; subphylum Asterozoa, class Stelleroidea)
A subclass which includes all extant starfish, characterized by the possession of poorly demarcated, broad arms containing a large coelomic cavity. The open ambulacral grooves bear rows of large tube feet which are used especially in feeding and locomotion. Respiration takes place through external gills (papulae) which are restricted to the aboral surface. Asteroids occur from the Ordovician to the present.
Subjects: Zoology and Animal Sciences.