CYTOMORPHOLOGICAL CHARACTERS OF POLYPODIUM HYDRIFORME AND PROBLEMS OF MYXOZOAN AND CNIDARIAN
PHYLOGENY
E. V. Raikova
Institute of Cytology RAS, St. Petersburg, Russia;
e-mail: Raikova@swipnet.se
The present review analyses cytomorphological characters of the parasitic cnidarian Polypodium hydriforme,
discriminating between those of bilateral (triploblastic) animals, common characters shared with the Myxozoa, and the unique
characters of this species. Phylogenetic position of the group of parasitic cnidarians and of the class Polypodiozoa is discussed.
A conclusion is made that the cytomorphological characters as well as 18S rDNA analysis of P. hydriforme and Myxozoa
justify establishment of a new taxonomic group (a clade) of parasitic cnidarians (Endocnidozoa) uniting Polypodiozoa and Myxozoa
(Zrzavy, Hypsa, 2003). The unique characters of P. hydriforme suggest that the phylum Cnidaria is more diverse than
commonly supposed, and that P. hydriforme is not an aberrant cnidarian species but a relic organism, which might
originally belong to the cnidarian class Polypodiozoa, which underwent reduction in the course of adaptation to parasitism.
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