Aporcelaimoides brevistylum, 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 : 2-5

Taxon classification Animalia Dorylaimida Aporcelaimidae

Aporcelaimoides brevistylum sp. n. Figs 1, 2, 3, 4 A–E

Material examined.

Twelve females and fourteen males from two localities, in variable state of preservation.

Measurements.

See Table 1.

Description.

Adult. Moderately slender to slender nematodes of medium size, 1.95-2.90 mm long. Body cylindrical, distinctly tapering towards the anterior end, less so towards the posterior one because the caudal region is rounded. Habitus regularly (often strongly) curved ventrad after fixation, usually spiral-shaped. Cuticle three-layered, especially distinguishable at caudal region, where it consists of thinner outer layer bearing very fine transverse striation through the entire body, thicker intermediate layer with radial striation and thin inner layer; thickness 3-5 µm at anterior region, 4-7 µm in mid-body and 9.0-12.5 µm on tail. Lateral chord 8-20 µm wide at mid-body, occupying one-eighth to less than one-fifth (12-18%) of mid-body diameter. Three ventral and three dorsal body pores are usually present at level of mural odontostyle-odontophore, their corresponding ducts appearing especially thickened beneath intermediate cuticle layer. Lip region offset by deep constriction, 2.7-3.3 times as wide as high and one-fifth to two-sevenths (18-30%) of body diameter at neck base; lips (under SEM) amalgamated; labial papillae button-like, very perceptible and protruding under LM, surrounded by a ring-like annulus (occasionally two annuli), the inner ones at the margin of oral field; cephalic papillae larger than the labial ones, with an oval transverse slit; oral aperture a dorso-ventral, slightly hexagonal orifice, the lip region hence showing a biradial symmetry. Amphid fovea cup-shaped, its opening occupying 9-11 µm or one-half to two-thirds (52-64%) of lip region diameter. Cheilostom nearly cylindrical, lacking any differentiation. Mural odontostyle attached subventrally and comparatively short, 4.1-5.4 times as long as wide, 0.6-0.8 times as long as lip region diameter, and 0.43-0.61% of body length; aperture 8-9 µm long or up to five-sevenths (62-71%) its length. Guiding ring simple, somewhat plicate, at 0.6-0.8 lip region diameters from anterior end. Odontophore linear, rod-like, 3.4-4.2 times the mural odontostyle length. Anterior region of pharynx enlarging very gradually; basal expansion 9.5-12.6 times as long as wide, 4.6-7.2 times as long as body diameter, and occupying 58-66% of total neck length; gland nuclei obscure in most specimens examined, DN = 50 (n=1) and S2N = 84 (n=1). Nerve ring located at 154-185 µm from anterior end or 21-26% of total neck length. Cardia rounded conoid, 10-14 × 14-18 µm; a ring-like structure is present surrounding its junction to pharyngeal base. Tail short and rounded; inner core with irregular shape 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 207-254 µm long or 9-10% of body length and the posterior 233-300 µm long or 9-13% of body length. Ovaries moderately sized, usually not surpassing the sphincter level, the anterior 95-365 µm, the posterior 106-316 µm long; oocytes arranged first in two or more rows, then in a single row. Oviduct 96-124 µm long or 1.0-1.4 times the corresponding body diameter, and consisting of a slender part with prismatic cells and a well developed pars dilatata bearing wide lumen that often containing sperm cells inside. Oviduct-uterus junction marked by a sphincter. Uterus a short, simple, tube-like structure 85-182 µm long or 1.0-2.1 times the corresponding body diameter, most specimens with abundant sperm cells inside. Uterine eggs ovoid, 153 (n=1) × 79, 85 (n=2) µm, 1.8 (n=1) times as long as wide. Vagina extending inwards 43-57 µm or four-ninths to two-thirds (45-65%) of body diameter: pars proximalis 32-44 × 28-34 µm, with somewhat sigmoid walls and surrounded by weak musculature; pars refringens absent; and pars distalis well developed, 11-14 µm long. Vulva a post-equatorial transverse slit. Prerectum 1.8-2.6, rectum 1.0-1.2 anal body diameters long.

Male. Genital system diorchic, with opposite testes. In addition to the ad-cloacal pair, situated at 15-20 µm from cloacal aperture, there is only one ventromedian supplement located out the range of spicules, at 48, 58 (n=2) µm from ad-cloacal pair. Spicules distinctly robust and massive, especially in its posterior half, 3.4-4.6 times its maximum width, 1.2-1.7 times the body diameter at level of the cloacal aperture: dorsal contour regularly convex, ventral contour very weakly concave, with shallow or weak hump and hollow; curvature 126-142°; head occupying 7-21% of spicule total length, its dorsal contour conspicuously curved at its anterior end and longer than the ventral one, which is short and straight; median piece 7.2-10.9 times as long as wide, occupying 35-50% of spicule maximum width, reaching the posterior tip; posterior end 5-9 µm wide. Lateral guiding pieces 13-17 µm long, 3.5-5.1 times as long as wide. Prerectum 2.9-4.4, cloaca 1.1-1.3 the corresponding body widths long.

Diagnosis.

The new species is characterized by its body 1.95-2.90 mm long, lip region offset by deep constriction and 17-18 µm broad, ventral side of mural odontostyle 11-14 µm with aperture occupying 62-71% of its length, neck 663-767 µm long, pharyngeal expansion 387-508 µm long or occupying 58-66% of total neck length, uterus a simple tube and 85-182 µm long or 1.0-2.1 times the corresponding body diameter, pars refringens vaginae absent, V = 55-63, female tail short and rounded (35-46 µm, c = 58-76, c’ = 0.6-0.8), male tail similar to that of female (34-42 µm, c = 49-69, c’ = 0.6-0.8), spicules 67-86 µm long, and one ventromedian supplement bearing hiatus.

Relationships.

In having short mural odontostyle (11-14 µm at its ventral side) and pars refringens vaginae absent, the new species is morphologically close to Aporcelaimoides californicum Heyns, 1965 and Aporcelaimoides probulbum Heyns, 1965, but it can be distinguished from both species in its smaller (L = 1.95-2.90 vsL = more than 3) and less slender (a = 25-35 vsa ≥ 41) body. Besides, Aporcelaimoides brevistylum sp. n. differs from Aporcelaimoides californicum in its comparatively longer neck (b = 3.3-3.7 vsb = 7.6), larger mural odontostyle aperture (occupying 62-71% vs one-half of its length), more posterior vulva (V = 55-63 vsV = 51), shorter uterus (85-182 µm or 1.0-2.1 times the corresponding body diameter vs about 430 µm long or about 5.3 times the corresponding body diameter), comparatively shorter female tail (c = 58-76, c’ = 0.6-0.8 vsc = 126, c’ = 1.0), and male present (vs absent). And from Aporcelaimoides probulbum in its shorter neck (663-767 µm, b = 3.3-3.7 vs 883-1011 µm, b = 3.9-5.2), narrower lip region (17-18 vs about 21 µm), and comparatively longer tail (c = 49-76 vsc = 75-127).

Moreover, in having short mural odontostyle (11-14 µm at its ventral side) the new species resembles Aporcelaimoides haguei (Hunt, 1978), comb. n., but it differs in its smaller general size (L = 1.95-2.90 and neck 663-767 µm long vsL = 4.67-5.42 and neck 1172-1178 µm long), less slender body (a = 25-35 vsa = 52-62), absence (vs presence of rows of minute denticles on stomatal wall, indeed a very relevant feature), pars refringens vaginae absent (vs present), comparatively longer female tail (c = 49-76 vsc = 99-118), and male present (vs absent).

Type locality and habitat.

Vietnam, Dak Lak province, Chu Yang Sin National Park, where it was collected from soil of a pristine forest in October 2012.

Other locality and habitat.

Vietnam, Lam Dong Province, Bidoup-Nui Ba National Park, from soil of a pristine forest, collected in June 2013.

Type material.

Female holotype and seven female and nine male paratypes deposited in the nematode collection of the University of Jaén, Spain. One female and one male paratypes deposited in the nematode collection of the Institute of Ecology and Biological Resources, Vietnam.

Etymology.

The specific epithet is a compound Latin term referring to the short mural odontostyle that characterizes this species.

Remarks.

The two populations examined are very similar in their morphological features and morphometrics, but some minor differences have been also noted, which are herein regarded as intraspecific variation. Thus, the population from Dak Lak province shows a shorter mural odontostyle (ventral side 11-13 vs 13-14 µm, dorsal side 13-14 vs 14-17 µm, in females) and comparatively longer neck (b = 3.3-3.4 vsb = 3.5-3.7).