Echinid is a noun that refers to any member of the taxonomic class Echinoidea, which comprises sea urchins and sand dollars. These marine invertebrates belong to the phylum Echinodermata, sharing characteristics such as a radial symmetry and a hard, spiny or plate-like exoskeleton called a test. Echinids are typically found in oceans worldwide, inhabiting diverse environments such as shallow coastal waters, coral reefs, sea grass beds, and even the deep sea.
The bodies of echinids are nearly spherical or disc-shaped, and they possess a unique water vascular system that aids in locomotion, respiration, and feeding. This hydraulic system, powered by water-filled canals, controls movement through a series of tube feet. Echinids also have an intricate mouth apparatus known as Aristotle's lantern, which is composed of five interlocking teeth used for grazing on algae, detritus, or small organisms.
The exoskeleton of echinids is covered in spines, which may serve protective or locomotory purposes. The spines can vary significantly in size, shape, and color, and they can be dynamic, helping the organism move or adjust its position. Additionally, some echinids possess tube feet modified as pedicellariae, which act as pincers or pinchers for removing debris or deterring predators.
Echinids play vital roles in marine ecosystems, contributing to nutrient cycling, algae control, and providing habitat for other organisms. They are also of ecological and economic importance, being both a food source for certain predators and highly valued as ornamental objects in various cultures. Additionally, echinids have gained attention in scientific research due to their regenerative abilities and unique biological features, making them subjects of interest
