Ultrastructure of Joenina pulchella Grassi, 1917 (Protista, Parabasalia), a reassessment of evolutionary trends in the parabasalids, and a new order Cristamonadida for devescovinid, calonymphid and lophomonad flagellates

AbstractThe parabasalids include parasites (e.g. trichomonads) as well as many hypermastigid flagellates which live in termites and other wood-eating insects and contribute to the cellulose-digesting capacity of those animals. A hypermastigid, Joenina pulchella Grassi, is shown to have a “flagellar area” composed of 1300 flagella, including three privileged basal bodies which have homologues in the trichomonads. The cytoskeleton includes preaxostylar fibres, two parabasal fibres and two atractophores with the parabasal fibres subdividing to form many parabasals. The microtubular rows of the pelta-axostyle system surround the flagellar area and converge towards a multispiralled axostylar trunk. On the basis of similarities of ultrastructure, joeniids and devescovinids are argued to be members of the same clade. Projoenia Lavette is in the sister group to Devescovina Foa and gives rise to the series Placojoenia Radek, Joenia Grassi, Joenina Grassi. Projoenia has a “flagellar area” as in the joeniids, but also a recurrent flagellum with a paraxonemal fibre and a cresta as does Devescovina. Projoenia has a parabasal fibre twisted around the axostyle, as well as a multispiralled axostyle. In Placojoenia, Joenia and Joenina the recurrent flagellum is absent or reduced to the basal body as is the cresta; the parabasal apparatus becomes multibranched. The classical Hypermastigida is in need of major revision. Parabasalids such as Lophomonadidae, Joeniidae, Deltotrichonymphidae, and possibly Rhizonymphidae and Kofoidiidae, collectively the lophomonads, have conserved the trichomonad/devescovinid organization and have a trichomonad-like morphogenesis involving only the privileged basal bodies and attached fibres. They can be distinguished from the rest of hypermastigids and should be classified with the Devescovinidae and Calonymphidae in a large clade — the Cristamonadida (new order). The remaining hypermastigids (the Trichonymphina and Spirotrichonymphina) have a rostrum which separates in two hemi-rostra at division, form a sister group to all other parabasalids and are not closely related to the remainder of the hypermastigids