Sea Urchin

A sea urchin is a spiny, globular echinoderm that lives in all of the world's oceans. They are related to starfish and sand dollars and are known for their hard, spherical shell called a test, which is covered in sharp spines.

Sea urchins have a spherical or flattened body with a hard, rigid shell called a test. This test is covered in long, movable spines that are used for protection, locomotion, and burrowing. Underneath their spines, they have a large number of flexible tube feet with suction cups that help them move and cling to surfaces. Their mouth, located on the underside of their body, is equipped with five hard plates that form a jaw-like structure called Aristotle's lantern, which they use to scrape algae and other food.

Sea urchins are found in a variety of marine environments, from shallow tidal pools to the deepest parts of the ocean. They are typically herbivores and play a crucial role in controlling algae growth on coral reefs. Their diet consists mainly of algae, but they will also eat sessile animals, such as sponges and barnacles.

Sea urchins are a keystone species in many marine ecosystems. Without them, fast-growing algae can outcompete and smother coral reefs, a phenomenon known as "algal blooms." By grazing on algae, sea urchins help maintain the health and diversity of coral reefs. However, a decline in sea urchin populations due to disease or other factors can have a devastating impact on the health of a reef.