Zoothamnium intermediumwas found attached to the exoskeleton of planktonic crustaceans, most of which were copepodsAcartia clausi.It formed branching colonies that consisted of zooids characterized by: 1) a bell‐like shape; 2) peristomial cilia that formed a single haplokinety raised above a double polykinety; and 3) unbranched annular striae, regularly distanced from each other by about 0.5μm, around the zooid circumference. Fully developed colonies contained also several roundish zooids that were identified as potential motile stages. In addition to colony members, free‐swimming dimorphic individuals were also occasionally observed: one type showed long trochal cilia and a scopula with a central area containing numerous protuberances; the other was characterized by short, stumpy cilia and a scopula endowed with a central finger‐like process surrounded by a pleated wrap. These free‐swimming individuals were tentatively identified as the microgamont and telotroch stage ofZoothamnium intermedium, respectively.