echinoid

Echinoids, belonging to the class Echinoidea within the phylum Echinodermata, are marine invertebrates characterized by a globular body enclosed in a thin, brittle test (internal skeleton) covered with movable spines. These spiny creatures are found in all marine waters worldwide, from shallow shores to the deepest ocean trenches.1234

Sea urchins, a common type of echinoid, typically have a radial arrangement of organs, with five bands of pores accommodating tube feet that aid in movement. They possess a complex dental apparatus called Aristotle's lantern, used for scraping algae and other food from rocks. Some echinoids can excavate hiding places in rock or coral, and their spines can be quite long and sometimes venomous. Echinoids play a role in their ecosystems by controlling seaweed growth in coral reefs, though large populations can also damage sea-grass beds and accelerate shoreline erosion.56