Aporcelaimoides silvaticum, Alvarez-Ortega, Sergio, Nguyen, Thi Anh Duong, Abolafia, Joaquin, Vu, Thi Thanh Tam & Pena-Santiago, Reyes, 2015

Alvarez-Ortega, Sergio, Nguyen, Thi Anh Duong, Abolafia, Joaquin, Vu, Thi Thanh Tam & Pena-Santiago, Reyes, 2015, Three new species of the genus Aporcelaimoides Heyns, 1965 from Vietnam (Nematoda, Dorylaimida, Aporcelaimidae), with an updated taxonomy of the genus, ZooKeys 516, pp. 1-26 : 10-12

Taxon classification Animalia Dorylaimida Aporcelaimidae

Aporcelaimoides silvaticum sp. n. Figs 4 F–I, 8, 9

Material examined.

Two females and four males, in variable state of preservation.

Measurements.

See Table 2.

Description.

Adult. Moderately slender to slender nematodes of medium size, 2.09-2.60 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, to a more or less open C, occasionally more curved at posterior body region, spiral-shaped in only one male specimen. Cuticle three-layered, especially visible distinct at caudal region, consisting of thin outer layer bearing fine transverse striation through the entire body, a much thicker intermediate layer with radial striation, and a thin inner layer; thickness 2.5-4.0 µm at anterior region, 5-6 µm in mid-body and 8-10 µm on tail. Lateral chord 7-12 µm wide at mid-body, occupying one-tenth to one-eighth (10-12%) of mid-body diameter. Three ventral and three dorsal body pores are usually present at level of odontostyle-odontophore, their corresponding ducts appearing especially thickened beneath inner cuticle layer. Lip region visibly narrower than adjacent body, offset by depression, 2.2-2.6 times as wide as high and one-fifth to one-fourth (19-27%) of body diameter at neck base; lips (under SEM) amalgamated; papillae button-like, the inner labial ones rather close the margin of oral field and surrounded by one or two ring-like annuli, whereas the outer labial ones are surrouned by only one annulus and the cephalic ones lack a such differentiation; oral aperture a dorsoventral, nearly hexagonal orifice, the lip region hence showing a biradial symmetry. Amphid fovea cup-shaped, its opening at level of cephalic depression and occupying 12-13 µm or up to three-fourths (72-75%) of lip region diameter. Cheilostom nearly cylindrical, lacking any differentiation. Mural odontostyle attached subventrally and comparatively short, 4.5-4.9 times as long as wide, 0.6-0.7 times as long as lip region diameter, and 0.44-0.54% of body length; aperture 7-8 µm long or up to two-thirds (60-66%) its length. Guiding ring simple, somewhat plicate, at 0.5-0.7 lip region diameters from anterior end. Odontophore linear, rod-like, 3.8, 4.1 (3.5, 3.7 in males, n=2) times the odontostyle length. Anterior region of pharynx enlarging very gradually; basal expansion 8.3-11.0 times as long as wide, 5.0-5.8 times as long as body diameter, and occupying 58-64% of total neck length; gland nuclei obscure in all the specimens examined. Nerve ring located at 139-169 µm from anterior end or 23-26% of total neck length. Cardia rounded conoid, 10-16 × 12-18 µm; a ring-like structure is present surrounding its junction to pharyngeal base. Tail short, rounded to rounded conoid, its inner core bearing a finger-like projection at tail end. Caudal pores two pairs, one lateral, another sub-lateral.

Female. Genital system didelphic-amphidelphic, with both branches almost equally and well developed, the anterior 246, 387 µm long or 10, 15% of body length and the posterior 301 µm long or 12% (n=1) of body length. Ovaries moderately sized, usually not surpassing the sphincter level, the anterior 82, 119 µm, the posterior 66, 103 µm long; oocytes arranged first in two or more rows, then in a single row. Oviduct 99-107 µm long or 1.2, 1.3 times the corresponding body diameter, and consisting of a slender part with prismatic cells and a moderately developed pars dilatata with visible lumen but no sperm cell. Oviduct-uterus junction marked by a sphincter. Uterus a short, simple, tube-like structure 128-243 µm long or 2.1, 2.8 times the corresponding body diameter, one female containing abundant sperm cells inside. Vagina extending inwards 31, 32 µm or about three-eighths (36%, n=1) of body diameter: pars proximalis 23, 24 × 25, 26 µm, with somewhat sigmoid walls and surrounded by weak musculature; pars refringens with two small, triangular to drop-shaped pieces measuring 5 × 4, 5 µm and with a combined width of 9, 10 µm; and pars distalis 1.0, 1.5 µm long. Vulva a post-equatorial transverse slit. Prerectum 2.3, 2.5, rectum 0.8, 1.2 anal body diameters long.

Male. Genital system diorchic, with opposite testes. In addition to the ad-cloacal pair, situated at 16-19 µm from cloacal aperture, there is a series of two or three widely spaced (22-42 µm apart) ventromedian supplements, the posteriormost of which lying out the range of spicules, but very close to the spicules end, being situated at 42-63 µm from ad-cloacal pair. Spicules relatively robust, 3.5-4.6 times its maximum width, 1.3-1.6 times the body diameter at level of the cloacal aperture: dorsal contour regularly convex, ventral contour bearing weak hump and hollow; curvature 140 –143º; head occupying 8-10% of spicule total length, with both contours nearly straight, and its dorsal side longer than the ventral one; median piece 6.5-8.3 times as long as wide, occupying 45-54% of spicule maximum width, reaching the posterior tip; posterior end 5-6 µm wide. Lateral guiding pieces 19-23 µm long, 6.4-7.8 times as long as wide. Prerectum 3.0-3.3, cloaca 1.2-1.4 times the corresponding body width long.

Diagnosis.

The new species is characterized by its body 2.09-2.60 mm long, lip region offset by depression and 17-18 µm broad, mural odontostyle 11-12 µm long at its ventral side with aperture occupying 60-66% of its length, neck 597-720 µm long, pharyngeal expansion 353-452 µm long or occupying 58-64% of total neck length, uterus a simple tube and 128-243 µm long or 2.1-2.8 times the corresponding body diameter, pars refringens vaginae well developed, V = 58-60, female tail short and rounded to rounded conoid (31-37 µm, c = 69-83, c’ = 0.7), male tail similar to that of female (27-31 µm, c = 67-94, c’ = 0.6-0.7), spicules 64-75 µm long, and two or three widely spaced ventromedian supplements bearing hiatus.

Relationships.

The new species differs from its relatives by its lip region offset by depression (vs constriction). Besides, in having pars refringens vaginae and short mural odontostyle (11-12 µm long at its ventral side), Aporcelaimoides silvaticum sp. n. is morphologically similar to Aporcelaimoides haguei comb. n. and Aporcelaimoides minor sp. n., but it can be distinguished from them in its narrower lip region (17-18 vs equal or 19 µm or more) and more posterior vulva (V = 58-60 vsV up to 57). It also differs from Aporcelaimoides haguei comb. n. in its smaller general size (L = 2.09-2.60, neck 597-720 µm long vsL = 4.67-5.42, neck 1112-1178 µm long), less slender body (a = 28-33 vsa = 52-62), absence (vs presence) of rows of minute denticles on stomatal wall), shorter female tail (31-37 vs 46-47 µm), and male present (vs absent). And from Aporcelaimoides minor sp. n. in its shorter mural odontostyle (11-12 vs 14-16 µm at its ventral side) with smaller aperture (occupying 60-66% vs 73-84% of its length), longer female tail (27-31 µm, c = 67-94, c’ = 0.6-0.7 vs 14-26 µm, c = 90-146, c’ = 0.3-0.6), and male present (vs absent). Finally, the new species also resembles Aporcelaimoides brevistylum sp. n. in having short mural odontostyle, but it differs from this in its well developed (vs absent) pars refringens vaginae and higher number of ventromedian supplements (two or three vs one).

Type locality and habitat.

Northern Vietnam, Cuc Phuong National Park, where the new species was collected from soil of a pristine tropical forest in 2009.

Type material.

Female holotype and one female and three male paratypes, deposited in the nematode collection of the University of Jaen, Spain. One male paratype deposited in the nematode collection of the Institute of Ecology and Biological Resources, Vietnam.

Etymology.

The specific epithet is a Latin term meaning 'from the jungle’, and refers to the habitat where the species dwells.