HRAP Online Encyclopedia

Tunicates

Out of all of the invertebrates found in the tide pools as Haystack, tunicates are the mostly closely related to the vertebrates. They’re even in the Chordata phylum! This means that a sea squirt is closer related to humans than crabs, sea stars, or even the intelligent octopus. Their bodies are covered in a tunic, or leathery skin, giving them their name. Tunicates can be solitary, colonial, or compound, meaning that they can live alone or in groups. Solitary tunicates are typically oval or irregular in shape and often have a stalk attaching them to the substrate. Colonial tunicates are social and found in groups of many individuals but they are not connected unless they share a base. Compound tunicates are similar to colonial tunicates in that there are many individuals but they are all covered in a shared tunic. All tunicates have two siphons for filtering water - an incurrent siphon and an excurrent siphon. Possibly the coolest fact about tunicates is their heartbeat. Every few minutes, tunicates will reverse the direction their heart is beating to change the direction of their blood flow. Why they might do this, science has yet to answer!