In their disposition they are either uniserial, biserial or multiserial.
The thecae uniserial (monoprionidian) - t here is a gradation from earlier groups with many branches to later groups with only two; and from species in which all the branches and' their thecae are directed downwards, through species in which the branches become bent back more and more outwards and upwards, until in some the terminal thecae open almost vertically.
The Monograptidae, the branches are theoretically reduced to one, the polypary is uniserial throughout, and all the thecae are directed outwards and upwards.
In the genus Dendrograptus the gonothecae open within the walls of the ordinary thecae, and the branches present an outward resemblance to those of the uniserial Graptoloidea.
With very few exceptions, the integuments form imbricate scalelike folds arranged with the greatest regularity; they are small and pluriserial on the upper parts of the body and tail, large and uniserial on the abdomen, and generally biserial on the lower side of the tail.