Trefusiidae Gerlach, 1966

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 : 15-16

Family Trefusiidae Gerlach, 1966

Diagnosis (emended from Lorenzen 1981)

Cuticle smooth or faintly striated. Labial region generally divided into three lips. Inner labial sensilla usually papillose, rarely setose, either in separate circle or very close to outer labial sensilla. Outer labial sensilla and cephalic setae usually in separate circles (except Trefusialaimus ); outer labial setae usually jointed, cephalic setae often located far posteriorly, sometimes posterior to amphids. Amphids either spiral or non-spiral (round or pocket-shaped). Buccal cavity without teeth, either minute to medium size, funnel-shaped and not cuticularised, or large, barrel-shaped and cuticularised. Secretory-excretory system restricted to pharyngeal region (often not observed). Spicules short, curved or straight, with or without capitulum; gubernaculum present or absent, without apophyses (except in Africanema ). Female reproductive system monodelphic or didelphic; ovaries reflexed (except in Cytolaimium exile and Trefusialaimus idrisi ). Male reproductive system usually diorchic (monorchic in Trefusialaimus ). Papilliform, setiform or discoid precloacal and pharyngeal supplements may be present. Caudal glands restricted to tail region.

Type genus

Trefusia de Man, 1893 .

Remarks

Gerlach (1966) erected the subfamily Trefusiinae , which he placed within the Oxystominidae and which comprised the genera Trefusia , Rhabdocoma , Cytolaimium and Halanonchus . While there had been general agreement by various authors about the placement of Trefusia with the Oxystominidae ( Filipjev 1934; De Coninck & Schuurmans Stekhoven 1933; Chitwood & Chitwood 1937), the placement of Cytolaimium , Rhabdocoma and Halanonchus was more controversial and relationships had been proposed with the families Monhysteridae de Man, 1876 , Linhomoeidae Filipjev, 1922 and Tripyloididae Filipjev, 1928 ( Filipjev 1934; Chitwood 1936, 1951; Wieser 1956; de Coninck 1965; Riemann 1966). Riemann (1966) noted that although Rhabdocoma and Trefusia share many similarities, they differ in the structure of the female reproductive system (monodelphic in Rhabdocoma and didelphic in Trefusia ); however, he followed the classification of Gerlach (1966). Wieser & Hopper (1967) subsequently moved Rhabdocoma , Cytolaimium and Halanonchus into the freshly erected subfamily Halanonchinae , which they placed within the family Tripyloididae . They justified this change based on the large buccal cavity (in Halanonchus ), the spiral amphids (in Cytolaimium and Rhabdocoma ) and the presence of jointed setae (all three genera). They also argued that the presence of deeply incised lips, a trait also found in some Tripyloididae , indicates relationships with Tripyloididae . This argument appears to be mostly based on their observations of deeply incised lips in Halanonchus macrurus Cobb, 1920 ; however, we argue that they have misinterpreted the presence of a cuticular discontinuity in the buccal cavity as deeply incised lips (see below). It is not clear why Trefusia was not also moved to the Halanonchinae as it is very similar to Rhabdocoma and Cytolaimium except for features of the reproductive system. Gerlach & Riemann (1973 /74) modified the classification of Wieser & Hopper (1967) by bringing the Halanonchinae together with the Trefusiinae and raising the latter to family status. They also moved Cytolaimium and Rhabdocoma back to the Trefusiinae , leaving Halanonchus as the sole genus within the Halanonchinae . No reason was given for this change, but it seems likely that the subfamilies were re-organised to reflect differences in the buccal cavity (i.e., small and not cuticularized in Trefusiinae vs large and cuticularized in Halanonchinae ). Trefusialaimus , a genus with a minute buccal cavity, was subsequently described by Riemann (1974) and placed within the Trefusiinae . Vincx & Furstenberg (1988) later described Africanema , a genus with a large cylindrical buccal cavity, which they placed within the Halanonchinae .

Shi & Xu (2017) recently proposed moving Rhabdocoma to the Halanonchinae based on the presence of only one ovary in both Rhabdocoma and Halanonchus , and based on the result of phylogenetic analyses of 18S rDNA sequences. They argue that the structure of the female reproductive system is a more taxonomically informative trait for determining relationships among higher taxa than the buccal cavity.