Phylogeny of Diplonema ambulator (Larsen and Patterson) : 2. Homologies of the feeding apparatus

Abstract

Summary The ultrastructure of the flagellar apparatus of Diplonema ambulator was determined to investigate the phylogenetic placement of this genus. Two flagella insert into a pocket and bear distal and proximal transitional plates. The basal bodies are linked by a connecting fiber and are associated with three microtubular roots. A three-membered dorsal root attaches to the dorsal basal body and ascends along the flagellar pocket. An intermediate root is composed of five microtubules where it attaches to the ventral basal body (Vb). As it ascends along the flagellar pocket, two additional microtubules become associated, producing a 6 + 1 configuration. A four-membered ventral root attaches laterally to the Vb and extends into the cytoplasm. The flagellar pocket is lined on one side by an independent band of microtubules which are reminiscent of the bodonid MTR. The presence of three asymmetrically arranged microtubular roots, transitional plates similar to those in the flagella of kinetoplastids, and an MTR-like band further support the relationship of Diplonema with the Euglenozoa. However, the absence of paraxonemal rods and flagellar hairs as well as the unique mitotic chromosome behavior and peculiar mitochondrial cristae structure suggest that Diplonema may have undergone substantial independent evolution since its point of divergence.