Willinema, Baqri and Jairajpuri, 1967

Vazifeh, Nasir, Niknam, Gholamreza, Jabbari, Habibeh, Fallahi, Amin, Zahedi, Ebrahim & Peña-Santiago, Reyes, 2022, Description of Willinema persicum sp. n. (Dorylaimida: Thornenematidae) from Iran, with an updated taxonomy of the genus, Journal of Natural History 56 (13 - 16), pp. 849-863 : 858-861

About the genus Willinema

As mentioned in the introductory section, no relevant, new information about the genus Willinema was available throughout the last three decades, and some discrepancies are found in the papers that appeared in the 1980s ( Carbonell and Coomans, 1985; Andrássy 1986, 1987). Thus, the description of a new species is a remarkable novelty and an opportunity to address the taxonomy of the group.

Diagnosis (after Carbonell and Coomans, emended)

Thornenematidae , Willinematinae. Small- to medium sized nematodes, 0.38–1.89 mm long. Lip region continuous or offset by depression or constriction, lacking any sclerotisation. Odontostyle typical dorylaimid. Guiding ring simple. Odontophore rod-like, with no specialisation. Pharynx enlarging gradually, the basal expansion occupying one-third to one-half of the total neck length. Female genital system mono-opistho-ovarian, often didelphic as the anterior branch appears variably developed, sometimes nearly complete but reduced and not functional, vagina with distinct pars refringens, and transverse vulva. Tail similar in the two sexes, short and rounded; convex-conoid to cylindrical. Male with dorylaimid spicules, and 2–9 widely spaced ventromedian supplements with hiatus.

Type species

W. parvum ( Williams, 1959) Baqri and Jairajpuri 1967

= Labronema parvum Williams, 1959

= Thornenema parvum ( Williams, 1959) Williams 1964

Other valid species

W. brunetti ( Meyl, 1953) Andrássy 1986

= Dorylaimus brunetti Meyl, 1953

= Eudorylaimus brunetti ( Meyl, 1953) Andrassy, 1959

W. chilense sp. nov.

= Eudorylaimus brunettii apud Andrássy (1967) , nec Meyl (1953)

W. eburnense Carbonell and Coomans, 1984

W. laopagense Carbonell and Coomans, 1984

W. nanum Carbonell and Coomans, 1984

W. opisthodelphus ( Thorne and Swanger, 1936) Andrássy 1986

= Dorylaimus opisthodelphus Thorne and Swanger, 1936

= Eudorylaimus opisthodelphus ( Thorne and Swanger, 1936) Andrássy 1959

W. paraparvum Carbonell and Coomans, 1984

W. persicum sp. nov.

Species inquirenda

W. sulphasae ( Tulaganov, 1949) Andrássy 1986

= Dorylaimus sulphasae Tulaganov, 1949

= Eudorylaimus sulphasae ( Tulaganov, 1949) Andrássy 1959

Key to species identification

1a– Smaller general size, body length under 0.7 mm, neck under 170 µm long .............. 2

1b– Larger general size, body length over 0.8mm, neck over 200 µm long, very occasionally slightly shorter .............................................................................................................................. 4

2a– Anterior genital branch reduced to a 25–46 µm long uterine sac ...................... nanum

2b– Anterior genital branch totally absent ........................................................................................ 3

3a– Body 0.38–0.49 mm long, more anterior vulva (V = 39–45) .............................. brunettiae

3b– Body 0.62–0.70 mm long, more posterior vulva (V = 52–54) ................ chilense sp. nov.

4a– Body more than 1.00 mm long, anterior genital branch more than 120 µm long, spicules more than 35 µm long ..................................................................................................... 5

4b– Body up to 1.00 mm long, anterior genital branch up to 113 µm long, spicules in males (if male present) up to 35 µm long ................................................................................. 7

5a– Body 1.427–1.89 mm long, odontostyle 14–18 µm long, 7–9 ventromedian supplements ........................................................................................................................ persicum sp. nov.

5b– Body 1.14–1.33 mm long, odontostyle up to 12.5 µm long, if male present, 4–6 ventromedian supplements present ............................................................................................ 6

6a– Anterior genital branch totally absent, relatively longer caudal region (c = 45, c’ = 1.4) ........................................................................................................................................... opisthodelphus

6b– Anterior genital branch nearly complete but not functional, relatively shorter caudal region (c = 48–62, c’ = 0.8–1.0) .................................................................................. paraparvum

7a– Odontostyle 16–16.5 µm long, neck 249–271 µm long .......................................... parvum

7b– Odontostyle up to 14 µm long, neck up to 226 µm long ................................................... 7

8a– More posterior vulva (V = 48–51), anterior genital branch 45–113 µm, male as frequent as female ............................................................................................................ eburnense

8b– More anterior vulva (V = 45–47), anterior genital branch 18–21 µm, male unknown ................................................................................................................................................ laopangense

Table 2 provides a compendium of the main morphometrics of Willinema species.

Comments on some species

E. brunettiae : A species repeatedly recorded in Italy ( Meyl 1953, 1954), Ivory Coast ( Andrássy 1956; Jacobs 1984), Hungary ( Andrássy 1958), Venezuela ( Loof 1964; Dao 1970), Chile ( Andrássy 1967), and Moldova ( Bushmakiu et al. 2000; Poiras 2008). Its original description was quite simple, but Andrássy (1956) provided some addditional information and better illustrations that fitted those of the type material (see Table 2 ). Nevertheless, Andrássy (1967) studied a Chilean population that significantly differed from the previous ones in several remarkable features: larger general size (body 0.62– 0.70 vs 0.38–0.39 mm long in original and other populations), more slender body (a = 33–35 vs a = 22–30), and much more posterior vulva (V = 52–54 vs V = 39–45). This material is also easily distinguishable from the other small species of the genus, W. nanum , with shorter body (0.45–0.52 mm) too, as this species bears a distinct, 25– 45 µm long, anterior uterine sac that is nearly absent in Chilean specimens. Taking into consideration that these specimens were well characterised morphologically and are sharply separable from their relatives, they are regarded as belonging to a different species, herein named W. chilense sp. nov.

E. opisthodelphus: Only known to occur in its type locality in the USA, Utha, where Thorne and Swanger (1936) found it associated with sod in a mountain summit. The original description is poor in detail, but sufficient to distinguish it from other members of the genus. It is provisionally retained as a valid species. Popovici (1968) studied several Romanian females identified as Eudorylaimus opisthodelphus , but the true identity of this material cannot be confirmed, although it is certainly not conspecific with the American ones as their general size is much larger (body 1.9–2.06 vs 1.3 mm, respectively) and the vulva much more posterior (V = 49–50.5 vs V = 42).

E. sulphasae : The true identity of this species remain obscure. Its original (and only available) description by Tulaganov (1949) is very poor in detail and raises reasonable doubts about the nature of some relevant traits. Thus, the female genital system was originally described as being diovarian, with a very anterior vulva position (V = 35), an exceptional combination in dorylaimid taxa where a very anterior vulva is always associated with the reduction of the anterior genital branch. Actually, Andrássy (1987, p. 306) was aware of this apparent inconsistency and stated that the species should be regarded as mono-opistho-ovarian, justifying its transference to Willinema . Some other features of W. sulphasae , in particular its small size and its subcylindrical tail (c’ = 1.5) with a terminal hyaline layer, resemble the pattern observed in some members of the genus Tylencholaimellus Cobb in Cobb, 1915, but the pharyngeal expansion occupies about one-half of the total neck length (vs very short, bulb-like in Tylencholaimellus representatives). Therefore, the species is herein considered a species inquirenda.

Notes on its phylogeny

Willinema is a dorylaimid genus whose evolutionary affinities have not been elucidated yet. Leaving aside some general traits (odontostyle relatively strong, typical dorylaimoid pharynx), two morphological features were especially relevant to address its classification, namely the short and rounded tail of both sexes, and its monoopistho-ovarian female genital system. In a revision of the family Thornenematidae, Andrássy (1987) created the subfamily Willinematinae to accommodate Willinema and Sclerolabia (see above), both rounded-tailed and mono-opistho-ovarian genera that differ in the absence and presence, respectively, of labial and postlabial sclerotisations. In their evaluation of the taxonomical status of the family Thornenematidae, Coomans and Carbonell (1988) concluded that only three thornenematid genera should be grouped under a subfamilar (rather than familiar) taxon, Thornenematinae; meanwhile, they considered the relationships of other genera, Willinema among them, uncertain, although they should be evaluated within a ‘wider concept of the family Dorylaimidae’ (p. 384).

The new Iranian species herein described perfectly fits the known morphological pattern of Willinema representatives and confirms the two most relevant synapomorphies of the genus, namely the rounded tail in both sexes and the monoopistho-ovarian condition of the female genital system. The rounded tail is a remarkable trait shared with members of the subfamily Labronematinae Peña-Santiago and Álvarez-Ortega, 2014 in Dorylaimidae . Actually, Willinema species much resemble the members of the genus Crassolabium , if we accept the diovarian condition of the latter, a relevant difference indeed since mono-ovarian species do not occur within the components of the family Dorylaimidae as hitherto defined. It is unfortunate that the authors failed in their attempt to sequence the new species herein described, as molecular analyses will certainly provide new insights into the phylogeny of Willinema .