Starfish
A marine echinoderm with a central disk and usually five or more arms. Starfish move on tube feet and often regenerate lost body parts.
Water vascular system: A fluid-filled canal network in echinoderms that powers tube feet and supports movement, feeding, and gas exchange. Its hydraulic pressure lets starfish extend and operate their tube feet.
Echinoderm: A marine invertebrate in a group characterized by a water vascular system and, in adults, usually five-part radial symmetry. Starfish belong to this animal phylum alongside sea urchins and sea cucumbers.
Crown-of-thorns starfish: A large, venomous starfish that feeds on reef-building corals across the Indo-Pacific. Population outbreaks can cause extensive damage to coral reefs.
Common starfish: A widespread northeastern Atlantic starfish, Asterias rubens, with five arms and a variable orange or purple coloration. It is a familiar example of a five-armed starfish and a predator of shellfish.
Brittle star: An echinoderm with a distinct central disk and slender, flexible arms used for movement. Brittle stars are close relatives, but their arms move differently and are sharply separated from the disk.
Tube feet: Small, fluid-operated appendages used by echinoderms for movement, attachment, and handling food. Starfish use rows of tube feet to crawl and pry open prey.
Pentaradial symmetry: A body plan organized around five repeated regions radiating from a central axis. The five-part arrangement is especially visible in many starfish arms and internal organs.
Acanthaster planci: A scientific name historically applied to the crown-of-thorns starfish, now associated with a species complex. Its taxonomy matters when comparing outbreaks and management across the Indo-Pacific.
Sunflower sea star: A large northeastern Pacific starfish, Pycnopodia helianthoides, that can have up to 24 arms. Its many arms and rapid movement contrast with the familiar five-armed form.
Sea urchin: A usually globular echinoderm with a rigid test and movable spines. Sea urchins share the echinoderm body plan but lack the starfish’s prominent arms.