Sense organs of monogenean skin parasites ending in a typical cilium

Abstract

Single receptors seen with the electron microscope to consist of a terminal cilium embedded in a nerve bulb have been found in the skin parasitic monogeneanGyrodactylussp., adult and larvalEntobdella soleae, Leptocotyle minor(adult) and in the endoparasitic juvenile ofAmphibdella flaviolineata.Their distribution inGyrodactylussp. has been mapped using phase-contrast microscopy, and staining with the indoxyl acetate method for non-specific esterases revealed a nervous connexion between the lateral ventral nerve cord and the ‘tangoreceptor’. The general relationships of the nervous system inGyrodactyluswere investigated by staining with the thiocholine method for cholinesterase. The ‘sensory’ neurone contains vesicles, microtubules and mitochondria and the whole nerve bulb is sealed into the epidermis by means of septate desmosomes. The basal body of the cilium is not greatly modified and there is no obvious rootlet system. The terminal cilium of single receptors inEntobdella soleaehas a 9 + 2 structure. A compound sense organ from the head ofEntobdella soleaehas also been described. The significance of the fibre arrangement in the terminal cilia and the possible roles of these sense organs have been discussed.I should like to thank Dr D. L. Lee for training in electron microscope techniques and for his encouragement, Dr P. Tate for his continued interest and the staff of the Marine Biological Laboratory, Plymouth, especially Mr G. Best and Mr J. E. Green, for their assistance. This work was conducted during tenure of a Science Research Council Fellowship and the Tucker-Price Research Fellowship of Girton College.