Ultrastructure of a new type of sensory ending in Echinostoma revolutum cercaria (Trematoda: Echinostomatidae).

Two pairs of hitherto unknown multiciliate sensory endings have been demonstrated in free-swimming cercariae of Echinostoma revolutum using transmission and scanning electron microscopy. This type of receptor consists of a bundle of 36--40 short, conically projecting cilia ensheathed by a collar formed by a circular evagination of tegument in shape of a cup. The cilia projecting from the centre of a widened nerve fibre, filled with electron-lucid vesicles, possess a well developed basal body and do not contain a ciliary rootlet. The function of this receptor is discussed.