They actually squirt when you squeeze them, as their name implies. But, they’re much more complicated creatures than you might think. And they are more closely related to humans than many animals that live in the ocean. Sea squirts are these strange, glassy little sacs that somewhere in their tiny soft bodies have a kind of a simple dorsal nerve or chord. That’s what defines the phylum Chordata, which also includes humans. In humans, that dorsal nerve evolved to have a spinal column to protect it that is composed of vertebrae. That makes us vertebrates. Sea squirts don’t have vertebrae or any bones, which makes them invertebrates – the group to which many intertidal animals belong. They are more specifically a type of tunicate, which means they have a soft “tunic” around their bag-like body.

I was recently reintroduced to these slimy relatives on some washed up fishing gear appeared after the recent tropical storm. They form a jelly-like coating on surfaces that at first look slimy and not very interesting. But, as with many seemingly simple animals, when you look more closely, they are quite complicated and beautiful. The particular species I found was Ciona intestinalis, which translates to “pillar of intestines” in Latin. Each vase-shaped body (it’s also known as a vase tunicate) does actually look like it is filled with a squiggling little thread of intestines. The bottom of the vase is attached to something hard – a rock, a dock, a rope, for example. The top of a sea squirt is actually more like a double vase – one takes water in and one squirts it back out as they filter out tiny plankton form the water. That’s why, when you press on them, they squirt out at you. This is a lot like clams that have intake and outtake siphons. It’s a bit less like humans, unless you regularly breathe up one nostril and out the other.

While they are individually lovely creatures, en mass they can be problematic. That’s because they don’t very often live alone. Instead, they form colonies. They do this either by budding off little parts of their bodies into new baby squirts or by releasing larvae into the water that then settles into new spots. These colonies can get quite large and cover big portions of surfaces, weighing them down and clogging up openings. This is not very convenient for fishermen or others keeping gear in the water. As with many species that cause problems in Maine waters, sea squirts are not native to Maine. They likely arrived in the ballast water of ships coming from places far away sometime in the early 1990s. Because they release larvae into the water, they can drift and settle just about anywhere there are nutrients. They also don’t have natural predators, as is also often the case with invasive species, so they can reproduce like crazy and not be eaten

Piles of intestines aren’t the only type of problematic tunicate in Maine. Sea vomit is another lovely addition to the mix. Scientifically known as Didemnum spp., this one is native to Japan and some parts of Europe. Its form is imaginable from its name, although the more genteel name is pancake batter, which aptly describes its drippy thick consistency. That makes it hard to scrape off of pilings, lobster traps, or fishing nets. And they often just reappear soon after in just the same place. There was an area found on Georges Bank in 2003 that six square miles large and was covered in this “batter.” Apparently, they can increase their size six-fold in about two weeks and fourteen fold in a month!

So, what can be done about these gelatinous relatives of ours? No one, to my knowledge, has explored eating them, which is often one approach. Green crabs, for example, have sparked many creative ideas from local chefs. The best thing people have found is to dry them out. Because they are jelly-like and because they need water to filter out food, they don’t live long out of water. Fortunately, people have become more aware of introducing species and there are better practices in place to prevent future introductions. In the meantime, perhaps we can at least enjoy looking at them up close and wondering at our own evolution and advancement from these lowly creatures.