Taxonomy, host-specificity and biogeography of Symmetrovesicula Yamaguti, 1938 (Digenea: Fellodistomidae) from chaetodontids (Teleostei: Perciformes) in the tropical Indo-west Pacific region.

Combined molecular and morphological data demonstrate the presence of two species of Symmetrovesicula Yamaguti, 1938 in chaetodontid fishes from Australian waters. A total of 2,462 individuals of 46 species of chaetodontid at eight localities were dissected. Analysis of the rDNA ITS2 revealed the presence of three genotypes, two separated by a single base difference and the third differed from the other two by 10-11 base differences. Subsequent morphological examination identified a number of variations that supported the presence of two species; however, we found no additional evidence to support the presence of a third species corresponding to the single base variation. Thus, we take the conservative approach of recognising two species of Symmetrovesicula within Australian waters, S. chaetodontis Yamaguti, 1938 from off Ningaloo Reef, Western Australia and S. gracilis n. sp. from off Ningaloo Reef, the Great Barrier Reef, Queensland and New Caledonia. Both species exhibit distinct restrictions to certain clades of chaetodontids.