Taxonomy and phylogeny of heliozoa: should this taxon exist in modern classification of protista?

摘要

Heliozoa Haeckel, 1866, are considered to be a polyphyletic cluster composed mainly of unrelated taxa united by similar external appearance of their representatives, determined by their common ecological niche of passive benthic predators having food capturing apparatus in the form of an extensive radial system of granuloaxopods, which serve for arresting and immobilizing small motile prey particles in a large volume of water. The following natural taxa are included in Heliozoa: Centrohelida Kuhn,Actinophryida Hartmann, Desmothoracida Hertwig et Lesser, Gymnosphaerida Poche, Ciliophryida Fevre-Chevalier, Pedinellales Zimmermann et al., and Dimorphida Siemensma. Discocristate filose amoebas, Rotosphaerida Rainer, are also traditionally attributedto Heliozoa; Centroheliozoa Durrschmidt et Patterson are regarded as a separate taxon of division rank, including two classes--Centrohelea Cavalier-Smith and Gymnophorea Mikrjukov et Mylnikov. We propose to consider Actinophryida, Ciliophryida, and Pedinellales to be taxa of subclass Pedinellidae Cavalier-Smith (together with the order Rhizochromulinales O'Kelly et Wujek) belonging to straminopiles of the phylum Ochrophyta Cavalier-Smith. We regard Actinophrys as a direct descendant of Ciliophrys, whichhad developed a more powerful axopodial apparatus in order to intensify the phagotrophic feeding and had lost the flagellum. We suppose the position of the heliozoan orders Dimorphida, Desmothoracida, and Gymnosphaerida to be among the heterotrophic amoebo-flagellates of the phylum Sarcomonada Cavalier-Smith, stat. n., within a new class Cercomonadea classis n. (with the order Cercomonadida Mylnikov as a type group). This class, Cercomonadea, is a sister group to the class Mycetozoa de Bary and to someother amoebo-flagellate taxa. There exist enough arguments to place rotosphaerids within the subkingdom Eozoa Cavalier-Smith in the same rank as the other macrotaxa of this subkingdom, i.e., in the rank of phylum Nucleariomorpha phylum n. In the classification of protists that we propose, the heliozoans form four clusters of groups belonging to different macrotaxa of division rank.