Up there with some of the most beautiful and extraordinary creatures in the world’s oceans, there’s a lot that’s odd about the starfish – right down to its name.
With 2,000 different species of them, in all sorts of amazing colours, shapes and sizes, starfish are truly in a league of their own. Let’s take a look at these unique animals in more detail below. Goggles and scuba gear at the ready…
How to identify a starfish
Starfish are easy to identify; there’s not many other animals in the sea that resemble a star, for one. But as a species, they can change a surprising amount – and it’s this info that lets us work out which starfish are which.
All starfish have a central disc with five arms attached, although some species can have six, 12 or even 50 of them! The length of these arms can differ too; the mottled sea star has very long, gangly limbs, while the sunflower star has much smaller ones in comparison.
Starfish belong to the echinoderm family, a term that means “spiny skinned”. However, all starfish have this same texture. Some have smooth skin, while others like the spiny red sea star, as you can guess, have an incredibly spiny surface.
Unsurprisingly, they come in all sorts of different sizes too. The world’s smallest sea star comes in at a very tiny 1.83cm, while at the other end of the scale is the Evasterias echinosoma at 96 centimetres. That centre disc varies in size too. Some can be very small with long, narrow arms, while others can have a large disc with much smaller arms.
Lastly, starfish stand out thanks to the incredible colours they come in. From purple and blue to red and yellow, some species even have patterns too, including bands around their arms, or outlines that follow the entirety of their starry shapes.
The life-cycle of a starfish
A starfish’s life-cycle begins with a process called spawning. This is when male and female starfish release eggs and sperm from their bodies. Some of these sperm and eggs come into contact with each other, and the fertilisation process begins.
In just a few minutes, the zygote which has formed turns into an embryo, before becoming larva. These larvae become travellers, exploring the ocean for days or weeks, where they look for small plankton to eat. Some species do not have this state and instead skip straight to being a juvenile – this phase is called the mesogen.
Starfish with a larval stage become juveniles through metamorphosis, while those with a mesogen phase go through morphogenesis. After a while, the juvenile starfish reach the weight of an adult starfish and are now ready to reproduce themselves.
Where do starfish live?
Starfish can be found all over the world’s waters, including the Atlantic, Arctic, Indian and Pacific oceans, with some also calling the Mediterranean Sea their home too. They have plenty of different living arrangements too. You can find them near docks and at the bottom of bays, chilling in tide pools and lagoons, in kelp forests and on coastlines.
One place you won’t find them though is in freshwater environments. A starfish’s body has a membrane that lets water flow in and out of the cell body. In salty water, this poses no problem to them. But when they find themselves in freshwater, the water invades cells, causing them to swell so much that they can break, killing the cells as a result.
How do starfish eat?
We hope you didn’t eat before you got to this part, because things are about to get a little…interesting.
Starfish stomachs are kind of similar to ours, but that’s where the similarities end. Rather than eating food through their mouth so it can go to the stomach, starfish kind of spit their stomachs through their mouths!
The stomach then essentially wraps around the food and digests it outside of its body. After giving it a good digesting, it pulls in the stomach and swallows everything into its body. Delicious, right?
They have quite the appetite too, feeding on everything from clams, oysters, snails, sponges, sea urchins and a menu of other invertebrates whenever they get hungry! Since some of these prey have hard shells, starfish get to their soft centres by prying them open using their suction-cupped feet.
Are starfish poisonous?
Most starfish are not poisonous, and since they can’t bite or sting us, they pose no threat to humans.
However, there’s a species called the crown-of-thorns starfish which is venomous, and if their spines pierce the skin they can be venomous. Poisonous and venomous can be used to mean the same thing, but there’s a difference. They both cause temporary illness – or worse – but it’s the way poisonous and venomous creatures administer their toxins which makes them distinct.
Poisonous creatures are organisms which unload toxins when they’re eaten, whereas venomous creatures do so by bite or a sting – which is what the crown-of-thorns starfish does.
Where to see starfish at Bristol Aquarium
Our starfish can be found at the Ocean Floor exhibit, alongside a range of other animals including sharks and fish. Come say hi to them!
Fun starfish facts
Want some more fascinating facts about starfish? These intriguing guys get a whole lot more curious after reading the below:
- What is the difference between the starfish and sea star? Well, they’re the same thing, but because a starfish isn’t technically a fish (since they have no spine), marine scientists have opted to use the name sea star instead!
- They don’t actually have a brain, or any blood for that matter. They pump nutrients from seawater to pump nutrients through their nervous system instead
- They’re a lot heavier than you might think – even a small starfish can weigh nearly 5kg
- The average lifespan of a starfish is a whole 35 years, although it’s the larger species that tend to celebrate these birthdays compared to smaller ones
- You’ve probably heard that starfish can regenerate. Well, it’s true! Certain tropical species can form a completely new starfish from just a part of a severed limb, although this does take up to a year to happen. It happened to one of our own starfish a few years ago too – head here to read about how it all happened.
- Their eyes are on the ends of their arms! Starfishes’ eyesight isn’t quite on our level, but they can detect different shades of light so they get around their surroundings.
- There is a starfish which isn’t actually star-shaped. The cushion starfish actually has a round blob-like shape, but is still technically classed as a starfish
What do they eat?
Worms and molluscs
Where are we?
North Atlantic, UK coasts