How sea stars regrow limbs and why they aren’t really ‘starfish’

Difficulty: Challenger (Level 2)

The ocean is home to many unique creatures, and the sea star is one of them. These colourful, spiny animals belong to a group called echinoderms. This means their bodies are built around a central point. For sea stars, their arms branch out from the centre of their body.

A more common name for sea stars is starfish. However, scientists prefer to call them sea stars because they do not have the body parts that other fish do, such as gills and scales.

In fact, they do not even have a brain because they do not have a nervous system to send signals to the rest of the body. And instead of having blood, they take in seawater and pump it throughout their bodies.

The seawater also helps them to move. Sea stars have lots of tiny tube feet on their underside. When they want to move a foot, seawater gets pumped into it, causing it to extend and reach out. Then, the muscles squeeze the water back out, making the foot contract and pull the sea star forward.

Sea stars are also famous for their ability to regrow a lost limb. This is because their arms have some of their main body parts. But replacing a lost arm can take months or even a year.

Scientists are studying sea stars to understand how their cells can regenerate lost body parts. This might help them to come up with cheaper and quicker treatments for diseases using special cells called stem cells.

Questions

• What are some other examples of sea animals that are echinoderms?

• Why are scientists studying sea star regeneration?