Range: Marine waters worldwide Habitat: Open ocean and attached to hard marine surfaces Size: Up to 6.5 feet (2m) long as a colony; Up to 7.5 inches (2cm) long as individuals Diet: Plankton and other small particulate matter Threats: Fish and invertebrates Life span: About one year as adults

Transcript:

Today on Animal Fact Files we’re discussing tunicates. These animals might look like they would be closely related to a sponge, but they’re actually more closely related to Chester and even us than they are sponges. Tunicates are classified in the Chordata phylum - which is the same phylum in which humans and cats are classified - sponges, on the other hand, are classified in the phylum Porifera. So, how does something that looks like this have closer ties to something like this than it does to something like this? Anatomy has a lot to do with it.

Chordates are animals that possess a notochord at some point in their lives (among other traits, but we’ll just stick with this one for now). The notochord is a flexible, rod-like structure that, in vertebrates, eventually forms the spine. Tunicates, however, are not vertebrates. In tunicates, the notochord is present during their larval life stage but eventually lost as the animals metamorphose into adults. At no point do tunicates ever possess vertebrae, so they aren’t considered vertebrates even though they’re closely related to vertebrate animals like you and me! Tunicates, however, have green colored blood and they can pump this in reverse throughout their bodies which is something we definitely can’t do!

Tunicates are also known as sea squirts and there are over 2,000 known species. They’re divided into three groups: the ones who are sessile, meaning they attach to a surface such as a rock, the shell of a sea creature, or even the hull of a ship and remain there throughout their lifetimes; and the other two groups which are pelagic, meaning they live in the open ocean, with one looking similar to the sessile tunicates and the other looking more like the tadpole-like tunicate larvae.

Tunicates live in marine seas throughout the world from polar regions to the tropics, from shallow waters to the depths. They get their common name from the leathery “tunic” protecting their barrel shaped bodies. This tunic somewhat functions like an external skeleton by supporting and protecting the tunicate’s body, but what’s fascinating about it is that it’s partially composed of cellulose which is typically not found in animals but is quite abundant in plants!

Tunicates are animals, though, make no mistake. They eat food by filtering it from the water column. Many tunicates have two siphons on their bodies: one which takes in water and one which releases water as well as wastes. The water is circulated through the tunicate’s body via small, hairlike structures called cilia. Most tunicates eat small particles, like plankton, that drift through the water. There are some tunicates, however, like the larvae shaped group, that use their tails to draw in water and food particles which then get stuck in mucus. Some hunt their food. And others live in symbiotic relationships with algae which may provide them food.

Most tunicates live a single year as adults. They are typically hermaphroditic but don’t self fertilize; instead, they’ll release their sperm into the water column simultaneously and then take in the water to fertilize the eggs that remain inside their bodies. The eggs are brooded inside the tunicate until they hatch.

The larval stage may last only a few days before they find a place to settle on a surface and metamorphose into an adult sometimes as quickly as 24 hours later! Tunicates can also reproduce asexually by budding and this is how tunicate colonies form. Tunicates may appear as individuals or in colonies. In size, the sessile types can reach up to 6.5 feet (2m) in length as a colony or 7.5 inches (2cm) as individuals. The tadpole-like, pelagic tunicates are generally really tiny at 0.2 inches (5mm) in length and they don’t form colonies. The other kinds of pelagic tunicates may appear as individuals or long chains that exist as a colony.

Tunicates have chemicals that make them distasteful to predators like other invertebrates and fish. Some tunicates can produce light which can confuse attackers! They are also able to eject water, hence the name sea squirt, and the pelagic forms use this ability as jet propulsion through the water column!

For more facts on tunicates, check out the link in the description. Thank you to Umber Temporis for today’s request! Give a thumbs up if you learned something new today, and thank you for watching Animal Fact Files!