Euretaster insignis
Euretaster insignis, commonly known as the striking sea star, is a species of starfish in the family Pterasteridae found in the central west Pacific Ocean. It is one of only three species in the order Velatida to be found in shallow water in the tropics. The young are brooded in a cavity underneath a "supradorsal" membrane.
Taxonomy and evolution
This starfish was first described in 1882 by marine biologist Percy Sladen as Retaster insignis, Retaster being a small segregate genus of Pteraster. In 1940, the genus had to change its name after Walter Kenrick Fisher noted that the type species of Retaster he had himself designated, Pteraster capensis was in fact a sound species of Pteraster, which automatically made the former genus a synonym of the latter. The genus known as Retaster required a new name, and the one Fisher coined was Euretaster, with R. insignis as its type species.The order Velatida are presumed to be the earliest lineage of living sea stars to diverge from the ancestral line, their closest living relatives being the abyssal sea daisies in the order Peripodida. The three members of the genus Euretaster are the only tropical, shallow-water species in the order Velatida, the remaining members living at abyssal depths. It might be presumed that the order has its origin in deep water, however there are numerous shallow-water fossils of velatidans dating from the Cretaceous period and it seems that these ancient forms have largely been driven out of shallow water habitats by competition from recent, more-advanced taxa.