Mediterranean myxozoans: those litle strangers

Trabajo presentado en el XV Simpósio Ibérico de Estudos de Biologia Marinha, celebrado en Funchal, Madeira (Portugal), del 9 al 13 de septiembre de 2008Myxozoans are microscopic metazoans that are mainly fish parasites in both fresh and marine environments. In spite of being discovered 150 years ago, major advances in their knowledge began with the development of aquaculture. Thus, their heteroxenous life cycle (which includes an invertebrate host) was not discovered until 1984 when Wolf & Markiw were studying the life cycle of Myxobolus cerebralis, the causative agent of whirling disease in salmonid fry. The Phylum Myxozoa comprises the class Myxosporea, and the recently described class Malacosporea, which includes Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), responsible for great losses in cultured and wild salmonids in Europe and North America. Although more than 2180 species have been described until now, little is known about the development and life cycle of non-freshwater species. In fact, only one out of the 25 life cycles described so far belongs to a marine myxozoan. Furthermore, the taxonomy and phylogenetic position of this group of organisms are highly controversial. Thus, the most recent studies based on phylogenetic analyses of multiple protein-coding genes have concluded that the taxon Myxozoa should be placed within the phylum Cnidaria, and no longer within Bilateria. In the last 15 years, the number of reports on new myxozoan species parasitizing Mediterranean commercial fish has increased, seemingly because of the development of marine aquaculture and the expanding interest in marine sciences. The aim of the present communication is thus, to offer a wide vision of Mediterranean myxozoan biodiversity, including recent findings and major enigmas that still remain unsolved