Trefusiina Siddiqi, 1983

Leduc, Daniel, Zhao, Zeng Qi & Sinniger, Frederic, 2020, Halanonchus scintillatulus sp. nov. from New Zealand and a review of the suborder Trefusiina (Nematoda: Enoplida), European Journal of Taxonomy 661 (661), pp. 1-45 : 6-7

Suborder Trefusiina Siddiqi, 1983

Diagnosis (modified from Smol & Coomans 2006)

Cuticle smooth or striated, except in Xennellidae De Coninck, 1965 where it is annulated. Metanemes absent, except in Trischistomatidae . Amphids usually non-spiral; spiral only in some Trefusiinae Gerlach, 1966 and Halanonchinae Wieser & Hopper, 1967 . Outer labial and cephalic sensilla setiform and usually positioned in two well-separated circles (except in Trefusialaimus , Lauratonematidae and Tripylina ). No cephalic capsule, except in Xennella which has a non-annulated cephalic capsule formed by thickening of body cuticle. Buccal cavity usually without teeth (except in Trischistomatidae and Lauratonematidae ). Opening of pharyngeal glands unknown in most species, near buccal cavity in Trefusialaimus . Male reproductive systems usually with two testes (monorchic in Trefusialaimus

and Trischistomatidae ). Female reproductive system monorchic or diorchic; ovaries reflexed except in Cytolaimium exile Cobb, 1920 and Trefusialaimus idrisi where they are outstretched. Caudal glands (when present) lie completely within the tail or position unknown.

Remarks

Lorenzen (1981) erected the order Trefusiida , which was subsequently the lowered to the level of suborder within the Enoplida in the classification of De Ley & Blaxter (2004) based on analyses of 18S rRNA sequences ( Rusin et al. 2001) and following Siddiqi (1983). The Trefusiida was not considered monophyletic by Lorenzen (1981) because it is not characterized by any character which is apomorphic for that taxon. The order, as defined by Lorenzen (1981), originally comprised the following families: the Simpliconematidae , Xennellidae , Lauratonematidae , Trefusiidae and Onchulidae Andrássy, 1964 . The Onchulidae , which is comprised of terrestrial and freshwater species but no marine species, has since been moved to the order Triplonchida Cobb, 1920 in the classification of De Ley & Blaxter (2002; 2004). The Onchulidae is characterised by spicules surrounded by a muscular pouch (or ‘capsule’), a trait which differentiates the Triplonchida from the Enoplida ( De Ley & Blaxter 2002) .

The family Simpliconematidae comprises a single genus with a single species described from a single male specimen. Simpliconema aenigmatoides Blome & Schrage, 1985 was placed within the Trefusiida by Lorenzen (1981, 1994) based on the presence of three lips, the pharyngeal glands seemingly opening in the frontal part of the pharynx, the absence of metanemes and having secretory-excretory gland located in the pharyngeal region. Lorenzen (1981, 1994), however, also noted similarities with the genus Linhystera Juario, 1974 , family Xyalidae Chitwood, 1951 , order Monhysterida Filipjev, 1929 , in the arrangement of cephalic sensilla, amphid shape, location of secretory-excretory gland and single anterior testis to the left of the intestine.

The family Xennellidae comprises two genera, Xennella Cobb, 1920 and Porocoma Cobb, 1920 , comprising four and one species, respectively. This group is unusual in having a cephalic capsule ( Xennella ) and an annulated cuticle with longitudinal ridges (both genera) but is similar to most Trefusiina in having outer labial and cephalic setae in separate circles and pocket-shaped amphideal fovea, as well as lacking metanemes ( Lorenzen 1981).

The family Lauratonematidae comprises three genera ( Lauratonema , Lauratonemella Tchesunov, 1984 and Lauratonemoides De Coninck, 1965 , together comprising 13 species) which differ in the structure of the male copulatory apparatus and/or female reproductive system. The Lauratonematidae differ from most other Trefusiina taxa (except Tripylina and Trefusialaimus ) in having the outer labial setae and cephalic setae in a single circle. The family is also characterized by unique features within the Enoplida , i.e., vulva either very close to anus or with female genital branch joining the cloaca, presence of only one posterior testis in some species, and ovary always to the left of the intestine and posterior testis always to the right of the intestine ( Lorenzen 1981). The placement of this group in the SSU phylogenetic tree indicates no relationship with the Trefusiina ; instead it appears to be closely related to Anoplostoma (see Fig. 1 ). However, due to the weak support for this placement, we leave the Lauratonematidae within the Trefusiina until more conclusive evidence for an alternative classification is provided.

The family Trischistomatidae comprises two genera: Tripylina with 22 valid species and Trischistoma with 17 valid species. Phylogenies based on SSU sequences consistently show that Trischistoma and Tripylina form a monophyletic clade with the Trefusiidae , which, along with morphological similarities discussed below, strongly indicate that the Trischistomatidae should be included in the Trefusiina .

The family Trefusiidae comprises two subfamilies, six genera ( Africanema , Cytolaimium Cobb, 1920 , Halanonchus Cobb, 1920 , Rhabdocoma , Trefusia and Trefusialaimus ) and 34 valid species. It is characterised mainly by plesiomorphic traits (i.e., jointed outer labial sensilla, buccal cavity without teeth) and was considered not monophyletic by Lorenzen (1981). However, Vincx & Vanreusel (1989) considered the presence of the ventral gland in the pharyngeal region as an apomorphic character for the Trefusiidae within the Trefusiina .

Figures

Fig. 1. Bayesian tree of the Enoplida (and Triplonchida outgroup) inferred from SSU sequences, aligned using the MUSCLE alignment algorithm and with regions of questionable alignment removed using Gblocks, under the general time-reversible (GTR) + proportion of invariable sites (I) + gamma distribution (G) model. Trefusiina sequences are shown in underlined font, and new Trefusialaimus sequences are highlighted in grey. The five enoplid clades described by Bik et al. (2010) are identified on the right. Posterior probability (left) and bootstrap values (right) are given on corresponding clades. Dashes (-) indicate no support and aserisks (*) indicate <50% support. The scale stands for substitutions per site.