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Keywords:

  • basal body complex;
  • cytoskeletal microtubule;
  • Euglenales;
  • feeding apparatus;
  • Phacus;
  • phylogeny

Phacus trypanon Pochmann is a photosynthetic euglenoid that is known to have typical characteristics of the Euglenales. The ultrastructure of P. trypanon was examined with particular attention being given to the striated fibers of both the basal body complex and feeding apparatus and microtubule arrangement. As in other euglenoids, the basal body complex was associated with the striated and fibrous fibers. The singlet microtubules at the reservoir level were arranged into doublets by a successive linkage of the existing adjacent microtubules at the transition level, and doublets were rearranged into a three-over-two pattern of cytoskeletal microtubules that were continuous with the subpellicular microtubules. The most striking feature of the feeding apparatus of P. trypanon was the prominent striated fiber that originated from the reservoir membrane and became arc shaped with electron-opaque bands at the lower canal level. The reinforcing microtubular band (MTR)/pocket of P. trypanon was associated with a prominent striated fiber that may act as a nucleating site for the semicircular microtubules, which surround the canal. The striated fiber and MTR/pocket are usually only found in those taxa that have a well-developed feeding apparatus and lack plastids; therefore, we speculate that the ingestion apparatus is functional in P. trypanon, which likely diverged in the early history of the photosynthetic green euglenoids.