Morphology of the larva and ancestrula of Myriapora truncata (Bryozoa, Cheilostomatida).

During an essay to rear in aquarium some colonies of the Mediterranean erect bryozoan Myriapora truncata (Gymnolaemata, Cheilostomatida, Ascophorina, Myriaporidae) it was possible to study its larval and ancestrular morphology by scanning electron microscope (SEM) and by light microscope. The different phases of metamorphosis, giving origin to the preancestrula and the ancestrula, were also investigated. The larva of M. truncata is short-lived, lecithotrophic, and of the coronate type, with expanded corona and small pallial sinus (AEO/ps type, according to Zimmer & Woollacott; VB type, according to d’Hondt). Its morphology, life and metamorphosis appear very similar to those of other well described cheilostome larvae (Neocheilostomida sensu d’Hondt). But, unlike in the other known species of this group, the ancestrula derived from metamorphosis is an ‘ancestrular twin’, in which two zooids simultaneously develop; these can form in two possible reciprocal orientations (same—ipsolateral—or opposite—contralateral—in the direction of growth).