Noddies are members of the tern family Sternidae in the genera Anous, Procelsterna, and Gygis. They are a tropical group, characterised by the notch-wedge shaped (not forked) tail; coastal and pelagic oceanic. Studies of mtDNA sequences (Bridge, 2005) have shown that the noddies are at least 2 groups that split off early from the ancestral terns at different points of time; the relationships of Procelsterna were not researched for lack of samples. It seems to represent either a third lineage linking the noddies and the marsh terns, or is closely related to Gygis.