Ref ID : 7690
A. Warren and P.G. Carey; Lorica Structure of the Freshwater Ciliate Platycola decumbens Ehrenberg, 1830 (Peritrichida, Vaginicolidae). Protistologica XIX(1):5-20, 1983
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The lorica structure of Platycola decumbens Ehrenberg, 1830 has been investigated using electron microscopy, cytochemistry and electron microprobe analysis. SEM revealed that the lorica possessed a characteristic border fringe and a distinctive aperture with well-formed lips. At high magnification the entire dorsal surface of the structure was seen to be covered by minute spheres, 30-60 nm in diameter, which exhibited no surface structure. They were distributed randomly but fairly uniformly over the dorsal surface including aperture lips and border fringe. When sectioned the lorica wall was seen to be composed of five or six layers of fibres, approximately 16 nm in diameter, embedded in an amorphous, electron dense matrix. Spheres were frequently seen to be detached from the lorica and there was no visible means of attachment. They were apparently without internal structure. Abraiding the wall with a fine stream of argon ions revealed the internal structure of the wall with fibres running predominantly transversely, although longitudinal sections through fibres were also obtained. 'Geoscan' analysis indicated that a major proportion of the wall was organic in nature but cytochemical staining proved ineffective in identifying specific compounds. Staining revealed the presence of ferric iron in the lorica which was subsequently confirmed by EDAX analysis of ultrathin sections. Heavy metals identified in the wall included iron and manganese. However, EDAX analysis of the wall spheres indicated that they were rich in silicon and phosphorus. The presence of heavy metals in the lorica was compared with the results of an analysis performed on river water from which the ciliates were isolated. The possible origin of wall spheres and the role of heavy metals in the strengthening of the test wall in a variety of protozoa is discussed.