Measurements

All measurements are presented in table 1.

Table 1. Morphometrics of Aporcella femina sp. n. from Nigeria and two other African species of the genus.

Measurements in μm except L in mm, and in the form average ± standard deviation (range).

^a 1: Botha & Heyns (Reference Botha and Heyns1990); 2: De Bruin & Heyns (Reference De Bruin and Heyns1992).

^b Calculated from other morphometrics.

Description

Female. Moderately to slender (a = 28–38) nematodes of large size, 3.21–3.64 mm long. Body cylindrical, tapering towards both ends but substantially towards the anterior region, while the tail is short and rounded. Upon fixation, habitus regularly curved ventrad, C- to G-shaped. Cuticle two-layered, very thick throughout the entire body, 4–7 μm in anterior region, 7.5–9.5 μm at mid-body and 7.5–11.5 μm on tail, consisting of a thin outer layer with nearly smooth surface, and a thicker inner layer that displays a fine but distinct transverse striation (fig. 2g). Lateral chords narrow, 6–17 μm wide or 6–19% of mid-body diameter. Ventral and dorsal pores restricted to cervical region, two or three in number at each side at odontostyle–odontophore level; lateral pores small. Lip region offset by a distinct constriction, 3.3–3.8 times wider than high and less than one-third (22–29%) of body diameter at neck base; lips separate, with moderately protruding papillae. Amphidial fovea stirrup-shaped, its opening 9–10.5 μm, less than one-half (38–46%) of lip region diameter. Cheilostom broad, 10.5–14 μm long, with thick walls. Odontostyle strong, 3.8–4.3 times longer than wide, barely shorter (0.9–1.0 times) than lip region diameter and 0.58–0.73% of total body length, with aperture 13–17 μm long or c. two-thirds (58–76%) of total length. Guiding ring simple but distinct, plicate. Odontophore linear, rod-like, 1.9–2.4 times longer than odontostyle. Pharynx entirely muscular, enlarging very gradually, with its basal expansion 5.8–9.0 times as long as wide, 3.1–4.5 times the body diameter at neck base and occupying 52–56% of total neck length; pharyngeal gland nuclei located as follows (n = 1): DO = 47–52, DN = 48–56, DO-DN = 3–5, S₁N₁ = 61–66, S₁N₂ = 73–75, S₂N = 85–88. Cardia short and rounded conoid, 21–32 × 20–34 μm, surrounded by intestinal tissue that forms a short extension projection into the intestinal lumen. Genital system didelphic–amphidelphic, with well-developed genital branches, the anterior 346–565 μm or 11–15% of body length, the posterior 381–638 μm or 12–18% of body length. Ovaries comparatively small, mostly not reaching the oviduct–uterus junction, the anterior 103–259 μm and posterior 106–231 μm long. Anterior oviduct 127–200 μm or 1.4–1.8 body diameters long, posterior oviduct 133–203 μm or 1.4–1.9 body diameters long, both consisting of a slender distal portion made of prismatic cells and a distinct pars dilatata with perceptible lumen. Oviduct and uterus separated by a distinct sphincter. Anterior uterus 191–325 μm or 1.9–3.1 body diameters long, posterior uterus 204–350 μm or 2.1–3.3 body diameters long, often appearing as a simple, tube-like structure, but with some (well-preserved) specimens having a longer uterus, which enables the appreciation of a wider proximal uterine region and a more slender distal region, both of about similar length. No uterine egg observed. Vagina extending inwards 40–54 μm, occupying c. one-half (41–45%) of body diameter: pars proximalis 28–41 × 19–28 μm, with distally convergent walls and surrounded by a relatively weak musculature; pars distalis well-developed, 10–14 μm long; pars refringens absent. Vulva a slightly posterior transverse slit. Prerectum 2.4–4.0, rectum 0.8–1.5 times the anal body diameter long. Tail short, convex conoid, its ventral side weakly straighter than the dorsal side; caudal pores two pairs, close together, at the posterior half of tail, one lateral, another sublateral.

Male. Unknown. Females do not contain sperm cells.

Type locality and habitat

South-west Nigeria, Odeda (7°10′59.999″N, 3°26′42.01″E), an agrarian locality with a history of cassava (Manihot esculenta Crantz) and vegetable production; specimens were collected from a field cultivated with watermelon (Citrullus lanatus) on sandy-loam soil (sand = 66%, silt = 13%, clay = 21%, organic matter = 11.18%, pH 6.22).

Molecular characterization

After sequencing and editing, two totally (100%) identical sequences per each locus (SSU and LSU) were obtained; therefore, only one sequence was used for analysis and deposited into the NCBI GenBank: a 745 bp-long LSU sequence (accession number MW237838) and another 855 bp-long SSU sequence (accession number MW237832). The evolutionary relationships of the new species are presented in figs 3 and 4.

Fig. 4. Bayesian tree with 50% majority rule of Aporcella femina n. sp. from Nigeria using partial LSU (D2–D3) rDNA sequences under the GTR + I + G model. The sequence of new species is indicated by bold font. Scale bar shows the number of substitutions per site.

Type material

Female holotype and nine female paratypes, deposited in the nematode collection of the University of Jaén, Spain.

Etymology

The specific epithet is a Latin term meaning woman or female, and refers to the existence of only females in this species.

Diagnosis and relationships

The new species is characterized by its 3.21–3.64 mm-long body, inner cuticle layer with fine but distinct transverse striation, lip region offset by deep constriction and 22–25 μm broad, odontostyle 20–26 μm at its dorsal side and 19–24 μm at its ventral side, neck 661–811 μm long, pharyngeal expansion 349–451 μm long or 52–56% of total neck length, female genital system didelphic–amphidelphic, uterus 191–350 μm or 1.9–3.3 body diameters long, V = 52–57, tail short and convex conoid (35–48 μm, c = 72–98, c′ = 0.7–0.9) and males absent.

In having a comparatively long body (more than 3.0 mm long), Aporcella femina sp. n. resembles Aporcella magna Andrássy, 2012 and Aporcella pseudospiralis (Botha & Heyns, Reference Botha and Heyns1990) Andrássy, 2012, and significantly differs from its other congeners (body 3.21–3.64 vs up to 3.08 mm long) (see compendium by Álvarez-Ortega et al., Reference Álvarez-Ortega, Subbotin and Peña-Santiago2013 and Vazifeh et al., Reference Vazifeh, Niknam, Naghavi, Jabbari and Peña-Santiago2020). It can be distinguished from A. magna, a species occurring in Chile, in its smaller general size: body 3.21–3.64 versus 4.48–5.00 mm long, n = 5; neck 661–811 versus 888–1020 μm long; tail 35–48 versus 50–60 μm. It is also smaller than A. pseudospiralis, which is only known to occur in South Africa, with a smaller general size (body 3.21–3.64 vs 3.64–4.42 mm long, n = 4; neck 661–811 vs 810–880 μm long), shorter prerectum (122–203 vs 219–280 μm) and female tail (35–48 vs 57–68 μm, c = 72–98 vs 58–73, c′ = 0.61–0.94 vs 0.93–1.15) and male absent (vs present).

Among the small-sized Aporcella species (body up to 3.08 mm long), and due to the comparatively long odontostyle (>16 μm), short (c′ up to 1.1) and convex conoid tail, it is similar to Aporcella papillata (Bastian, 1865) Álvarez-Ortega, Subbotin & Peña-Santiago, 2013 and A. parapapillata (Botha & Heyns, Reference Botha and Heyns1990) Andrássy, 2009. The new species differs from A. papillata, currently recorded from UK only (Thorne & Swanger, Reference Thorne and Swanger1936; Álvarez-Ortega & Peña-Santiago, Reference Álvarez-Ortega and Peña-Santiago2010), in its larger general size (body 3.21–3.64 vs 2.43–3.08 mm long; neck 661–811 vs 510–650 μm long), longer uterus (191–350 vs 111–131 μm or 1.9–3.3 vs 1.3–1.5 body diameters long), more posterior vulva (V = 52–57 vs V = 45–50, n = 11) and male absent (vs present); and from A. parapapillata, recorded from South Africa (Botha & Heyns, Reference Botha and Heyns1990; De Bruin & Heyns, Reference De Bruin and Heyns1992), in its larger general size (body 3.21–3.64 vs 2.11–2.79 mm long; neck 661–811 vs 555–649 μm long), much longer odontophore (44–50 vs 26–38 μm, n = 12) and male absent (vs as frequent as female).

The new species described herein displays intermediate morphometrics between two South African species – namely, A. parapapillata and A. pseudospiralis – all of them described based on relatively few specimens. Aporcella femina sp. n. is very similar to A. pseudospiralis, but, as mentioned above, they differ in their overall size and especially in tail length. Therefore, the possibility of co-specificity could be raised, and the noted differences possibly due to geographical variations. The absence of molecular data for A. parapapillata and A. pseudospiralis currently prevents any molecular comparison, which, when available, would clarify any ambiguity. However, the available morphological information clearly distinguishes the three species from each other, supporting a separate status for them.

The evolutionary relations of the new species, as derived from the molecular analyses based on the partial sequence of SSU and LSU rDNA, are represented in figs 3 and 4. According to the SSU phylogeny, the new species is in a highly supported (BPP: 97%) sister relation with Aporcella vitrinus. Furthermore, Bayesian tree using partial LSU sequence shows that the new species forms part of a fully supported (BPP: 100%) subclade with Aporcella charidemiensis and A. vitrinus, the former being the closest relative, which is recorded from Spain. A highly supported (BPP: 94%) Aporcella clade is made of this subclade along with three Aporcella sequences belonging to A. simplex. Therefore, the present results confirm previous findings (for instance, see Naghavi et al., Reference Naghavi, Niknam, Vazifeh and Peña-Santiago2019; Vazifeh et al., Reference Vazifeh, Niknam, Naghavi, Jabbari and Peña-Santiago2020) about both the monophyly of Aporcella, and the belonging of Aporcella sequences to a large clade morphologically characterized by the absence of pars refringens vaginae, which also includes discolaims in the tree provided herein.