Labial sense organs of the nematode, Heterakis gallinarum.

The labial sense organs of Heterakis gallinarum (Schrank 1788) were examined by scanning and transmission electron microscopy. Two large doublet papillae are visible externally on the dorsal lip while a single doublet papilla, a short peglike ventrolateral papilla, and the opening of the amphid are visible on each subventral lip. Internal anatomy of these papillae indicates that the doublet papillae are probably pressure receptors while the ventrolateral papillae may be combined mechano- and chemoreceptors. Amphids resemble the structure of amphids of several previously studied nematodes. Six internal labial receptors, two at the inner edge of each lip, can be identified by transmission microscopy. They may be mechanoreceptors recording cuticular stresses during feeding. Each sense organ is associated with a complexly folded system of membranes delimiting extracellular space continuous with space surrounding the dendritic process of the receptor.