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.

Clavelina robusta often occurs in dense clusters. Nick Hobgood [CC by 3.0]/Wikimedia Commons

It looks like the thinnest spider is crawling on this sea squirt. Jannah Brown [CC by 2.0]/Flickr

Fluorescent-colored sea squirts in the Lembeh Strait. Samuel Chow [CC by 2.0]/Flickr

A colony of green ascidians from East Timor. Nick Hobgood [CC by 3.0]/Wikimedia Commons

These blue sea squirts look like veiny gourds. prilfish [CC by 2.0]/Flickr

Sometimes sea squirt look like pasta. gordon.milligan [CC by 2.0]/Flickr

These blue-ringed transparent sea squirts also look like springy coils. Nick Hobgood [CC by 3.0]/Wikimedia Commons