Sagenista and bigyra, two phyla of heterotrophic heterokont chromists

Abstract

Summary Heterokonta, Haptophyta and Cryptista are grouped together as the kingdom Chromista. As Heterokonta are considerably more diverse than the other two taxa, they have recently been raised in rank from phylum to infrakingdom, and subdivided into three phyla: the predominantly algal Ochrophyta (formerly subphylum Ochrista), and the purely heterotrophic Sagenista and Bigyra. The Sagenista comprise the classes Labyrinthulea (orders Thraustochytridiales and Labyrinthulales) and Bicoecea (bicoecids and the probably related flagellates Cafeteria and Pseudobodo, here designated anoecids and placed in the new order Anoecales). The Bigyra are characterised by a double ciliary transition helix and comprise three subphyla: Opalinata, which are all non-phagotrophic gut symbionts without peroxisomes (classes Proteromonadea and Opalinea; plus Blastocystis which lacks cilia and forms the basis for a recently established class Blastocystea); Pseudofungi, which are walled saprotrophs (classes Oomycetes and Hyphochytrea); and Bigyromonada (the phagotrophic zooflagellate Developayella Tong 1985, for which a new class Bigyromonadea, order Developayellales, and family Developayellaceae are created). This paper discusses the phylogeny, systematics, and evolution of the Sagenista and Bigyra and the evidence that they, like non-photosynthetic ochrophytes, evolved from photosynthetic ancestors by the loss of plastids and periplastid membranes. As the Bigyra are closely related to the Ochrophyta, and may have evolved from them, the two phyla have been grouped together as a superphylum Gyrista. Sagenista appear to be the sister group of Gyrista.