What does the presence of choanocytes suggest about the evolution of sponges?

There are a group of protists, the choanoflagellates which are structurally similar in having a flagellum crowned by microvilli. One group, Proterospongia, is colonial and shows limited cell specialization. We see single celled organisms, colonial organisms, and organisms with specialized cells and distinct structures, all possessing a common element. Genetics has shown that choanoflagelates are related to animals.