The Bryozoan genus Adeonella has a broad, though disjunct, distribution in the southern hemisphere. The type species, A. platalea, is widespread in the western Pacific and the eastern Indian Oceans. It is a morphologically variable species in which zooidal polymorphism
is highly developed. There are relatively few other species of Adeonella in the Indo-West-Pacific region. By contrast, the western Indian Ocean fauna comprises a substantial number of species; degrees of polymorphism vary greatly between these species and the fauna includes a number
of forms in which polymorphic features are at a minimum. The fossil record is meager and Tertiary representatives of the genus seem to be confined to European horizons; the Atlantic-Mediterranean species A. polystomella is common in Miocene and Pliocene deposits of southern Europe.
The striking contrast between the Adeonella faunas of the Indo-West-Pacific region and the South African region of the western Indian Ocean seems to reflect different evolutionary histories.
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