, a colorless choanoflagellate consisting of a cell body (protoplast) within an organic periplast or theca. A distinct collar of microvilli surrounds a single flagellum. Bacteria and debris are directed toward the base of the collar in currents generated by the flagellum. Food particles are engulfed by small pseudopodia from the protoplast just outside the collar of microvilli and then digested in food vacuoles at the posterior of the cell. A contractile vacuole and nucleus are seen anteriorly in this individual. This species with vase-shaped theca. From standing fresh water near Boise, Idaho. Phase contrast.