Fine Structure Observation of Feeding Behavior, Nephroselmis spp.-derived Chloroplast Enlargement, and Mitotic Processes in the Katablepharid Hatena arenicola

The difficult-to-cultivate katablepharid Hatena arenicola ingests green algae, Nephroselmis spp., and temporarily retains a Nephroselmis-derived cell compartment (kleptochloroplast), including a chloroplast within a phagocytotic vacuole. H. arenicola has a unique life history; during cell division, the Nephroselmis-derived cell compartment is only inherited by one of two daughter cells. However, the detailed morphological transition of the Nephroselmis cell to a kleptochloroplast and the mitotic process of the host cell remain unclear. Herein, we observed feeding behavior, enlargement of the Nephroselmis-derived chloroplast, and mitotic processes in H. arenicola using light and electron microscopy. During feeding behavior, H. arenicola peeled off the cell coverings and flagella of the Nephroselmis cell, which selectively accumulated in a vacuole separate to one containing a Nephroselmis cell body. An obvious nucleolus, but no heterochromatin was observed in the Nephroselmis-derived nucleus during the chloroplast-enlarging process, while compressed heterochromatin was explicitly observed in the nuclei of free-living Nephroselmis cells. The cell membrane of an ingested Nephroselmis cell disintegrated during enlargement of the Nephroselmis-derived chloroplast. The process of mitosis in H. arenicola was very similar to that of other katablepharids and cryptophytes.