Stephanopogon

Stephanopogon is a peculiar marine protozoan. It closely resembles certain ciliates and was originally classified with them, but is now considered a flagellate. The cell is somewhat flattened, with multiple smooth flagella arranged in rows running from the front to the back, and has an anterior mouth supported by rods. They feed on bacteria, diatoms, and other smaller organisms. There are 2-16 nuclei, but they are not differentiated into macronuclei and micronuclei as occurs in ciliates.

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Because the nuclei are homogeneous, Stephanopogon has been regarded as an evolutionary intermediate between the ciliates and other protozoa, and possibly an ancestor of the animals as well. However, Corliss and Lipscomb showed that it is not related to ciliates, and lacks their complex pellicle and infraciliature^[1]. Stephanopogon has mitochondria with discoid cristae and lacks dictyosomes, and so is probably related to the Percolozoa, but its exact position is still uncertain.

References

1. ^ Corliss, J.O. and Lipscomb, D.L. (1982). "Establishment of new order in kingdom Protista for Stephanopogon, long-known "ciliate" revealed now as a flagellate". Journal of Protozoology 92: 294.