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Echinoderms are deuterostomal animals with radial symmetry and a calcareous endoskeleton. They include starfish, sea urchins, sea cucumbers and others. Learn about their taxonomy, evolution, diversity and ecological importance.
Madreporite is a sieve-like structure on the upper surface of sea stars that allows water to enter the water vascular system. The system consists of canals, tube feet, and coelomic cavities that enable locomotion, feeding, and respiration in echinoderms.
Another invagination of the surface will fuse with the tip of the archenteron as the mouth while the interior section will become the gut. At the same time, a band of cilia develops on the exterior. This enlarges and extends around the surface and eventually onto two developing arm-like outgrowths. At this stage the larva is known as a bipinnaria.
Ossicles are calcareous elements embedded in the body wall of echinoderms, such as sea urchins, starfish, brittle stars, sea cucumbers, and crinoids. They form part of the endoskeleton and provide rigidity and protection, and have various forms and arrangements depending on the echinoderm group.
A hydrostatic skeleton or hydroskeleton is a type of skeleton supported by fluid pressure, common among soft-bodied invertebrates. Learn about its structure, advantages, disadvantages, and examples of organisms with hydrostatic skeletons.
Endoskeleton is a structural frame on the inside of an animal, usually composed of mineralized tissue. Learn about the endoskeletons of vertebrates, invertebrates, and cephalopods, and how they differ in shape, support, and locomotion.
Tunicate is a subphylum of chordates that includes about 3,000 species of sea squirts, sea tulips, and other filter feeders. They have a water-filled sac-like body, two siphons, and a protective tunic, and are closely related to vertebrates.
Eocrinoidea are extinct stalked, arm-bearing echinoderms that lived from the Cambrian to the Silurian. They may be ancestral to modern crinoids and other classes of echinoderms.