Tunicates

Tunicates are also known as ascidians or sea squirts. They have a simple structure where they create a current through their siphons to bring water into their body cavity. There, they collect the little pieces of plankton or detritus – decaying organic matter from the water in a mucus net and push out the left over water.

Like other filter feeders, tunicates are important creatures for the entire ecosystem.

They help keep things in balance.

The name tunicate comes from their outer protective covering or tunic. The tunics and other parts of the tunicate body contain cellulose, something they have in common with plants. Some species use their tunic as a defense mechanism by storing acidic compounds – not very tasty for predatory fish or crabs.

This species of painted tunicate pictured here, Clavelina picta, is common in the shallow waters of the Caribbean and in Bermuda. It attaches itself to other organisms like sponges and soft corals and lives in colonies of hundreds of individuals. They are mainly asexual so they bud (multiply) into clone tunicates to add to the colonies.

The eye catching bright pink outline made painted tunicates one of my favorite animals to see underwater during my study abroad experience at the Bermuda Institute for Ocean Sciences. Their simple structure also fascinated me.

For something so simple, they are actually one of the most evolved (speaking only in terms of evolutionary time) invertebrates. They are urochordates, meaning that they have primitive spinal chords and that next in line after the true chordates they are our closest relatives. So even though tunicates may look like a bag of jelly, they have been pretty successful.

Why should we care about these little jelly bags? Well besides being an important filter feeder for the ecosystem they may also be the source of chemical compounds that could have medicinal uses, even against cancer.

Read more here about how tunicates are being used in regenerative medicine.

Tunicates can also be a stowaway in the ballast water of ships. This can potential bring invasive species into new environments where they can disrupt or even destroy the local environment. For example, there are Didemnum species that can cover the entire sea floor, literally suffocating the local marine life. This can also cause economic impacts, an example being if there are oyster beds on the bottom being covered in quickly multiplying tunicates.

Learn more about Didemnum here.

So while they are either killing ecosystems or curing cancer, tunicates are an animal that scientists will continue to learn more about for years to come. Pretty powerful for a little bag of jelly!

Photos by Sara MacSorley off the coast of Bermuda