Peculiar tubelike elements, called by the writer tubothecae, occur on the specimens of a few genera of the Ordovician graptolites of the Tuboidea and Dendroidea. Tubothecae fundamentally differ from normal graptolite thecae in 1) a continuous increase, 2) irregular morphology and 3) lack of a fusellar microstructure characteristic of all graptolites. In view of such differences, the writer concludes that the tubothecae are elements strange to graptolite colonies. These are tubes of other animals which lived in association with graptolite colonies. Most likely, they were Annelida Polychaeta of the class Eunicea, which nowadays happen to be commensals of the corals Scleractinia and which secrete tubes similar to tubothecae. The remains of the Eunicea abundantly occur in the Ordovician along with the remains of graptolites and their associations might be realized as early as that epoch.