B, Plant of the primitive Siphoneous Green Alga Protosiphon botryoides.
E, Vertical section of frond of the complicated Siphoneous Green Alga Halimeda.
In the Siphoneous family of Codzaceae the branches of the primitive cell become considerably interwoven one with another, so that a dense tissue-like structure is often produced.
Similar modes of growth occur among the Siphoneous Green Algae and also among the Red Seaweeds.
It consists of minute interwoven tubular filaments, and has been variously interpreted as possibly representing the sheaths of a Cyanophycean Alga, and as constituting a Siphoneous thallus of the type of the Codieae.
These forms, and others like them, go back to the Silurian and Ordovician; while Gyroporella, from the Permian, is another fairly characteristic Siphoneous type.
The gigantic Nematophycus, to be described below, has been regarded as having Siphoneous affinities.