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Can Starfish Have Six Legs?

Over the last couple of months, we have noticed more and more people asking about starfish with six legs due to people seeing them in their aquarium, sometimes without even expecting it!

Now, you may think that it is strange to accidentally end up with a starfish in your aquarium but depending on the situation, the can be accidentally added to your tank in substrate, plants, or live rock.

This is why so many people have been reaching out about having six legged starfish in their aquarium tanks recently.

After seeing so many people reaching out to ask about what the starfish with six legs in their tank is or how it got there, we decided that we want to publish this article to try and help as many of our readers as possible.

Can Starfish Have Six Legs?

Although most starfish commonly kept in the aquarium keeping hobby only have five legs, there are starfish out there that have six legs.

There are also a number of animals that look very similar to starfish that also have six legs too.

Although these similar animals are not technically starfish but a close relative, they are commonly confused with starfish in the fish keeping hobby so we will be referring them to six legged starfish for the purpose of this article.

Here is a breakdown of the four different ways that you may end up with a six legged starfish in your aquarium.

Six Rayed Seastar

The six rayed seastar is the only official member of the starfish family that has six legs.

It is not very common within the aquarium keeping hobby but there are a small number of people in the USA who keep them in their tanks.

If you have purchased substrate, plants, live rock, or decorations from people who keep six rayed seastars in their tank then this may be how you have accidentally added them to your tank.

Six Rayed Seastars are predators and will often eat anything they can catch so they are not usually recommended for community tanks.

The conditions required in a tank with six rayed seastars are not beginner friendly too and many of them accidentally added to marine or reef tanks will die due to the conditions not being optimal for them to live long.

Asterina Sea Star

The Asterina sea star is not a member of the starfish family but they are commonly confused with starfish in the aquarium keeping hobby.

These animals have six legs and can be found in substrate, plants, or live rock that has been collected from the wild.

They are often added to aquariums by mistake as many people do not know that they exist.

Asterina sea stars are not predatory like the six rayed seastar but they do have the ability to reproduce asexually.

This means that if just one of them is added to your aquarium, over time they can grow in number and end up taking over your tank.

They are also known to eat corals and other invertebrates in the aquarium so they are not recommended for reef tanks.

Brittle Star

Brittle starfish are another member of the echinoderm family that is often confused with starfish.

They have a very similar appearance to starfish and can often be found in the same areas as them too.

Brittle starfish can have five or six legs depending on the species but they are not actually related to starfish at all.

Due to living in very similar conditions, they have evolved to have a similar look so many people within the fish keeping hobby confuse them with starfish.

Depending on your tank setup, you can keep them as an inhabitant of your tank but some types of brittle star can grow to huge sizes in optimal conditions.

In addition to that, a small number of six legged brittle stars will eat their tank mates and corals too so many people try to get rid of them quickly.

Mutant Starfish

Although very rare, there are some documented cases of mutant starfish growing a sixth leg.

This can happen with any five legged starfish but it is rare that the sixth leg will originate from the center of the starfish.

The majority of the time, it will actually grow out of one of the five main legs but function as its own independent leg.

Depending on the specific species of mutant starfish you have, some of them can fetch a high price amongst people who like to keep unique and rare animals in their tank.