Journal of the Marine Biological Association of the United Kingdom 57: 285-301 (1977).

For this study, Choanoeca perplexa Ellis has been grown in culture and observations have been made using optical and electron microscopy. Sedentary cells can be distinguished by the presence of a flask-shaped theca, a long wide-angled collar and the absence of a flagellum. They divide to produce a naked swarmer with a single flagellum and a short, vertical-sided collar. Settlement of a swarmer to produce a sedentary cell involves the production of a theca and loss of the flagellum. Swarmers and sedentary cells are similar in microanatomy and agree in most respects with ultrastructural observations on other choanoflagellates. Adjacent to the base of the emergent flagellum is a supernumerary flagellar base which, in swarmers, is associated with a narrow cisterna of the ER. Ingestion of food particles by pseudopodia occurs actively in both swarmers and sedentary cells. These finding have been discussed in relation to other studies on choanoflagellates.