Endocnidozoa, new cnidarian class?

Peter Schuchert schuchert at UBACLU.UNIBAS.CH
Thu Oct 3 09:31:25 CDT 1996


dear collegues
Would you like to discuss the following arguments?
Recently, Siddall et al (1995, see below) convincingly showed that the
Myxozoa are not protozoans but cnidarians. Most interestingly, the
molecular analysis showed a closer relationship to the only cnidarian genus
that has an intracellular parasitic stage: Polypodium.
Although not reliably resolvable at this stage, the clade (Myxozoa +
Polypodium) did not cluster within the Hydrozoa but together with the only
cubozoan species analyzed.
Polypodium is currently seen as a member of the Hydrozoa, more precisely
the Narcomedusae.
However, the inclusion of Polypodium in the Narcomedusae is not based on
any synapomorphies and is made only for lack of better solutions. Also the
inclusion within the Hydrozoa is not supported by any synapomorphy. The
medusa-like free phase of Polypodium has its gonads in the gastrodermis and
not in the epidermis (Raikova 1994) (epidermal gonads are an autapomorphy
of the Hydrozoa, see Schuchert 1993).
It thus seems that the the clade (Polypodium + Myxozoa) is not closely
related to the Hydrozoa and it probably constitutes a new class within the
Cnidaria. The autapomorphy for this clade would be endocytic parasitisms
(+support from 18S RNA sequence analysis). A new name for this clade could
be:

                                          Endocnidozoa.

The taxonomiy of the Cnidaria  (in traditional Linnean way) would therefore
look like as follows:

Phylum Cnidaria
               Subphylum Ametagenetica
                                                                   Class
Anthozoa
               Subphylum Metagenetica
                                                                   Class
Scyphozoa
                                                                   Class Cubozoa
                                                                   Class
Hydrozoa
                                                                   Class
Endocnidozoa


What do you think about this proposal?
with kind regards,
Peter


References:
Raikova-E 1994: Life cycle, cytology, and morphology of Polypodium
hydriforme, a coelenterate parasite of eggs of acipenserifom fishes. J.
Parasitology 80: 1-22.

Schuchert-P  1993: Phylogenetic analysis of the Cnidaria. Zeitschrift fuer
Zoologische Systematik und Evolutionsforschung 31(3): 161-173.

Siddall-M-E; Martin-D-S; Bridge-D; Desser-S-S; Cone-D-K  1995 : The demise
of a phylum of protists: Phylogeny of Myxozoa and other  parasitic
cnidaria. Journal of Parasitology 81(6): 961-967

see also http://www.vims.edu/%7Emes/myxozoa/myxozoa.html

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Peter Schuchert
University of Basel
Rheinsprung 9
CH-4051 Basel  Switzerland
fax 0041 61 267 34 57   tel 0041 61 267 34 78

http://www.unibas.ch/dib/zoologie/research/schuch.html
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