Pebrilla paguri (Ciliophora, Folliculinidae) on four Mediterranean hermit crab species

Abstract

The present research aims at broadening the range of possible Pebrilla paguri hosts, by analysing various Mediterranean hermit crab species, as well as at investigating their preferential distribution on the crustacean body. For each crab carrying P. paguri on its exoskeleton, the position and number of the ciliate's loricae were recorded and mapped. Pebrilla paguri loricae were observed only on 16.6% of the hermit crabs examined, with a greater number being observed on Calcinus tubularis and Paguristes eremita, compared to the two other crab species. A reason for this may be that the former are not very active in feeding, motion, and interaction. The highest frequency of P. paguri was observed on the abdomen, telson, and uropods, whereas only a few were found on the cephalotorax. This localisation is discussed in relation to the epibiont's preference for parts of the crab's body that are normally kept deep inside the molluscan shell and characterised by scarce water flow and illumination. These conditions will promote bacterial proliferation and accumulation of the organic residuals, which will become available for P. paguri as food. The preferential distribution of ciliates on the left side of the crab's body can be seen as a way to avoid damage by rubbing against the shell's columella.