Instead, it appears that these ancient groups have been outcompeted in shallow waters by more recent taxa. The closest living relative appears to be the bizarre, abyssal Xyloplax-a small genus of tiny, armless xylophages (wood eating) so unusual that it was originally described as an entirely new taxonomic class of echinoderm.įrom this modern ecological data, it is tempting to infer that the last common ancestor of the sea stars would have evolved in a similar abyssal habitat, but Cretaceous fossils indicate the shallow water species (much like Euretaster and Pteraster) were formerly plentiful. Credit: Brian MayesĪs the presumed earliest diverging lineage of living sea stars, the Velatida grant us valuable insight into the origins of sea stars as a whole. These three families together constitute the Order Velatida, whose only shallow water tropical species are indeed Euretaster. The remaining genera and species are ecologically limited to extreme depths, as are the members of two small and closely-related families. On the other hand, recent molecular studies have shown Euretaster belonging to the basalmost clade, which indicates it belongs to a particularly ancient and undiversified lineage.Įuretaster is classified within the Family Pterasteridae, whose other common representatives are the “Slime” or “Cushion Stars” ( Pteraster) commonly found in tidepools throughout the temperate waters of the Northern hemisphere. Traditional morphological studies have placed it as a highly derived group amongst the more “advanced” clades. The position of Euretaster within the sea star tree of life has been contentious. So let’s draw back the curtain and summarize what little is known of these enigmatic creatures. Almost nothing has been written on this group in terms of aquarium husbandry, and the scientific literature is similarly empty on basic elements of its biology. One of the most interesting species-morphologically, behaviorally and evolutionarily-is also one of the most seldomly encountered: the “Striking Sea Stars” of the genus Euretaster.
Despite the diversity of sea stars that abound in tropical waters, relatively few species find their way into aquariums with any regularity.