(phylum Hemichordata, class Pterobranchia)
An order of colonial animals in which zooids are pectocaulus. The mesosoma bears one pair of arms. The gonads are unpaired, with a single gonadial opening on the right side. There are no branchial pores. The skeleton (coenoecium) is built of an irregularly branching system of chitinous tubes composed of regular growth bands which are clearly defined by transverse growth lines. Their first known occurrence is in the Late Cretaceous.
Subjects: Zoology and Animal Sciences.