(subphylum Stomochordata, class Graptolithina)
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.
Subjects: Earth Sciences and Geography.