Figure 32.5 Echinoderm Diversity (A) The flexible arms of this variable bushy feather star (a crinoid) are clearly visible. (B) Sea urchins are important grazers on algae in the intertidal zones of the world’s oceans. (C) This sea cucumber has expelled a portion of its viscera as a sticky defense against a potential predator. (D) Sea stars are important predators on bivalve mollusks such as mussels and clams. Suction tips on its tube feet allow a sea star to grasp both shells of a bivalve and pull them open. (E) The arms of a brittle star are composed of hard but jointed plates.