The demise of a class of protists: taxonomic and nomenclatural revisions proposed for the protest phylum Myxozoa Grassé, 1970

Abstract

The phylum Myxozoa has been considered to comprise two classes, Myxosporea Bütschli, 1881 (primarily of fishes) and Actinosporea Noble in Levine et al., 1980 (primarily of aquatic oligochaetes). About 10 years ago it was demonstrated that the life cycle of Myxobolus cerebralis Hofer, 1903 (Myxobolidae: Platysporina) of salmonid fishes requires transformation of the myxosporean into an actinosporean stage in the oligochaete worm Tubifex tubifex (Tubificidae), and that the stage infective to fish is the actinosporean spore. This type of two-host life cycle has now been demonstrated or strongly implicated for 14 myxosporean species, belonging to 6 genera in 4 families. In light of these findings, the taxonomy of the Myxozoa is revised. We propose the following: suppression of the newer class Actinosporea and the order Actinomyxidia Štolc, 1899; and suppression of all families in the Actinosporea except Tetractinomyxidae. This family and its one genus, Tetractinomyxon Ikeda, 1912, are transferred to the order Multivalvulida Shulman, 1959 (Myxosporea). We also propose that actinosporean generic names be treated as collective-group names, thus they do not compete in priority with myxosporean generic names. Triactinomyxon dubium Granata, 1924 and Triactinomyxon gyrosalmo Wolf and Markiw, 1984 are suppressed as junior synonyms of Myxobolus cerebralis. The myxosporean stage of no other previously named actinosporean has been identified. Other actinosporean species are therefore retained as species inquirendae until their myxosporean stages are identified. A revised description of the phylum Myxozoa is provided that includes our proposed taxonomic and nomenclatural changes.

Actinosporean infections in oligochaetes in a river system in southwest Ireland with descriptions of three new forms

“…Since then, similar life cycles involving an actinosporean stage and an annelid host have been demonstrated for other myxosporean species (El-Matbouli & Hoffmann 1989, Ruidish et al 1991, ElMatbouli et al 1992, Großheider & Körting 1992, Benajiba & Marques 1993, Kent et al 1993, Yokoyama et al 1993a, 1995, Uspenskaya 1995, Bartholomew et al 1997, El-Mansy & Molnar 1997, Yokoyama 1997, Szé-kely et al 1998, Molnar et al 1999, Özer & Wootten 2000. These results, showing the actinosporeans to be stages in the life cycle of species of Myxosporea, led to the suppression of the class Actinosporea (Kent et al 1994).…”

A nested polymerase chain reaction for the detection of genomic DNA of Myxobolus cerebralis in rainbow trout Oncorhynchus mykiss

“…These developmental and spore stages were designated as myxosporean and actinosporean in their respective fish and worm hosts. The actinosporean forms, previously described as parasites of oligochaetes (Janiszewska 1955), were therefore united with the myxosporean forms for which infective stages for fish had previously been unknown (Corliss 1985, Kent et al 1994.…”

Myxozoa in Haeckels Shadow

“…For decades, specialists had been inching Myxozoa toward recognition as a phylum of multicellular animals [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Expectations ran so high that Myxozoa's "demise" as a protistan phylum was declared [18][19] even before deciding whether the myxozoans would belong to the Radiata or Bilateria. Molecular evidence ultimately proved decisive: Myxozoan "nematocyst" proteins (nematogalectins and minicollagens) were seen to be akin to cnidarian cnidocysts proteins [20].…”