Distribution of Udonella caligorum Johnston, 1835 (Monogenea: Udonellidae) on Caligus elongatus Nordmann, 1832 (Copepoda: Caligidae)

Abstract

A large number (2933) of Caligus elongatus (Copepoda: Caligidae) removed from the buccal cavities of cod, Gadus morhua, off the west coast of Scotland, were examined for presence and distribution of Udonella caligorum (Monogenea: Udonellidae). Distribution of worms was not consonant with space available for attachment. Eggs and young worms were found primarily on the posterior half of the copepod, whereas adults occupied predominantly the lateral margins of the cephalothoracic shield. It was concluded that U. caligorum has a feeding area and a nursery area on the copepod and carries out migrations between them. Location of the feeding area strongly suggests that the worm feeds directly on the epithelial tissues of the fish.