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Sea Star; Biscuit

Sea Star; Biscuit

Tosia australis

The Biscuit Sea Star is a species of the phyla Echinodermata and part of the class Asteroidea. They get their common name from the resemblance they bear to a homemade biscuit. Like all echinoderms, Biscuit Stars have pentagonal symmetry, a body plan based on 5 symmetrical radiations. On the oral side (underneath) is the mouth and a complex network of tube feet which are powered by a water vascular system. Tube feet are used for both locomotion and transporting food to the oral disc. Biscuit Stars are widely distributed throughout Australia’s southern half with their range extending from Sydney, NSW, around Tasmania and across to Western Australia in coastal waters to 0-40m depth. The colouring and patterns of this species are extremely variable amongst individuals, even those in a single location and includes brown, orange, purple, pink and yellow. Very rarely are specimens a single colour. Characteristic of this species are the 6-8 marginal plates along the edge of each of the arms. They feed upon ascidians, bryozoans, sponges and algae.

Occurrence at the Busselton Jetty:   

Biscuit Sea Stars are commonly observed on the piles around the Underwater Observatory, however close observation is required to distinguish these animals from other sessile invertebrate growth on the piles. They are easily identified by their short stubby arms and pentagonal shape.

Image by: O. Rynvis