Sea star

Often brightly coloured, these animals belong to the phylum Echinodermata, meaning spiny skin and includes sea urchins, sea cucumbers, brittle stars and feather stars.

Sea stars have five or more arms radiating out from a central disc, however some can grow up to 50. Their tube feet, which in most species end in suckers, are set in grooves along the underside of the arms. These assist the sea stars in mobility and feeding. At the end of each arm is an light sensitive eyespot that allows the animal to detect movement and shadows.

Under the centre of the body is the mouth. By pushing their stomach out of their mouth, sea stars are able to pry open the shells of bivalves (such as clams and mussels) and other shell fish or snails, consuming their prey with their stomachs outside their body.

Found in oceans throughout the world, sea stars occupy every habitat, such as tidal pools, kelp beds and coral reefs. The deepest observed sea star was found at a depth of 7,176m! Sea stars are a common marine animal and are not currently under threat. Next time you are at the beach you can look for the skeleton of these animals, they are often washed up on the shore but lack the beautiful colours and patterns they display whilst alive.

A biscuit sea star

Did you know?

Sea stars can regrow lost arms, or even a whole new body! Sea stars can perform asexual reproduction in two different ways – fission and autonomy of arms. Fission involves the central disk breaking into two pieces, and regrowing into two new animals. Autonomous asexual reproduction involves the shedding of an arm with a portion of the central disk still attached. Each arm contains parts of the digestive tract and reproductive organs, allowing it to function on its own. This process of regeneration is slow, and may take a year for complete regeneration.

Sea star arm displaying tube feet

Bibliography

https://australian.museum/learn/animals/sea-stars/

https://kids.nationalgeographic.com/animals/invertebrates/facts/sea-star

https://www.visitsealife.com/sunshine-coast/information/news/facts-about-sea-stars/