A photo of some wide-mouthed sea creatures that seem to be screaming into the ocean void has been making the rounds on social media.

These bizarre-looking animals even have an adorable name to match their comical faces: sea squirts.

However, while these sea squirts may appear to have two eyes and a mouth in that photo, they don't technically have eyes or mouths at all.

Sea squirts are invertebrates known officially as tunicates, and there are more than 3,000 known species. They come in a variety of colors and shapes, but they're typically cylindrical.

They live on rocks, coral and other hard surfaces on the ocean floor, and they feed on plankton and other organic matter, which they strain fro water pumped through their bodies.

As one blogger puts it, a sea squirt is "basically a big stomach inside a sack."

In addition to posing for viral Internet photos, sea squirts are also well known for "eating their own brains." Although, this is much less disgusting and dramatic than it may sound.

Here's how the brain eating works: Sea squirts are hermaphrodites, meaning they have both male and female reproductive organs, and they spawn by releasing eggs and sperm into the ocean.

When the fertilized eggs develop into larvae, they look a lot like tadpoles and they're able to swim freely about. However, they're unable to feed at this stage.

In order to eat, they must find a place on the ocean floor, where they'll spend the rest of their lives. Once they've settled, the sea squirts absorb all the parts of their body they no longer need — their tails, their gills and even their brains.

Although these strange creatures may not seem like much, they're actually highly evolved for invertebrates, and they contain many potentially useful compounds that show promise in treating diseases like melanoma and breast cancer.

Below, take a look at just a few of the thousands of types of sea squirts that inhabit the ocean.

different types of sea squirts

Photo: Wikimedia Commons

transparent sea squirt

Photo: Jannah Brown/flickr

yellow sea squirts

Photo: Rob/flickr

bright sea squirts

Photo: Samuel Chow/flickr

green sea squirts

Photo: Wikimedia Commons

sea squirts

Photo: Silke Baron/flickr

white sea squirst

Photo: Gordon Milligan/flickr

transparent tunicates

Photo: Wikimedia Commons

fish on sea squirt

Photo: Silke Baron/flickr

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