Ultrastructure of the tuboid graptolite tubotheca

The wall of the tubotheca of the tuboid graptoliteEpigraptus eisenacki Mierzejewski has been studied with TEM. It was found that the tubothecal wall is composed of the cortical tissue which differs only slightly from the same tissue described in Dendroidea andMastigograptus sp. In addition a giant tubotheca inDiscograptus schmidti Wiman has been examined with SEM. The tubothecae studied seem to confirm a non-graptolite nature of the organisms living in them, while providing evidence that the tubotheca wall was a genuine graptolite structure overgrowing these organisms.