Aporcelaimoides minor, 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 : 5-9

Taxon classification Animalia Dorylaimida Aporcelaimidae

Aporcelaimoides minor sp. n. Figs 5, 6, 7

Material examined.

Ten females from three localities, in good state of preservation.

Measurements.

See Table 2.

Description.

Female. Moderately slender to slender nematodes of medium size, 2.09-2.61 mm long. Body cylindrical, distinctly tapering towards the anterior end, less so towards the posterior one as the caudal region is very short and rounded to truncate. Habitus regularly curved ventrad after fixation, often spiral-shaped. Cuticle three-layered, especially distinguishable at caudal region: 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 3.0-4.5 µm at anterior region, 4.5-6.5 µm in mid-body and 6.5-9.5 µm on tail. Lateral chord 7-13 µm wide at mid-body, occupying one-tenth to less than one-sixth (9-15%) of mid-body diameter. Two ventral and two 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, 2.8-3.3 times as wide as high and one-fifth to less than one-third (21-30%) of body diameter at neck base; lips mostly amalgamated, somewhat angular; papillae perceptible, somewhat protruding. Amphid fovea cup-shaped, its opening occupying 8-10 µm or up to one-half (44-50%) of lip region diameter. Cheilostom nearly cylindrical, lacking any differentiation. Mural odontostyle attached subventrally, 6.7-7.7 times as long as wide, 0.7-0.9 times as long as lip region diameter, and 0.54-0.72% of body length; aperture 11-13 µm long or up to six-sevenths (73-84%) its length. Guiding ring simple, somewhat plicate, at 0.6-0.8 lip region diameters from anterior end. Odontophore linear, rod-like, irregular at its base, in lateral view with the ventral side longer that the dorsal one (figure 7A, C), and 2.0-2.4 times the mural odontostyle length. Anterior region of pharynx enlarging very gradually; basal expansion 8-12 times as long as wide, 4.1-5.3 times as long as body diameter and occupying 57-66% of total neck length; gland nuclei obscure in most specimens examined, DN = 54 (n=1) and S2N = 92 (n=1). Nerve ring located at 158-177 µm from anterior end or 24-31% of total neck length. Cardia rounded conoid, 11-19 × 14-18 µm; a ring-like structure is present surrounding its junction to pharyngeal base. Genital system didelphic-amphidelphic, with both branches almost equally and well developed, the anterior 174-207 µm long or 7-9% of body length and the posterior 168-220 µm long or 7-9% of body length. Ovaries variably sized, the anterior 93-191 µm, the posterior 84-175 µm long; oocytes arranged first in two or more rows, then in a single row. Oviduct 73-103 µm long or 0.9-1.1 times the corresponding body diameter, and consisting of a slender part with prismatic cells and a weakly developed pars dilatata. Oviduct-uterus junction marked by a sphincter. Uterus a short, simple, tube-like structure 44-69 µm long or 0.5-0.9 times the corresponding body diameter, lacking sperm cells inside. Vagina extending inwards 38-51 µm or two-fifths to one-half (43-53%) of body diameter: pars proximalis 25-35 × 15-20 µm, with somewhat sigmoid walls and surrounded by weak musculature; pars refringens with two small, triangular to drop-shaped pieces measuring 8-10 × 6-8 µm and with a combined width of 14-19 µm; and pars distalis short, 3.0-5.5 µm long. Vulva a transverse slit. Prerectum 1.4-2.1, rectum 0.8-1.1 anal body diameters long. Tail very short and rounded to truncate. Caudal pores two pairs, one sublateral, another sub-dorsal.

Male. Unknown.

Diagnosis.

The new species is characterized by its body 2.09-2.61 mm long, lip region offset by deep constriction and 19-20 µm broad, mural odontostyle 14-16 µm long at its ventral side with aperture occupying 73-84% of its length, neck 579-649 µm long, pharyngeal expansion 331-423 µm long or occupying 57-66% of total neck length, uterus a simple tube and 44-69 µm long or less than (0.5-0.9 times) the corresponding body diameter, pars refringens vaginae well developed, V = 48-56, female tail very short and rounded to truncate (14-26 µm, c = 90-146, c’ = 0.3-0.6), and male unknown.

Relationships.

This species resembles Aporcelaimoides haguei comb. n. in having relatively small mural odontostyle (up to 17 µm long) and pars refringens vaginae present. It can be, however, easily distinguished from this in its smaller general size (L = 2.09-2.61, neck 579-649 µm long vsL = 4.67-5.42, neck 1112-1178 µm long), less slender body (a = 23-33 vsa = 52-62), the absence (vs presence) of rows of minute denticles on stomatal wall), and its much shorter female tail (14-26 µm, c’ = 0.3-0.6 vs 46-47 µm, c’ = 0.7).

Besides, in having short mural odontostyle (11-14 µm at its ventral side) the new species resembles Aporcelaimoides brevistylum sp. n. and Aporcelaimoides californicum , but it differs from these in its well developed pars refringens vaginae (vs absent). Moreover, it differs from Aporcelaimoides brevistylum sp. n. in its shorter neck (579-649 vs 663-767 µm), wider lip region (19-20 vs 17-18 µm), smaller mural odontostyle aperture (occupying 73-84% vs 62-71% its length), shorter female tail (14-26 µm, c = 90-146, c’ = 0.3-0.6 vs 35-46 µm, c = 58-76, c’ = 0.6-0.8), and male absent (vs present). And from Aporcelaimoides californicum in its shorter (L = 2.09-2.61 vsL = 5.53) and less slender (a = 23-33 vsa = 75) body, larger mural odontostyle aperture (occupying 73-84% vs one-half of its length), shorter uterus (44-69 µm long or less than one body diameter vs about 430 µm long or about 5.3 times the corresponding body diameter), and shorter female tail (14-26 µm, c’ = 0.3-0.6 vs 44 µm, c’ = 1.0).

Type locality and habitat.

Vietnam, Bac Giang Province, Tay Yen Tu Natural Reserve, collected from soil in a pristine tropical forest, in July 2008.

Other localities and habitats.

Vietnam, Cao Bang Province, Cao Bang Natural Reserve (GPS coordinates: 22°34'07"N and 105°52'34"), in a tropical evergreen forest soil in association with Dipterocarpus sp. and Cinnamomum sp., collected in 2013. Dak Lak province, Chu Yang Sin National Park, in October 2012.

Type material.

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

Etymology.

The specific epithet means ‘small’ and refers to the comparatively small general size of the new species.

Remarks.

In spite of it was collected from three localities, the material examined is very similar in its main morphological features and morphometrics. Nevertheless, some differences have been also observed, especially affecting the female tail shape as some specimens show a short and rounded-conoid caudal region whereas it becomes extremely short and truncate in other individuals.