Key to Families of ASCARIDOIDEA

1 Oesophagus comprising a preventriculus and an oblong to globular ventriculus with one dorsal and one ventral longitudinal suture-like depression, or with small globular ventriculus from which arises a posteriorly directed appendix with such depressions or rarely two appendices; excretory system asymmetrical, confined to left lateral chord; excretory pore situated between base of subventral lips or near nerve ring; intestinal caecum present or absent. Parasitic in mammals, birds, reptiles and fishes............................................................................................ Anisakidae

- Oesophagus without ventriculus or with globular to ellipsoidal ventriculus without longitudinal sutures; excretory system symmetrical, the right lateral canal of which may be somewhat reduced; excretory pore near nerve ring; intestinal caecum present or absent; lips small, semicircular, not offset from anterior end; each lip provided on inner surface with two pairs of small pointed teeth, a continuous dentigerous ridge or two separate transverse dentigerous ridges; interlabia absent; oesophagus with ventriculus; intestinal caecum absent. Parasitic in elasmobranch fishes............................. Acanthocheilidae