Practice question

Choanocytes are distinctive flagellated collar cells lining internal chambers and spongocoel each bearing single flagellum encircled by actin-rich microvilli forming collar filtering bacteria from water current generated by beating phagocytosing particles. Morphologically virtually identical to free-living unicellular and colonial Choanoflagellata possessing same design. Similarity supports hypothesis Metazoa evolved from choanoflagellate-like ancestor via colonial aggregation sharing adhesion and signaling genes. Such homology considered cornerstone evidence for animal monophyly placing sponges as sister to all other animals Parazoa with choanocytes totipotent able to differentiate into archaeocytes and gametes linking unicellular organization and multicellular life.