Task: Text Categorization
Input (English): One member of this phylum was the textbook ""keystone organism,"" whose biological impact is large proportionate to its biomass in an ecosystem. Members of this phylum have exterior ""tube feet,"" which are extensions of their water vascular systems. This phylum contains radially symmetric organisms like sea cucumbers, sand dollars, and crinoids. For 10 points, name this animal phylum whose members include starfish and sea urchins, the name of which means ""spiny skinned. ""
Output (English): Science