Answer:
sea urchin
Step-by-step explanation:
An echinoderm is an invertebrate animal (without backbones) that belongs to the Echinodermata group. Members of the echinoderm group are characterized by their possession of a star-shaped and spiny-skinned morphology. They are found strictly in marine habitats. They include sea urchins, sea cucumbers etc.
According to this question involving an echinoderm that is covered with movable spines and that eats seaweed, this describes a SEA URCHIN. This is due to the possession of the MOVABLE SPINES by sea urchins. Sea urchins, like other echinoderms, are predatory and feed on seaweed (algae) as well.