Rhabdopleurida
Rhabdopleurida
Order of hemichordates in the pterobranchian class
Rhabdopleurida is one of three orders in the class Pterobranchia, which are small, worm-shaped animals, are the only surviving graptolites. Members belong to the hemichordates.[2][3] Species in this order are sessile, colonial, connected with a stolon, living in clear water and secrete tubes called tubarium. They have a single gonad, the gill slits are absent and the collar has two tentaculated arms.[4] Rhabdopleura is the best studied pterobranch in developmental biology.[5] Rhabdopleura is the only extant graptolite.[6][7]