Hufeisenwurm. Habitus und Bewegung der Actinotrocha. Wachstum und Differenzierung zur metamorphosebereiten Larve. Einzelheiten der Metamorphose zum adulten Tier. Habitus und Lebensweise der adulten Phoronis.

Actinotrocha branchiata Müller, a pelagic larvae, metamorphoses into a sessile adult, the Phoronis muelleri de Selys-Longchamps (Tentaculata). The metamorphosis takes about 10-15 minutes. The film shows the most important phases of this metamorphosis. At first there are documented some certain details necessary for the maturity of the larvae and the metamorphosing: the increase in size and in the number of tentacles, and the formation of a metasoma-diverticle, of the sense-organ and the enclosures of adult tentacles between the tentacles of the larvae.