Xennellidae De Coninck, 1965

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 : 9

Family Xennellidae De Coninck, 1965

Diagnosis (emended from Lorenzen 1981)

Cuticle annulated except in X. cephalata Cobb, 1920 where it is apparently smooth; longitudinal ridges on cuticle usually present. Amphideal fovea pocket-shaped, horseshoe-shaped or circular. Anterior sensilla arranged in a 6 +6+ 4 pattern; long, setose outer labial and cephalic sensilla of similar length. Tapering cephalic capsule present ( Xennella ) or absent ( Porocoma ); when present, cephalic capsule offset from rest of body by constriction, cuticular discontinuity and/or thickened cuticle. Buccal cavity minute, tubular, without teeth. Female reproductive system monodelphic ( Xennella ) or didelphic ( Porocoma ). Male reproductive system monorchic (at least in Xennella suecica Allgén, 1935 ); spicules short, arcuate; gubernaculum present or absent, precloacal supplements present or absent.

Type genus

Xennella Cobb, 1920 .

Remarks

De Coninck (1965) erected the subfamily Xennellinae , which originally only contained the genus Xennella . He placed the subfamily within the family Dasynemellidae De Coninck, 1965 , order Desmodorida De Coninck, 1965 . The subfamily was later raised to family by Gerlach & Riemann (1973 /1974). The Xennellidae was placed within the Trefusiida by Lorenzen (1981) based on the pocket-shaped amphid and absence of metanemes. This classification was followed by De Ley & Blaxter (2004).

Within the Enoplida , an annulated cuticle is found in the genus Cricohalalaimus Bussau, 1993 ( Oxystominidae , suborder Ironina Siddiqi, 1983 ), and the Lauratonematidae (suborder Trefusiina ) are characterized by a “distinctly striated” cuticle. A cephalic capsule is present only within the suborder Enoplina , which is formed by the muscles of the anterior end of the pharynx attaching to the body cuticle. In Xennella , there is no evidence of any attachment between the pharynx and the body cuticle; instead, the cephalic capsule appears to be formed solely by the thickening of the cuticle. This would suggest that this genus may be better placed within one of the marine chromadorean orders, instead of within the Enoplida . It is possible that the placement of Xennella and Porocoma will need to be updated in the future as more morphological and molecular data become available.