Assertion: echinoderm's endoskeleton | /r/RelatedTo | external tube foot
Facets:
Source sentences:
text: Star-shaped or pentagonal; 5 or more arms merged gradually to central disk; endoskeleton flexible; ampullae (internal bulbous swelling associated with the external tube foot) single-lobed, bilobed in one species; short spines and pedicellariae.