Fine structure of Eutreptia pertyi (Euglenophyceae) and analytical ultrastructural characterization of the flagellar paraxial rods : functional and phylogenetic implications

The photosynthetic marine protist, Eutreptia pertyi (Prings.), has been suggested as the model "primitive green" organism in the Euglenophyceae. As a member of the order Eutreptiales, Eutreptia is characterized by two emergent flagella. Previous cytological and taxonomic studies have been based primarily on light-microscopic observations. This is the first ultrastructural investigation of the genus Eutreptia. For the species, E. pertyi, the following major cytological characters are reported: two nearly equal-length, heterodynamic flagella, ribbon-shaped chloroplasts that extend from a pyrenoid center, a relatively smooth pellicle, a presumptive vestigial cytopharynx associated with the canal cytoskeletal complex, and presumptive intracellular reservoirs for flagellar mastigonemes, termed "mastigoneme vesicles."

The flagella can be distinguished at the ultrastructural level by different complexities in an accessory component, termed the paraxial rod (PAR). Structural characterization of the PAR in the dorsal flagellum (PARl) shows one major substructural component -- the oblique filaments, which are arranged in reciprocal axes and give a "lattice like" appearance to PARl. Structural characterization of the PAR in the ventral flagellum (PAR2) shows 3 major substructural components-- oblique, horizontal and longitudinal filaments which are arranged in three axes and give PAR2 a paracrystalline "plate-like" appearance. The different substructures of PARl and PAR2 may contribute to heterodynamic flagellar motion.