Taxonomy and phylogeny of heliozoa. II. The order dimorphida siemensma, 1991 (Cercomonadea classis n.): Diversity and relatedness with cercomonads

A taxonomic review of dimorphid helioflagellates, and the analysis of the p hylogenetic position of this group among other protists are performed. The generic name Dimorphella Valkanov, 1928 is considered as a junior synonym o f Dimorpha Gruber, 1882, whilst its single member is transferred to Dimorph a as the second, most widespread, species of this genus - D. elegans (Valka nov, 1928) comb. n. D. floridanis Bovee, 1960 is a junior synonym of D. mut ans. The marine D. sabina Ruinen, 1938 is not a dimorphid. Three species ar e considered in Tetradimorpha Hsiung, 1927; they are T. radiata Hsiung, 192 7 (the type-species), T. tetramastix (Penard, 1921) Siemensma, 1991, and a new species, T. pterbica Mikrjukov et Patterson, sp. n. described from a ma ngrove swamp in the northern Australia. A brief report and a scheme of the fine structure of T. pterbica is adduced. The marine T. marina Fenchel et a l., 1995 is regarded as a member of a separate, monotypic genus Pseudodimor pha gen. n. not belonging to dimorphids; it can be circumscribed as "bi- or tetraflagellate helioflagellates with axopodial axonemes ending at the nuc leus". Diagnoses of 2 dimorphid genera and 5 species, and a key to them are given. The analysis of the biology and cell structure suggests that the or der Dimorphida Siemensma, 1991 can be placed among amoeboid heterotrophic b iflagellates of the phylum Sarcomonada Cavalier-Smith, 1993, stat. n. insid e a new class Cercomonadea classis n. together with orders Cercomonadida Po che, 1913, Gymnosphaerida Poche, 1913, and Desmothoracida Hertwig et Lesser , 1874. Members of this new class could be briefly characterized as "tubulo cristate heterotrophic amoeboid biflagellates with a clear interphase micro tubule organizing centre (MTOC), nucleating cytoplasmic and pseudopodial mi crotubules, which appears as a separate electron-dense organelle at the for epart of the cell or by a material at the nuclear envelope".