Editing Graptolite (section)

=== Zooids ===
[[File:Zooidgrap.jpg|thumb|A hypothetical graptolite zooid inside its theca, reconstructed based on living pterobranchs|left]]A mature zooid has three important regions, the preoral disc or cephalic shield, the collar and the trunk. In the collar, the mouth and anus (U-shaped digestive system) and arms are found; Graptholitina has a single pair of arms with several paired tentacles. As a [[nervous system]], graptolites have a simple layer of fibers between the epidermis and the basal lamina, also have a ''collar ganglion'' that gives rise to several nerve branches, similar to the [[neural tube]] of chordates.<ref name="Satodevbio" /> Proper fossils of the soft parts of graptolites have yet to be found, and it is not known if they had pharyngeal gill slits or not,<ref>[https://books.google.com/books?id=pTygDQAAQBAJ&dq=graptolite+zooid+soft+pharyngeal+gill&pg=PA218 Fundamentals of Invertebrate Palaeontology: Macrofossils]</ref> but based on extant ''[[Rhabdopleura]]'', it is likely that the grapotlite zooids had the same morphology.<ref name="Maletzgp" />