The Stunning, Glass-Covered Resting Cyst of Maryna umbrellata (Ciliophora, Colpodea).

Maryna umbrellata (Gelei, 1950) Foissner, 1993 is a colpodid ciliate common in ephemeral water bodies. Pure cultures were established and the resting cyst studied by light and electron microscopy, protease digestion of thin sections, and various cytochemical reactions shown by colour micrographs. The cyst of M. umbrellata belongs to the kinetosome-resorbing (KR) type and has a conspicuous glass cover described by Foissner et al. (2009). It is 100 μm across and the about 13 μm thick wall, which amounts for half of the total cyst volume, consists of four distinct layers: (i) the about 6 μm thick pericyst, which is composed of glass granules embedded in mucoproteins, and of a basal layer consisting of glycogen tubules about 20 nm across; (ii) the about 140 nm thick, electron-dense ectocyst, which is not digested by protease; (iii) the about 6 μm thick mesocyst, which is distinctly laminated and made of proteins; and (iv) the thin, about 500 nm thick endocyst, which is structureless and consists of glycoproteins. The meso- and endocyst are highly elastic, reducing their diameter by 50% when the encysted ciliate is removed. The cyst contents is dominated by up to 7 μm-sized "spongy globules" consisting of an electron-dense, proteinaceous matrix burrowed by electron-lucent strands of glycogen, providing the cyst with a curious, white-spotted appearance in the electron microscope. The small lipid droplets have a proteinaceous centre. The cyst plasm contains proteins and unstructured mucosubstances, which stain with alcian blue, and thus possibly originate from the decomposed mucocysts. This study suggests that ciliate resting cysts are much more diverse than indicated by literature data.