Euglenoid flagellar root systems : ultrastructure and phylogenetic significanc

The ultrastructure and arrangement of flagellar root systems have become increasingly important indicators of phylogenetic relatedness among the algae. In this ultrastructural study, the flagellar roots of two euglenoid organisms, Entosiphon sulcatum and Eutreptia pertyi, are examined in detail and are compared with fragmentary published information available on other euglenoid roots, and with the more intensively studied bodonid flagellar root systems. This is the first systematic investigation of euglenoid roots; names for the roots are applied on the basis of their location in the basal body complex where they originate. The euglenoid root pattern consists of three microtubular flagellar roots, one on either side of the two functional basal bodies and one between them, nearer to the basal body of the posterior flagellum. All three roots extend anteriorly along the reservoir margin. The dorsal root is associated with an electron-dense plate and a band of stigma-related microtubules, which are continuous with the canal and pellicle microtubules. The intermediate root originates between the two basal bodies and has a predictable spatial relationship with the posterior flagellum. The ventral root originates near the posterior flagellum and becomes incorporated into the supporting structure of the cytopharynx. The dorsal, intermediate, and ventral euglenoid roots correspond to the dorsal connector, ventral fiber, and reinforced microtubules, respectively, of the bodonids. The similarity of euglenoid and bodonid flagellar root patterns lends strong support to the recently proposed euglenoid-kinetoplastid supergroup, the Euglenozoa.