The fact that choanoflagellates and collar cells of sponges resemble each other support the inference that chonoflagellates and sponges are sister groups.
Choanoflagellate are single -celled aquatic flagellate with single flagellum surrounded by a collar of microvilli. In addition choanoflagellate have a long interested evolutionary biologist due to their striking resemblance to collared cells of sponge.