Ultrastructure and 3D reconstruction of a diplonemid protist (Diplonemea) and its novel membranous organelle

Abstract

Although diplonemid protists (Diplonemea, Euglenozoa) are among the most species-rich microeukaryotes in the ocean, many ultrastructural features of this lineage remain to be clarified. Using serial block-face scanning and transmission electron microscopy, we provide the whole-cell three-dimensional model of a previously undescribed diplonemid Lacrimia vacuolata sp. nov. For the first time, we were able to reconstruct a diplonemid cell in detail, including all its organelles and the flagellar and feeding apparatuses. By analyzing various stages of the cell cycle, we provide the first description of a diplonemid cell division, which is characterized by the disassembly of flagellar axonemes and the feeding apparatus and their further construction in the daughter cells. Moreover, we have identified a novel, ultrastructurally complex organelle, herein named the colv (Center for Organization of Layered Vesicles). We suggest that the colv is involved in food processing and membrane trafficking, and describe its close association with other components of the cellular digestive system.