Today is World Aquatic Animal day, so I’m taking this opportunity to present 10 facts about an animal I’ve not had the chance to cover yet, the starfish.
First of all, they are not Fish. They are part of a group of animals known as echinoderms, which also includes sea cucumbers, sea urchins and Sand Dollars. Because they are not fish, scientists prefer to call them "sea stars."
They don’t have Brains or Blood. They use sea water to pump nutrients through their bodies.
Their mouths are on their underside. They can however eat things that won’t fit in their mouths by essentially turning themselves inside out, so that their stomachs are on the outside and can digest the food before ingesting it.
There are about 2,000 species of sea stars. While we tend to visualise them with five arms, some species have as many as 40.
Their rudimentary Eyes are situated on the ends of their arms, so depending on the species, they can have as many as 40 eyes. Each arm also has hundreds of little feet to help them move on the sea floor.
If a starfish loses one of its arms it’s not the end of the world, because they can grow another one. However, it’s not something they’d do lightly as an arm will take about a year to grow back. In addition, the severed arm, provided it’s not eaten by something, can grow into a whole new starfish.
Starfish can weigh up to 11lbs and live for up to 35 years.
Their skin is made from calcium carbonate, which is tough like armour and difficult for predators to break down. Some species add spines as an extra defence as well.
Starfish are easy to study in a lab because they are easy to handle in seawater at room temperature, and they develop quickly. They are of particular interest to scientists because of their ability to regenerate. However, studies involving tracking them are a bit more tricky. Starfish also have an unusual ability to expel foreign objects from their bodies, so they will spit out any tracking devices people might try to attach.
The most famous fictional starfish is probably Patrick Star, the best friend of SpongeBob SquarePants.