An order of graptolites that existed from the Middle Cambrian to the Lower Carboniferous. Most lived attached to the sea bed and were upright and bushy in appearance. They are many-branched, with numerous small thecae (see theca), in some connected by dissepiments. The stipes bear two kinds of thecae, autothecae and bithecae, opening from a continuous, closed stolotheca. There are concentric sheets of tissue in the lower part of the rhabdosome. The order contains three families: Acanthograptidae, Dendrograptidae, and Ptilograptidae.