Oleaxonchium olearum, Peña-Santiago & García-Ruiz & Ruiz-Cuenca & Abolafia, 2024

Peña-Santiago, Reyes, García-Ruiz, Miriam, Ruiz-Cuenca, Alba N. & Abolafia, Joaquín, 2024, Oleaxonchium olearum gen. et sp. nov. (Nematoda, Dorylaimida) associated with an olive grove in the southern Iberian Peninsula, and new insights into the evolutionary relationships within Belondiridae, Zoosystematics and Evolution 100 (3), pp. 1029-1039 : 1029-1039

Oleaxonchium olearum gen. et sp. nov.

Figs 1 , 2 , 3 , 4

Material examined.

Twelve females from one location are in good condition for preservation.

Morphometrics.

See Table 1 .

Description.

Female. Very slender and medium-sized nematodes. Body cylindrical, conspicuously tapering towards the anterior end, much less so towards the posterior one as the tail is short and rounded. Upon fixation, habitus curved ventrad to a more or less open C shape. Cuticle smooth, two-layered, 0.5–1 µm thick at anterior region, 2.5–4 µm in mid-body, and 8–11 µm on tail, consisting of a thinner outer layer and a much thicker inner layer bearing radial striation, especially appreciable at caudal region. Large cervical lacunae are present. Lateral chord very narrow, 4–10 µm wide, occupying up to one-fifth (9–21 %) of midbody diameter, bearing abundant elliptical gland bodies, more perceptible at posterior body region. Lateral pores button-like, when observed with SEM. Lip region almost rectangular in lateral view, visibly narrower than the adjoining body, 1.8–2.1 times wider than high, and ca one-sixth (15–17 %) of body diameter at neck base, its anterior and lateral margins sclerotized and somewhat refractive, with hardly visible labial and cephalic papillae. SEM observations: lip region almost octogonal when observed in face view, with totally fused lips; its margin slightly elevated, marking off a somewhat sunken area; oral field comparatively small as inner labial papillae are almost equidistant between the oral aperture and the marging, far from the outer labial papillae; labial papillae button-like, delimited by a small circular incisure, with a distinct pore at their center, cephallic papillae unusually simple, small pore-like. Amphid fovea cup-like, its aperture 6.5–7.5 µm long, almost equal (0.9–1.1 times) to the lip region width. Cheilostom a truncate cone 11.5–12 µm long, 1.6–1.7 times as long as the lip region width, with thin walls that distinctly thicken at its anterior (perioral) end. Odontostyle slightly fusiform, 5–7 times as long as wide, longer (1.3–1.5 times) than lip region width, 0.35–0.42 % of body length, its aperture 2–3 µm or less than one-third (20–30 %) of total length. Guiding ring simple, distinct. Odontophore rod-like, 1.4–1.6 times the odontostyle, bearing very weak thickenings at its base. Pharynx very long, consisting of a slender anterior region, a very short narrower (isthmus-like) intermediate section, and a large, strongly muscular posterior expansion 18–38 times as long as wide, 10–15 times longer than body diameter at neck base, which occupies ca two-thirds (63–72 %) of the total neck length, and appears enveloped by a strong spiral muscular sheath with almost strait bands; gland nuclei obscure in the specimens examined. Nerve ring situated at 147–178 µm, or 17–22 % of the total neck length from the anterior end. Pharyngo-intestinal junction consisting of a cylindrical, tongue-like, 20–27 × 6.5–11 µm cardia, almost totally surrounded by intestinal tissue. Genital system mono-opistho-ovarian, didelphic: anterior branch reduced, 102–165 µm long or 4–6 % of body length, consisting of a tube-like uterus, a narrowing, probably a very weak sphincter, and a distal cell mass 20–24 µm long, certainly representing a vestigial oviduct and / or ovary; posterior branch well-developed, 190–303 µm long or 8–11 % of body length, with a variably large ovary 56–146 µm long, often not reaching the sphincter, bearing oocytes first in several rows and then in a single row, oviduct 72–116 µm long or 1.6–2.6 body diameters that consists of a slender distal region made of prismatic cells and a proximal pars dilatata with visible lumen inside, sphincter present but not especially distinct between oviduct and uterus, uterus 87–122 µm long or 1.9–2.6 body diameters (its length however should be taken with caution as it always appears convoluted), tripartite as it consists of a longer proximal region with wider lumen, a shorter intermediate section that bears refractive elements (Z-like structure), and a dilate, almost spherical, distal part. Vagina 22–27 µm long, extending inwards to often more than one-half (48–60 %) of body diameter: pars proximalis 11–16 × 8–17 µm and encircled by moderately developed musculature, pars distalis 9–12 µm long. Vulva a transverse slit ca 10 µm long. Prerectum 9.6–12.2, rectum 0.9–1.1 anal body diameters long. Anus a visibly arched transverse slit ca 4 µm long. Caudal region short and rounded, its inner core reaching 61–77 % of tail length, caudal pores two pairs, sublateral, at the middle of tail.

Male. Unknown.

Molecular characterization.

After sequencing and editing, ten sequences of type specimens were obtained for phylogenetic analyses. Six 18 S rDNA sequences, which were 1653, 1696, 1705, and 1709 (three sequences) bp length (acc. PP 956610 – PP 956615, respectively), presented 1651 bp in common, and a Blast search showed that they were 98.97 % similar to those of Axonchium sp. (acc. MG 921264 and OQ 946544). Four 28 S rDNA sequences, which were 728, 739, 742, and 745 bp length (acc. PP 956616 – PP 956619, respectively), presented 720 bp in common, and a Blast search showed that they were 93.34 % similar to those of Metaxonchium giennense (acc. OQ 473053 – OQ 473054), 91.14 % to those of Metaxonchium magnum (OQ 099691, OQ 099693), and 88.86 % to that of Axonchium sp. ( ON 927906 ).

Diagnosis.

The new species is characterised by its 2.44–2.87 mm long body, lip region 7–7.5 µm wide, odontostyle 10–10.5 µm long, neck 723–973 µm long, pharyngeal expansion occupying 63–72 % of the total neck length, female genital system mono-opistho-ovarian, didelphic, with anterior branch occupying 4–6 % of body length, posterior uterus 87–122 µm long or 1.9–2.6 body diameters and tripartite, with a short intermediate section bearing refractive elements, vulva ( V = 58–61) a transverse slit, caudal region short and rounded (29–35 µm, c = 74–89, c ’ = 0.9–1.1), and male unknown.

Type locality and habitat.

Spain, Málaga province, Antequera municipality, “ La Capilla ” farm (37.198283, - 4.543868, elevation 491 m), where the new species was collected in an olive grove with intensive tillage.

Type material.

Female holotype and nine female paratypes were deposited in the nematode collection of the University of Jaén, Spain . Two female paratypes were deposited with the United States Department of Agriculture Nematode Collection (USDANC) at Beltsville, MD, USA .

Etymology.

The species epithet is the Latin term olearum = belonging to or corresponding to olives, as type material was found in an olive grove.

Figures

Figure 1. Oleaxonchium olearum gen. et sp. nov. (female). A. Entire; B-D. Anterior body region in lateral median (B, C) and lateral surface (D) views; E. Neck region; F. Isthmus-like narrowing between both pharyngeal sections; G. Vagina; H. Genital system; I. Oviduct-uterus junction; J. Pharyngo-intestinal junction; K, L. Caudal region; M. Detail of uterine Z-like sructure Scale bars: 200 µm (A); 5 µm (B – D, G, M); 100 µm (E); 10 µm (F, I – L). 50 µm (H).

Figure 2. Oleaxonchium olearum gen. et sp. nov. (female, general morphology, LM). A. Neck region; B. Entire; C, D, F, I. Anterior body region in lateral median (C, D, F) and lateral surface (I) views; E. Isthmus-like narrowing between both pharyngeal sections; G. Posterior body region; H. Pharyngo-intestinal junction; J. Gland-like bodies at the lateral chord. Scale bars: 100 µm (A); 200 µm (B); 5 µm (C, D, F, I); 50 µm (G); 10 µm (E, H, J).

Figure 3. Oleaxonchium olearum gen. et sp. nov. (female, genital system, and caudal region, LM). A. Genital system; B. Anterior genital branch; C. Oviduct-uterus junction; D, E. Vagina; F, G. Rectum and caudal region; H. Detail of uterine Z-like structure. Scale bars: 50 µm (A, B); 10 µm (C, F, G); 5 µm (D, E, H).

Figure 4. Oleaxonchium olearum gen. et sp. nov. (female, SEM). A-C. Lip region, in face view; D. Lateral pores; E. Anterior body region, lateral view; F. Anterior body region, ventral view; G. Caudal region, sublateral view; H. Vulva, ventral view. Scale bars: 1 µm (A-C); 5 µm (D); 2 µm (E, F); 4 µm (G, H).