A description of the testate amoeba Ovulina parva gen. nov., sp. nov. from coastal marine sediments

Abstract

A testate amoeba with organic test, isolated from sediments in the Firth of Clyde, Scotland, has been assigned to a new genus as Ovulina parva (Protista: Filosea) based on its unique light microscopic and fine structural morphology. The hyaline to amber test is ovate (~15×ll µm) with a terminal aperture that is either unadorned or with a shallow collar. Hyaline, long-tapering, pointed, sometimes branched, pseudopodia emerge directly from the aperture or from the periphery of a thin web of hyaline cytoplasm. The nucleus (~5 μm) with a central nucleolus (~2 μm) is located at the posterior of the cytoplasm. The fine structure of the test, examined by scanning and transmission electron microscopy, shows it is entirely organic with an irregular to granular surface. Scattered elongate pits (~1 μm long) without perforations are distributed irregularly on the surface. Ectoplasm is distributed within a fine fibrillar envelope lining the test. The endoplasm is ovoid and contains anteriorly located vacuoles enclosing densely-staining bodies with chromatin-like filaments which appear to be bacterial prey in late stages of digestion. This is further corroborated by light microscopic observations that bacteria are cleared from the surface of the culture dish within the circumference of the pseudopodia. The mitochondria (0.5–1.0 μm) have tubular cristae and some are located in the vicinity of peroxisomes (~0.5 μm) surrounded by a single membrane and with a finely granular matrix. Minimum doubling time in our cultures was 28.4 h, and the testate amoeba exhibits remarkable salinity tolerance growing in media ranging from 0 to 35% salinity.