The affinities and origins of the crown-of-thorns sea starAcanthasterGervais

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Abstract
Comparative morphology of both complete organisms and individual skeletal elements reveal strong similarities between the crown-of-thorns sea star Acanthaster and various members of the Oreasteridae. The monogeneric Acanthasteridae, therefore, is transferred from the Spinulosida to the Valvatida and assigned a position near to the Oreasteridae, from which it appears derived. Acanthaster is not considered to be morphologically isolated and therefore in itself does not imply the past existence of a once more diverse group of which it is a part, as has been suggested. Acanthaster morphology may have evolved in association with the habit of crawling over irregular topographies in higher energy environments. An undescribed Eocene oreasterid shows that a potential Acanthaster ancestral morphology has been in existence at least since that time.