Tunicates – an unexpected relative in the ocean
At first glance, tunicates hardly look remarkable. Often mistaken for sponges, blobs, or bits of rock glued to piers and reefs, these soft bodied marine animals are easy to overlook. Yet tunicates (also known as sea squirts) are among the most fascinating organisms in the ocean – not only for their unusual lifestyles and striking diversity, but because they are the closest living invertebrate relatives of humans.
Their name comes from the tunic – a tough, flexible outer layer that protects the animal. This tunic is unique in the animal kingdom because it contains cellulose, a material more commonly associated with plants. Tunicates are found in oceans all over the world, from shallow coastal waters to the deep sea. There are over 3000 known species globally and most species are sessile as adults, meaning they live permanently attached to a surface such as rocks, shells, or manmade structures (including Virtue discs!).
Tunicates come in two main forms: solitary and colonial. Solitary species, such as Ciona intestinalis, live as individual animals. Colonial tunicates form living networks of genetically identical individuals that are connected by shared tissues. These colonies can take beautiful and sometimes bizarre forms – stars, branching structures, or colorful blobs.
Despite their simple appearance, tunicates are highly efficient filter feeders and play an important role in marine ecosystems by cycling nutrients and helping to maintain water quality. In several parts of the world, tunicates (e.g. Ciona intestinalis) are also eaten as seafood. Some tunicates produce bioactive compounds that are being studied for pharmaceutical use, including anticancer and antiviral properties. This makes them part of the growing field of marine biotechnology.
Tunicates may be humble in appearance but play an important role in the ocean.