# The blood of tunicates such as the sea squirt is based on the rare element [[vanadium]] instead of the abundant [[iron]] used in other vertebrates, which would have required a complete re-tooling of its entire circulatory biochemistry <ref>http://www.earthlife.net/inverts/ascidiacea.html</ref>. | # The blood of tunicates such as the sea squirt is based on the rare element [[vanadium]] instead of the abundant [[iron]] used in other vertebrates, which would have required a complete re-tooling of its entire circulatory biochemistry <ref>http://www.earthlife.net/inverts/ascidiacea.html</ref>. |