Diagnosis (from Blome & Schrage 1985)
Cuticle striated. Labial region divided into three lips. Cephalic sensilla with 6+10 arrangement; setose outer labial and cephalic sensilla. Circular amphideal fovea. Male reproductive system monorchic with anterior testis to the left of the intestine; sperm cell drop-shaped. Spicules slender, elongated; gubernaculum absent. Tail filiform. Females not known.
Simpliconema Blome & Schrage, 1985.
Simpliconema is characterized by cephalic and caudal regions similar to those of Marisalbinema Tchesunov, 1990 (family Xyalidae; Fig. 2), which was described after the treatment of the Trefusiida by Lorenzen (1981, 1994), while the long slender spicules are similar to those of Paramonohystera Steiner, 1916 (Xyalidae). More broadly, Simpliconema is characterized by features which resemble the Monhysterida more closely than the Trefusiina, including a circular amphideal fovea (within the Trefusiina, the amphideal fovea is circular only in some Trefusiidae genera, namely species of Cytolaimium, Trefusia, and Rhabdocoma), 6+10 arrangement of the anterior sensilla (usually 6+6 + 4 in the Trefusiina, except in the Lauratonematidae, Trefusialaimus and Tripylina), and the presence of only one anterior testis (usually two testes in Trefusiina, except some Lauratonematidae, Trefusialaimus, and Trischistomatidae). Blome & Schrage (1985) also noted differences with the Trefusiidae, such as the structure of the sperm (drop-shaped vs elongated in the Trefusiidae) and differentiated vas deferens (vs undifferentiated in the Trefusiidae). It appears likely that the taxonomic placement of the Simpliconematidae will need to be updated. Morphological information on the structure of the female reproductive system should allow us to settle the placement of this genus.