Echinoidea

Echinoidea is a class of marine animals that includes sea urchins and sand dollars. They are characterized by their spiny skin and five-fold symmetry. Echinoidea is part of the phylum Echinodermata, which also includes starfish and sea cucumbers.

Anatomy

Echinoidea have a hard, calcareous shell called a test, which is covered in spines. The test is made up of numerous plates that are fused together. The spines, which are movable, are used for locomotion and defense. Echinoidea also have tube feet, which are part of their water vascular system. These tube feet are used for movement and feeding.

Diet

Most Echinoidea are herbivores, feeding on algae and other plant material. However, some species are omnivores or detritivores, feeding on dead organic material. They use their tube feet and spines to capture and manipulate food.

Reproduction

Echinoidea reproduce sexually, with separate male and female individuals. They have a unique reproductive system, with five gonads that release eggs or sperm into the water. Fertilization is external, and the resulting larvae are planktonic, drifting in the water until they settle and metamorphose into adults.

Classification

Echinoidea is divided into two subclasses: Euechinoidea, which includes sea urchins, and Cidaroidea, which includes pencil urchins. These subclasses are distinguished by differences in the structure of their tests and spines.

Ecology

Echinoidea are found in all oceans and at all depths, from the intertidal zone to the deep sea. They play important roles in their ecosystems, both as grazers that control algal populations and as prey for a variety of predators.

See also

• Echinodermata
• Sea urchin
• Sand dollar

Echinoidea Resources
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