Problems of structure and biology in a large collared flagellate ( Diaphanoeca grandis Ellis) from arctic seas

On the basis of wild material processed into dry who mounts immediately following collection in two arctic localities (Hudson Bay and under sea ice in North Alaska), new insight has been obtained into lorica structure and development in Diaphanoeca grandis (Choanoflagellata) by means of scanning electron microscopy supplementing transmission electron microscopy and light microscopy. The more important new findings include demonstration of tectiform replication and of the two-layered nature of the lorica wall, the outer layer being limited throughout to longitudinal costae only. Details of transverse costae and of the fibrillar or membranous components involved in suspension of the protoplast are also described and illustrated. Outstanding problems, notably those involved in nutrient uptake, are discussed and the nature of the observations most needed to resolve them indicated. A revised description of the species replaces a summary.