, and thinner inner layer; thickness 4 Μm at anterior region, 3.5 Μm in mid-body and 7, 10 Μm on tail. Lateral chord 16, 19 Μm wide at mid-body, occupying about one-seventh (14, 13%) of mid-body diameter. Body pores distinct, two dorsal and two ventral pores at cervical region behind the level of odontophore base; fine ventral pores also visible throughout the entire body. Lip region offset by constriction, 3.6 times as wide as high and 25, 20% of body diameter at neck base; lips separate, with labial and cephalic papillae distinct but low, weakly protruding. Amphid fovea cup- to stirrup-shaped, opening at level of the cephalic constriction and occupying 14 Μm or about one-half (49, 52%) of lip region diameter. Cheilostom nearly cylindrical, lacking any differentiation. Stomatal protruding structure an odontostyle similar to that found in S. ventrale (see recent redescription by Peña-Santiago & Álvarez-Ortega, in press): ventral side 0.5 times as long as lip region diameter or 0.36, 0.29% of body length, and 3.7, 3.3 times as long as its width at the base; dorsal side with very long aperture showing a weak but perceptible concavity at its posterior part, and a very short refractive terminal part apparently joining the dorsal wall of the stoma. Guiding ring weak, plicate, situated at 14, 13 µm or 0.49 times the lip region diameter from the anterior end. Odontophore linear, rod-like, 2.0, 2.2 times the mural tooth length. Anterior region of the pharynx slender but distinctly muscular, enlarging very gradually; basal expansion 8.8, 10.0 times as long as wide, 5.0, 4.7 times as long as body diameter, and occupying 67, 68% of total neck length. Pharyngeal gland nuclei obscure. Nerve ring located at 194, 215 Μm from anterior end or 24, 23% of total neck length. Cardia rounded conoid, 28 x 23, 27 Μm; a weak ring-like structure is present surrounding its junction to pharyngeal base. Intestine containing setae as result of the digestion of oligochaete prey.

Female: Genital system didelphic-amphidelphic, with both branches almost equally and well developed, the anterior 562 Μm long or 11% of body length and the posterior 585 Μm long or 12% of body length. Ovaries large, usually surpassing the sphincter level, the anterior 294 Μm, the posterior 305 Μm long, with oocytes arranged first in two or more rows, then in a single row. Oviduct 237–240 Μm long or 1.6–1.7 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 a simple tube-like structure, 270–297 Μm long or 1.9–2.1 times the corresponding body diameter; vagina extending inwards 77 Μm or 54% of body diameter: pars proximalis 59 x 33 Μm, with somewhat sigmoid walls and surrounded by moderately developed, circular musculature; pars refringens with two trapezoidal pieces measuring 15 x 10.5 Μm and a combined width of 31 µm; and pars distalis short, 6 Μm long. Vulva a slightly post-equatorial transverse slit. Prerectum 2.1, rectum 0.8 anal body diameters long. Tail short, convex conoid; caudal pores not well perceptible.

Male: General morphology similar to that of females. Genital system diorchic, with opposite testes. In addition to the ad-cloacal pair, situated at about 21 Μm from the cloacal aperture, there is a series of eight irregularly spaced, 12–17 µm apart, ventromedian supplements, the posteriormost of which is located at 79 Μm from the ad-cloacal pair, out the range of spicules. Spicules very robust and massive especially at its posterior half, 2.8 times as long as wide, and 1.4 times as long as cloacal body diameters; dorsal side regularly convex, ventral one very weakly concave, lacking distinct hump and hollow; curvature 127º; head very short, occupying 7% of spicule total length, its dorsal side weakly curved and longer than the ventral one, which is extremely short; median piece 4.1 times as long as wide, occupying 60% of spicule maximum width, reaching the terminal tip; posterior end 13 µm wide. Lateral guiding piece 25 Μm long, 5.0 times as long as wide. Prerectum obscure, cloaca hardly longer (1.1 times) than the corresponding body width long. Tail more conoid than that of female, but with the ventral side visibly more straight; caudal pores obscure.

Juvenile: General morphology similar to that of adults. Both the functional and the substitution odontostyle equally developed and 14 µm long.

Diagnosis. Sectonema macrospiculum is characterized by its 4.07–5.06 mm long and slender (a = 35–37) body, lip region offset by deep constriction and 27–28 Μm broad, ventral side of odontostyle 15 Μm long, neck 823–935 Μm long, pharyngeal expansion 555–640 Μm long or 67–68% of total neck length, uterus a simple tube-like structure 270–297 Μm long or 1.9–2.1 times the corresponding body diameter, pars refringens vaginae with two well developed sclerotized pieces, V = 53, female tail short and convex conoid with rounded terminus (62 Μm, c = 82, c’ = 0.7), male tail more conoid thant that of female and with the ventral side visibly more straight (58 Μm, c = 71, c’ = 0.8), spicules 107 Μm long, and eight irregularly spaced ventromedian supplements bearing hiatus.

Relationships. Sectonema macrospiculum is very similar to S. pseudoventrale Heyns, 1965 and S. ventrale . It differs from S. pseudoventrale in its wider lip region (vs 22–23 µm wide), larger odontostyle (vs 9 µm long), longer uterus (vs about 123 µm or 1.3 times the body diameter), and longer spicules (vs 90–95 µm). It can be distinguished from S. ventrale in its smaller general size (vs body 7.09–10.42 mm long), caudal region relatively longer (vs c> 100), and longer spicules (vs 120 µm).

Type material. Female holotype and one male and one juveniles paratypes on slide labelled NE 0 0 9, deposited with E. Altherr’s nematode collection at the Museo Cantonale di Storia Naturale–Lugano, Switzerland.

Distribution. This species is only known to occur in its type locality in Germany, near Deichhausen, Germany, where it was collected from seepage water in the banks of the Weser River.

Remarks. The above description perfectly fits the original one as well the re-description (based on type specimens) provided by Heyns (1965), although new morphological details are herein given, especially those regarding the odontostyle and the genital system of both the female and the male.

Figures

FIGURE 5. Sectonema macrospiculum (Altherr, 1958) Heyns, 1965 (type material, LM). A: Female, anterior part of neck region. B, C, G: Anterior region in lateral, median view of female, male and juvenile, respectively. D: Female, lip region in lateral, surface view. E: Vagina. F: Female, posterior body region. H: Male, posterior body region. I: Female, intestinal contents showing oligochaete setae. J: Vagina and uterus. (Scale bars: A, F, H = 50 µm; B, C, D, G, I = 10 µm; E = 20 µm; J = 100 µm.)