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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

[ref. ID; 7466 (Foissner, 1999)]

Grossglockneriids are a particular group of soil ciliates with a minute (< /_ 4 um) feeding tube in the centre of the small, flat oral field. The tube is used to perforate the cell wall of yeasts, fungal hyphae, and spores to take up their contents. No other food can be ingested because the paroral and adoral ciliature are weakly developed and the minute, highly specialized feeding tube is the sole feeding organelle (Foissner 1993). Although globally distributed and present in almost every soil sample, grossglockneriids were only discovered in 1980 (Foissner 1980). Very likely, they were misidentified or not identified at all previously. Foissner (1980, 1993) recognized the close relationship between the strictly mycophagous grossglockneriids and the classical, bacterivorous and predaceous colpodids, such as Colpoda and Bresslaua, and thus assigned them to this group. Recently, this has been confirmed by SSrRNA sequence data (Lynn et al. 1998). The grossglockneriids are a small group of six, described species distributed over four genera.

Taxonomic ranking of grossglockneriids; Foissner (1980, 1993, 1994) assigned ordinal rank to the grossglockneriids because of their unique and complex feeding tube, which is used to penetrate the cell walls of fungal hyphae and conidia and take up their contents. The general organization (Foissner, 1993) and somatic ultrastructure (Aescht et al. 1991) are very similar to those found in members of the order Colpodida. Recent data (Lynn et al. 1998) on the SSrRNA gene sequences of Pseudoplatyophrya (a typical grossglockneriid) and Bresslaua (a typical colpodid) have confirmed the sister group relationship proposed by Foissner as early as 1980 (1980). However, the sequence data also show that the molecular distance between two other colpodid sister taxa, the bryometopids and bursariomorphids, is considerably larger than that between Bresslaua and Pseudoplatyophrya. Thus, Lynn & Small (1997, and pers. commun.) classified the grossglockneriids only as a family of the Colpodida. I agree with Mayr (1975) and others that tax ranking should be practical and reflect the significance of traits. The grossglockneriids, whose complex feeding tube probably did not evolve by a single, simple evolutionary process and which is associated with a dramatic change in the ecology and physiology of the organisms, entered a new adaptive zone and have divesified as eight distance species (very likely, some more have not yet been discovered) with a variety of specializations. Thus separation at ordinal level seems appropriate, so much the more as the whole colpodids have class rank (Lynn et al. 1997).