Paraluffisphaera tuba Esteban et al., 2005
Diagnoses: Scale-bearing protists with the characteristics of the genus. Cells are oval, with a size range of 3 to 3.8 µm in length and 2.4 µm to 3 µm in width. The base scales are 0.4 × 0.3 µm; the elongate scales have a base scale and a trumpet-shaped tubular structure that is 1.5 µm long and projects upright from a basal elliptical scale. The cell surface is associated with one or several bacteria but the nature of this association is unknown.
Ecology: Soil. Type location: Montane grassland soil from Sourhope Research Station, Macaulay Land Use Research Institute, Natural Environment Research Council, near Kelso, Southern Scotland (UK).
Remarks: The description of Paraluffisphaera tuba is based on observations of shadowcast cells using transmission electron microscopy. Cells are ovoid and, in the specimens recorded, range in size from 3 × 2.4 µm to 3.8 × 3 µm. Esteban et al. could not observe flagella, pseudopodia or any other structures that might be noticeably involved in locomotion or feeding. However, the specimens appeared associated with bacteria of various sizes and with detrital particles. The cell surface of P. tuba is entirely covered with scales of two types:
(1) base scales, these are flat and elliptical, 0.4 × 0.3 µm in size, they interweave in all directions, and have a slit across the scale surface, with a thickened rim that gives the appearance of two lips in the centre of the scale;
(2) elongate scales, which seem to arise from the “open” slit of some of the base scales described above. The elongate scales are composed of two parts:
(a) a trumpet-shaped structure consisting of a tube (maximum 1.5 µm long and 0.06 µm wide in observed specimens) of cylindrical bore ending in a flared bell, with thickened rim. The tubular structures do not show any pattern or network on their surface apart from an inconspicuous transversal striation. The tubes seem to emerge through
(b) the labiated ‘open’ slit of base scales, and in most specimens they look as though they are in contact with or embedded in detritus particles and bacteria, but this might be a preparation-generated artefact. Most scales are of the base-type described above. The cell surface of P. tuba also appears associated with one or several bacteria whose size relative to the protist becomes immediately obvious. The nature of this association is unknown.