On Micromastigotes and the evolution of the hypermastigont condition in the Parabasalida

Abstract

This study redescribes the genus Micromastigotes, Hollande and Carruette‐Valentin, 1971, a parabasalid flagellate symbiotic in termites, on the basis of light and electron microscopy. The genus Micromastigotes is characterised by possessing flagella bands which spiral around the anterior portion of the cell, the location of the nucleus and Golgi bodies at the base of the anterior flagellated area, and an axostyle, which runs the length of the cell. Individual flagella are derived from the central axis of the cell exiting perpendicularly, each is offset from the preceding flagellum by 12–18° thus forming a spiral band. Ultrastructurally, the flagella bases form a structure resembling a spiral staircase. Peltoaxostylar and preaxostylar fibres arise from the anterior most kinetosomes and the striated lamina forms a weakly undulating sheet directed posteriorly from each flagellum. Dense lamina and parabasal fibres are absent. Micromastigotes was originally classified as part of the Spirotrichonymphina and there are some similarities to other genera in this group, but Micromastigotes lacks a flagella gutter, a U‐shaped band at the base of the flagella composed of the striated and dense lamina, which is diagnostic of the spirotrichonymphines. The spiral pattern in Micromastigotes is not consistent with previous schemes for the development of a polymastigont condition in spirotrichonymphines suggesting that Micromastigotes represents an independent derivation of a polymastigont condition from a trichomonad‐like ancestor.