1. marine animals belonging to the class Echinoidea, including sea urchins and sand dollars, characterized by a round or flattened body covered with spines
Usage: zoological term; plural form

Examples

• The tide pools were filled with colorful echinoids clinging to the rocks.
• Marine biologists study echinoids to understand ocean ecosystem health.
• Fossil echinoids provide evidence of ancient marine environments.
• The aquarium’s touch tank featured several species of echinoids.
• Echinoids play an important role in controlling algae growth on coral reefs.
• The beach was littered with the empty shells of dead echinoids.