Hyaloraphidium curvatum is not a green alga, but a lower fungus; Amoebidium parasiticum is not a fungus, but a member of the DRIPs

The unicellular heterotrophic protist Hyaloraphidium is classified with a f amily of green algae, the Ankistrodesmaceae. The only species that exists i n pure culture and that is available for taxonomic studies is H, curvatum, Comparative 18S ribosomal RNA sequence analyses showed that H. curvatum bel ongs to the fungi rather than to the algae. Within the fungi, H. curvatum p referentially clustered with Chytridiomycetes, Unlike Chytridiomycetes, H. curvatum propagates by autosporulation, and the presence of flagella has ne ver been reported, Transmission electron microscopy indicated that H, curva tum in some respects resembles Chytridiomycetes, but no elements of a flage llar apparatus were detected. The habitus of H. curvatum is unlike that of other fungi except the trichomycete Amoebidium parasiticum, The cell wall s ugar composition of H, curvatum was unique, but to some extent resembled th at of A, parasiticum. However, H. curvatum and A. parasiticum are not close ly related to each other according to 18S rRNA sequence data, Moreover, A. parasiticum clustered with protistan animals, the Mesomycetozoa (DRIPs), Co mbined molecular, ultrastructural and chemical data do not allow assignment of H. curvatum to any recognized clade of fungi. This suggests that H. cur vatum may represent an independent evolutionary lineage within the fungi.