Sylphodorylaimus sylphoides ( Williams, 1959 ) Nasir & Gholamreza & Faegheh & Abootalebi, 2024

Nasir, Reyes Peña-Santiago, Gholamreza, Nasir Vazifeh, Faegheh, Gholamreza Niknam & Abootalebi, Faegheh, 2024, New insights into the evolutionary relationships of Opisthodorylaimus sylphoides (Williams, 1959), with proposal of Sylphodorylaimus n. gen. (Nematoda, Dorylaimida, Thornenematidae), Zoosystema 46 (15), pp. 349-359 : 351-356

Sylphodorylaimus sylphoides ( Williams, 1959) n. comb.

( Figs 1-3 ; Tables 1 ; 2 )

Dorylaimus sylphoides Williams, 1959: 21 .

Thornenema sylphoides – Andrássy 1960: 6. — Eliava 1984: 35 (catalogued).

Opisthodorylaimus sylphoides – Carbonell & Coomans 1986: 391 (re-description). — Andrássy 2009: 247 (catalogued). — Peña-Santiago 2021: 432 (catalogued).

MATERIAL EXAMINED. — Iran • 7♀, 1♂; Mazandaran province, Zirab County; 36°10’68”N, 052°57’86”E; 500 m a.s.l.; rhizosphere of Diospyros lotus L., UTANC • 6♀, 2♂; East-Azarbaijan province, Sufiyan, Roodghat area , Zeinabad village ; 38°29’53”N, 46°12’38”E; 1600 m a.s.l.; in the rhizosphere of black cherry trees ( Prunus cerasus L.); UJANC .

MORPHOLOGICAL DESCRIPTION

Adult

Very slender (a = 34-54) nematodes of medium size, 1.95- 2.42 mm long. Body cylindrical, tapering towards both ends but more so posteriorly, the tail being long and filiform in both sexes. Upon fixation, habitus very slightly curved ventrad. Cuticle smooth under light microscope, 1-1.5 Μm thick in anterior region, 2 Μm at mid-body and 5-6 Μm on dorsal side of tail, two-layered, consisting of a thin outer layer with constant thickness throughout the body, and a thicker inner layer, especially distinct at caudal region. Lateral chord 7-12 Μm or 16-24% of mid-body diameter. Lip region continuous with the adjoining body, somewhat truncate anteriorly, 2.0-2.3 times as wide as high and c. one-fourth (23-26%) of body diameter at neck base, with totally amalgamated lips and not protruding (labial and cephalic) papillae. Amphid fovea cup-like, its aperture 6 Μm, occupying c. one-half (55%) of lip region diameter. Cheilostom with moderately thick walls visibly arched inward. Odontostyle typical dorylaimid, 5.7- 7.3 times longer than wide, somewhat longer (1.1-1.3 times) than lip region diameter, and 0.59-0.66% of body length; aperture 4.5-6 Μm or 33-42% of its length. Guiding ring double. Odontophore rod-like, 1.5-1.7 times longer than odontostyle. Conspicuous lacunae are present at both sides of anterior body region. Pharynx entirely muscular, gradually enlarging into the basal expansion that is 6.3-8.9 times longer than wide, 3.2-4.5 times the body diameter at neck base, and occupies less than one-half (42-47%) of the total neck length; gland nuclei located as follows: DO = 56-59, DN = 59-62, S 1 N 1 =68-71, S 1 N 2 =76-79, S 2 N=86-87. Nerve ring situated at 128-139 Μm or 31-36% of the total neck length from the anterior end. Pharyngo-intestinal junction consisting of a short and rounded cardia surrounded by intestinal tissue, all together forming a 10.5-16.5 × 9-12.5 Μm structure bulging into intestinal lumen.

Female

Genital system mono-opistho-ovarian, with anterior branch reduced to a vestigial uterine sac 6.5-17.5 Μm long, less than one-half of body diameter. Posterior branch well developed, 180-243 Μm long, occupying 8-10% of body length. Ovary variably long, 77-154 Μm, with oocytes first in two or more rows, then in a single row. Oviduct 89-121 Μm or 1.9-2.4 body diameters long, consisting of slender portion made of prismatic cells and a moderately developed pars dilatata with visible lumen. Uterus a simple tube-like structure, 71-84 Μm or 1.5-1.8 body diameters long. Vagina extending inwards 22-26 Μm to c. one-half (46-57%) of body diameter: pars proximalis 12-15.5 × 14-18 Μm, with slightly arched walls encircled by very weak musculature; pars refringens hardly perceptible, with (in lateral view) two small 5 × 2 Μm, weakly sclerotized pieces with a combined width of 10-11 Μm; pars distalis 4-5 Μm long. Vulva a very anterior, c. 4 Μm long, somewhat rectangular, longitudinal opening. Prerectum 1.8-5.8, rectum 1.1-1.4 anal body diameters long. Tail long and filiform with acute tip, first tapering more abruptly until about one body diameter behind the anus, then very gradually, inner core extending to 69-75% of total length, so with a visible terminal hyaline portion, caudal pores two pairs, one sublateral, another subdorsal, at the middle of the wider portion of tail.

Male

Prerectum 5.7, cloaca 1.6 times the body diameter at level of cloacal aperture long. Genital system diorchic, with opposite testes. In addition to the ad-cloacal pair, located at 8.5 Μm from the cloacal aperture, presence of a series of 9-11, shortly spaced, 7-11 Μm apart, ventromedian supplements, the most posterior of them located at 68 Μm from the ad-cloacal pair, in front of the level of spicule anterior end, thus with a long hiatus. Spicule dorylaimid, curved ventrad, 4.7 times longer than wide, 1.6 times the body diameter at cloacal aperture; head 4 Μm or 10% of spicule length, 1.1 times as long as wide, with its dorsal side visibly longer than the ventral one and curved; median piece occupying 59% of spicule width; posterior end 3.5 Μm; ventral hump located at 13 Μm or 32% from the spicule anterior end; curvature 129°. Lateral guiding piece 10.5 Μm long, relatively coarse, 3.5 times longer than wide, and visibly bifurcate at the end. Tail similar to that of female.

REMARKS

Morphologically, the material examined is very homogeneous, with no relevant difference observed. Morphometrically, it is very similar too, but Sufiyan females display slightly smaller general size than Zirab ones (body 1.95-2.22 vs 2.16- 2.42 mm long, respectively) and are less slender (a= 34-44 vs a =43-54), both always within the known ranges of the species (see below).

Taking the Carbonell & Coomans’ (1986) description as reference for comparative purposes, the Iranian females herein examined are identical to type and other European and Iraqi populations studied by these authors, with similar lip region, pharynx, female genital system and caudal region. Nevertheless, the vulva was described ( Carbonell & Coomans 1986: 391) as circular, but the ventral view ( Fig. 2K ) suggests that it is a short, somewhat rectangular longitudinal opening, a difference that is difficult to appreciate when the specimens are observed, as usual, in lateral view.

Morphometrically, the species displays remarkable intraspecific variability affecting most relevant measurements and ratios (compiled in Table 2 ), the body (1.66-2.48 mm) and tail lengths (350-550 Μm,c=3.5-5.9, c’=14-24) showing especially wide ranges whereas other relevant traits as lip region width (9-14 Μm), odontostyle length (12-20 Μm) or vulva position ( V =34-38) present less variation. When different populations are compared, the ranges of their morphometrics are congruent or largely overlap in general, therefore these populations have been regarded as conspecific and their small differences as geographical variations ( Carbonell & Coomans 1986).

MOLECULAR CHARACTERISATION

After sequencing and editing, one 28S rDNA gene partial sequence (accession OQ550280) c. 800 bp in length was obtained. This sequence was compared with those available from GenBank. Upon BLAST search, it shows high similarity (98-99% identity, three indels/no gap) with sequences ( AY 593008-AY593010) of European specimens of the same species. Molecular analyses ( Fig. 4 ), also confirmed the identity of the Iranian specimens. Thus, the available sequence forms a maximally supported clade (P = 93%) with other sequences obtained from European nematodes ( Holterman et al. 2008).

Figures

FIG. 1. — Sylphodorylaimus syphoides (Williams, 1958) n. comb. (Zirab population, male): A, caudal region; B, entire; C, D, anterior region, lateral median view; E, anterior region, lateral surface view; F, lateral guiding piece; G, H, posterior body region, in part; I, spicule. Scale bars: A, H, 50 µm; B, 500 µm; C, I, 10 µm; D-F, 5 µm; G, 20 µm.

FIG. 2. — Sylphodorylaimus syphoides (Williams, 1958) n. comb. (Zirab population): A, female, entire; B, male, entire; C-E, anterior region, lateral median view; F, pharyngo-intestinal junction; G, oviduct-uterus junction; H, anterior region, lateral surface view; I, female, caudal region; J, male, caudal region; K, vulva, ventral view; L, P, vagina region; M, lateral guiding piece; N, male, posterior body region in part; O, spicule. Scale bars: A, B, 500 µm; C, D, N, O, 10 µm; E, H, K, L, M, P, 5 µm; F, G, 20 µm; I, J, 50 µm.

FIG. 3. — Sylphodorylaimus sylphoides (Williams,1959) n. comb. (Sufiyan population): A, female, anterior region in lateral median view; B, male, anterior region in median ventral view; C, female, entire; D, male, entire; E, anterior region, lateral surface view; F, pharyngo-intestinal junction; G, vagina region; H, female,caudal region; I, male, caudal region; J, sperm cells; K, spicule; L, ventromedian supplements. Scale bars: A, B, E-G, J-L, 10 μm; C, D, 100 μm; H, I, 50 μm.

FIG. 4. — Phylogenetic relationships of Sylphodorylaimus sylphoides (Williams,1959) n. comb. Bayesian 50% majority rule consensus tree as inferred from D2-D3 expansion segments of 28S rDNA sequence alignments under the GTR + G + I model. Posterior probabilities are given for appropriate clades. Newly obtained sequence is indicated by bold letter.