Acrolichanus auriculatus (Digenea, Allocreadiidae): distribution of sensory papillae, musculature and FMRFamide-like immunoreactivity in adult worms

The muscle system and the FMRFamide immunopositive components of the nervous system of flatworms Acrolichanus auriculatus (Digenea, Allocreadiidae), an intestine parasite of acipenserid fishes, were studied for the first time by immunocytochemical, histochemical methods and confocal laser scanning microscopy. Scanning electron microscopy in A. auriculatus revealed a consistent pattern in the number and arrangement of ciliated and unciliated sensory papillae along the digenean body. Morphological data demonstrated the presence of the circular, longitudinal and diagonal muscles in different body regions of A. auriculatus. The musculature of the oral and ventral suckers, the digestive system, as well as the muscles extending radially from the genital pore are described. The study revealed the presence of the FMRFamide immunopositive staining in the central and peripheral nervous systems of A. auriculatus: in the neurons and neurites of the brain, brain commissure, in three pairs of the longitudinal nerve cords and commissures. FMRFamide immunopositive nerve elements innervate the attachment organs and the compartments of the digestive, reproductive and excretory systems.