Evolution of Life Cycles and Phylogeny of Trematodes

Abstract

Evolution of Trematoda as a separate taxon of high level is still obscure. This is mainly due to the fact that although there are abundant publications devoted to this group of parasitic flatworms our knowledge about them is still insufficient. Trematode life cycles are studied in detail only in several model species. Unfortunately, many taxa of family level and higher are known only from total mounts of mature maritae. Our understanding of trematode morphology is therefore limited: most descriptions of the structure of sexually mature individuals of the hermaphroditic generation contain only an analysis of the topography of the main organs — the suckers, the digestive and reproductive system. Data on the structure of the excretory, nervous and muscular systems and the secretory apparatus of maritae are scarce and have been obtained from few species. Reproductively mature individuals of the trematode hermaphroditic generation are more poorly studied than turbellarians. Comparative morphology of the larvae of the hermaphroditic generation, cercariae and metacercariae, and the parthenogenetic generations, sporocysts and rediae, has not been investigated using the methodological approaches of modern evolutionary morphology.