starfishs

Starfish, commonly called sea stars, are marine invertebrates in the phylum Echinodermata and the class Asteroidea. They are not fish. Most species have pentaradial symmetry with five or more arms radiating from a central disk and use a water vascular system to move and feed. The term starfish is traditional, but many scientists prefer sea star as a more accurate name.

Anatomy and physiology: Starfish have an endoskeleton made of calcareous plates, a network of canals forming the water vascular system, and tube feet with suction cups. The mouth is on the oral side; the opposite surface is the aboral side. In some species, eyespots are located at the tips of the arms. Many starfishes can regenerate lost arms, and some can even regenerate an entire animal from a single arm plus part of the disk.

Habitat and distribution: Starfish are found in oceans worldwide, from shallow tide pools to deep seafloors. They inhabit rocky shores, coral reefs, seagrass beds, and soft sediments. Size ranges from a few centimeters to over a meter in width.

Diet and feeding: Most starfishes are predators or scavengers. They commonly feed on mollusks such as clams and snails, crustaceans, or coral polyps. They can extrude their stomachs through their mouth to digest prey externally before absorption of nutrients.

Reproduction and life cycle: Starfish reproduce sexually by releasing eggs and sperm into the water column, with free-swimming larval stages such as bipinnaria and brachiolaria. Some species also reproduce asexually by fragmentation or fission.

Evolution and conservation: About 2,000 living species are described. Fossils date back to the Cambrian period. Starfish face threats from habitat loss, climate change, and disease, including sea star wasting syndrome in some regions. They are subjects of ecological and developmental research, notably for their regenerative abilities.