Comparative morphology of the euglenid pellicle. I. Patterns of strips and pores.

In anticipation that improved knowledge of euglenid morphology will provide robust apomorphy-based definitions for clades, transmission and scanning electron microscopy were used to reveal novel morphological patterns associated with the euglenid pellicle. In some taxa, the number of pellicle strips around the cell periphery reduces as discrete whorls at the anterior and posterior ends of the cell. The number of whorls at either end varies between selected euglenid taxa but is invariant within a taxon. The pattern of strip reduction associated with these whorls is shown to have at least three evolutionarily linked states: exponential, pseudoexponential, and linear. Two general equations describe these states near the posterior end of euglenid cells. Exponential patterns of strip reduction near the anterior end are described by a third equation. In addition, several euglenid taxa were found to possess conspicuous pellicle pores. These pores are arranged in discrete rows that follow the articulation zones between adjacent strips. The number of strips between rows of pores varies between taxa and displays a series of consecutive character states that differ by a power of two. The patterns of pores may not only have phylogenetical and taxonomical value but may provide morphological markers for following strip maturation during cytoskeletal reproduction.