Groupe : Cephalic characters
The cephalic extremity of primitive Trichostrongylina are similar to the Strongylida ( in particular, the Cloacininae and Oesophagostominae) in having a buccal capsule, six lips (or more rarely, a corona radiata) and a dorsal oesophageal tooth. The complement of cephalic sense organs is complete, i.e., six internal and six external labial and four cephalic papillae, and two amphids.
In Heligmonellinae, we can observed a separation of the cuticule body and cephalic cuticule in two distinct compartments. They thus present a former end individualized at the head: it is a cephalic vesicle, which transmits mechanical stimulis in direction of the cephalic papillae present around the mouth.
Cephalic characters.