Graptolite morphology

Graptolites had a relatively simple construction, and this is especially true for the planktic graptoloids. Benthic species built branches, or stipes, made of several types of cups, or thecae, in which the zooids lived. These thecae stick out from the stipe at regular intervals, and when a stipe is sectioned a bundle of thecae can be seen. The colony, or rhabdosome, of the graptolite was constructed from a set of stipes arranged in characteristic patterns. In benthic graptolites this pattern is...