Some biological controls on the distribution of shallow water sea stars ( Asteroidea; Echinodermata) ( Valvatida).

Tropical shallow water sea star faunas, especially those of the Indo-West Pacific, are dominated by the order Valvatida. Among sea stars, valvatidans have the best-developed antipredatory devices. The Valvatida includes few genera that prey on active, solitary invertebrates, but such habits are common in other orders, and cooler water. Protective structures appear to restrict predatory abilities. The importance of sea stars as predators on solitary organisms declines in tropical latitudes, yet sea stars have evolved only limited basic structural variation since their appearance in the Ordovician. Phylogenetic constraints in adaptability appear strong in sea stars because of their evolutionary failure to maintain predatory life habits in shallow tropical waters.-from Author