PHILASTERIDES-DICENTRARCHI, N-SP, (CILIOPHORA, SCUTICOCILIATIDA), A HISTOPHAGOUS OPPORTUNISTIC PARASITE OF DICENTRARCHUS-LABRAX (LINNAEUS, 1758), A REARED MARINE FISH

In sea bass Dicentrarchus labrax (L.) reared in the Mediterranean sea, mortality suddenly arose. The diseased fishes, noticeable when almost dead, were massively infested with a histophagous ciliate. Depending on the infected host organs, the ciliate showed in its food vacuoles v arious categories of ingested cells: erythrocytes, ovocytes, and other s. The infecting mode of this presumed ''parasite'' is still unknown, all experimental infections having failed. Morphological, biometric an d ultrastructural studies lead to the conclusion that, because of its morphological characteristics and its main stomatogenesis processes, t his ciliate is a Scuticociliatida Philasterina. Compared to other know n species, it differs by its small size, the small and regular number of its somatic kineties, the position of its buccal organelles (and, m ainly, the bipartite paroral membrane), the presence of two types of e xtrusomes, and a perinuclear envelope. All these characteristics justi fy the creation of a new species: Philasterides dicentrarchi. This par ticular ciliate habitat is compared to that of other commensal or oppo rtunistic parasitic ciliates of invertebrates and marine fishes.