starfish

 12 interesting facts about starfish

Starfish, also known as sea stars, are sea creatures known for their star-shaped appearance and vivid colors. While many people imagine a starfish to have five arms, some species claim up to 40 arms. These unique echinoderms move using their tube feet, regenerate lost limbs, and have an interesting feeding apparatus attached to their stomach.

Sea stars are not fish

Despite living in water, sea stars are not fish. Unlike fish, they lack gills, scales and fins. They navigate using small tube feet instead of a tail.

Sea stars are echinoderms

Part of the Echinodermata phylum, sea stars are related to sea urchins, sand dollars, and sea cucumbers. These organisms typically exhibit radial symmetry, meaning that their body parts radiate from a central axis.

Countless species of sea stars

About 2,000 sea star species inhabit a variety of marine environments from tropical to polar regions.

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Not all sea stars have five arms

While many sea stars have five arms, others have more, such as the sun star, which can have up to 40 arms.

Sea stars can regenerate organs

Sea stars can regenerate lost arms, a useful trait when avoiding predators. Some species can even regrow an entire sea star from part of an arm and a central disc.

Protective cover on sea stars

Sea stars have a hard exterior with spiny plates made of calcium carbonate for protection from predators such as birds, fish, and sea otters.

Sea stars are anemic

Instead of blood, sea stars have a seawater-based circulatory system. Sea water flows through the madreporite into their water vascular system, a light-colored spot often visible on the top of the starfish.

Sea stars move with tube feet

Sea stars rely on tube feet on their undersides to move around using seawater brought up through the madreporite. This method allows them to move fast and catch prey such as clams and mussels.

Eating from the stomach in and out

Sea stars consume prey such as clams, mussels, small fish, mollusks, and barnacles. They open the shell of the prey and then expand their shell through the mouth, digesting the food before expelling their stomach.

Starfish have eyes

Amazingly, starfish have eyespots at the end of each arm, which allow them to detect light and darkness. The five-armed sea star has five eyes, while the 40-armed sun star has 40 eyes.

True starfish belong to Asteroidea

Starfish comes under the animal class Asteroidea. These "true stars" are distinct from brittle stars and basket stars, which have a more pronounced separation between their arms and the central disk.

Two methods of reproduction

Sea stars reproduce sexually by releasing eggs and sperm into the water, and asexually through regeneration when they lose an arm.