Molecular phylogeny of Mesometridae (Trematoda, Digenea) with its relationto morphological changes in parasites

Complete ITS (Internal Transcribed Spacer) ribosomal DNA sequences were obt ained for the six species know at present time within the Mesometridae Poch e, 1926. The adult stages are intestinal parasites of herbivorous sparid te leosts. Aligned sequences were analysed with Maximum Parsimony, Maximum Lik elihood and Neighbor-Joining phylogenetic methods to infer evolutionary rel ationships among mesometrid species. The ITS based phylogeny obtained showe d the two Wardula species as a sister group to other Mesometridae, and as c ompared to morphological data, suggest some general tendencies in the morph ological evolution of this group. It consists mainly in changes from elonga ted to subcircular forms, regression of the pharynx, and the development of a strong accessory attachment organ.