In their disposition they are either uniserial, biserial or multiserial.
Driesch, in which, however, the primitively uniserial arrangement becomes masked later by secondary torsions of the hydranths.
The polyp may then form a second bud, which becomes the starting point of a new system, the beginning, that is, of a new branch; and even a third bud, starting yet another system, may be produced from the same polyp. Hence the colonies of Calyptoblastea may be com plexly branched, and the bud ding may be biserial through out, uniserial throughout, or partly one, partly the other.
- Diagram of sympodial 18) there is formed a main stem budding, uniserial type, shown on tithe i ma in t emeafh r m s polyp in four stages (1-4).
By uniserial budding.
The pinnules never branch again, since in the uniserial mode of budding a polyp never forms a second polyp-bud.
Polyp 7 has proof sense, 1 o c oduced as its first bud, 8; as its second bud, a7, motion and nutriwhich starts a uniserial pinnule; and as a third t i on, until its bud I', which starts a biserial branch (I I'-VI') medusoid nature that repeats the structure of the main stem and and organization gives off pinnules.
Solitary polyps are unknown in this sub-order; the colony may be creeping or arborescent in form; if the latter, the budding of the polyps, as already stated, is of the sympodial type, and either biserial, forming stems capable of further branching, or uniserial, forming pinnules not capable of further branching.
- Hydrothecae sessile, biserial on the main stem, uniserial on the lateral branches or pinnules, which give the colony its characteristic feathery form; with nematophores.
The supposed hydrothecae may be present on one side of the axis only (monoprionid) or on both sides (diprionid); the first case may be conjectured to be the result of uniserial (helicoid) budding, the second to be produced by biserial (scorpioid) budding.
When they are arranged in uniserial or biserial rows the genital ducts open into or near the branchial grooves in the region of the pharynx and in a corresponding position in the post-branchial region.
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.
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.