The reproductive organs of Rhabdopleura have but seldom been ob served.
In Rhabdopleura each zooid forms its own delicate tube composed of a characteristic series of distinct rings.
While in Rhabdopleura the buds remain in organic continuity with the parent, in Cephalodiscus they become free at an early stage, and the coenoecium accordingly contains a number of separate individuals.
Phoronis has long been regarded as a possible ally of Rhabdopleura (see Pterobranchia); and Masterman (to) has attempted to demonstrate the existence in Actinotrocha of most of the structures which occur in the Pterobranchia.
No less than twelve species, referred to three sub-genera (Demiothecia, Idiothecia, Orthoecus), have now been described; but it is at present uncertain whether more than a single species of Rhabdopleura is valid, although several specific names have been suggested for specimens from different localities.