Xyalidae Chitwood, 1951

Leduc, Daniel, 2015, One new genus and five new nematode species (Monhysterida, Xyalidae) from Tonga and Kermadec Trenches, Southwest Pacific, Zootaxa 3964 (5), pp. 501-525 : 502-503

Family Xyalidae Chitwood, 1951

Diagnosis ( Coomans & Eyualem-Abebe (2006)): Cuticle striated or annulated. Six outer labial setae and four cephalic setae in one circle, with cephalic setae shorter than or equal to labial setae. Often additional cephalic setae and occasionally eight groups of sub-cephalic setae are present. Stoma usually funnel-shaped, completely or only at the base surrounded by pharyngeal tissue. Ventral gland mostly absent (or invisible under light microscopy). Females with one (anterior) ovary to the left side of intestine. Males usually with two testes, the anterior one to the left side of intestine, the posterior one (may be absent) to the right side.

Remarks. The holophyly of the Xyalidae within the Order Monhysterida was established based on the placement of the gonads relative to the intestine; with very few exceptions, the anterior gonad is always situated to the left, and posterior gonad to the right of the intestine ( Lorenzen 1981).

The genus Macramphis Timm, 1961 , later renamed Megalamphis by De Coninck (1965), was originally classified with the family Sphaerolaimidae by Timm (1961), but classified with the family Xyalidae by Lorenzen (1981). Fonseca & Bezerra (2014) and Venekey et al. (2014) placed Megalamphis with the Sphaerolaimidae , but did not provide explanations for this placement.