All sea stars share the classic star shape, and most of them have five arms. Sea stars have their mouth on the underside of the body, so when feeding the animal extrudes its stomach over the prey to be digested. Most sea stars are carnivorous, eating worms, corals, molluscs and crustaceans, others feed on algae and seagrass, but in turn they are preyed upon by fish, molluscs, crustaceans and other seastars! Some sea stars have small shrimp that live on them.
Crown-of-Thorns Starfish (COT) – Acanthaner planci – are larger starfish reaching 40cm in diameter. They have no eyes, but hey do have eye spots on the end of each arm, these can only detect changes in light and dark. They move around using thousands of tiny tube feet that move using an internal water canal like system. They have between 18-20 arms, which are covered in poisonous spines. They can regenerate arms if they lose them OR can regenerate a whole new body from one arm. In normal numbers crown-of-thorns help to keep the reef healthy by eating fast growing coral, allowing slower growing coral to thrive. However the population can explode devastating whole reefs. Scientists do not yet know whether this is a natural occurrence or due to human impact. Attempts have been made in some areas to remove the COT from reefs and disposing of them offshore, however this is a controversial practice. The Triton trumpet shell (genus Charonia) is a predator of COT. Sadly their numbers are in decline due to the curio trade.
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