Aspects on the Ultrastructure of the Cephalic Region in Two Species of Acrobelinae (Nematoda,Cephalobidae)

The lip structures termed labial probolae, characteristic for the subfamily Acrobelinae, and the anterior sense organs have been studied by electron microscopy. The labial probolae consist of an amorphous tissue with denser strengthenings. They do not contain any sensory structures or musculature. The anterior sense organs consists of: (1) six inner labial sensilla, each with one receptor ending in a pore on a papilla; (2) six outer labial sensilla, each with one receptor ending in the cuticle; (3) four cephalic sensilla, each with two receptors, one ending in a pore on a papilla and the other in the cuticle; (4) two amphids, each with 12 sensory neurons basally; (5) accessory sensilla ventro-laterally. The combination of several chemoreceptive anterior sensilla and the morphological diversity of the labial probolae within the subfamily may aid in the utilization of different soil microhabitats.