Sponge , which possess -shaped, membranous 'collars' that are formed on .

These are the cells in sponges that resemble the protists known as . A flagellum is located within their collar-funnels, which serves to create that in turn bring into contact with the collars, resulting in phagocytosis.

The spongocoel of sponges, for example, is lined with choanocytes.