Echinoderms show the unity of life in the structures which they share (apparent five-way symmetry, rows of tube feet), but they show diversity in how those are modified (tube feet used for locomotion in some, filter feeding in others; elongated body plan in sea cucumbers). These variations all suit how the particular echinoderms live in their niches, with starfish crawling over rocks with their sure tube feet and sea lilies using their long, feathery arms for filter feeding.
Work Step by Step
To get this answer, review the definitions of things like biological unity/see Concept 22.2, and review the information on Concept 33.5. Use your imagination to fit the information from this chapter with those definitions.