The organ's development through the lineage can be estimated by comparing groups that branched early, such as the velvet worm and horseshoe crab to the advanced eye condition found in insects and other derived arthropods.
Several animal groups studied in Australia consist largely of short-range endemics, including freshwater and terrestrial Gastropods (snails and slugs), earthworms, velvet worms, mygalomorph spiders, schizomids, millipedes, phreatoicidean crustaceans, and freshwater crayfish.