More nematophytes in the Rhynie chert
deutsche Version

Two species of the enigmatic "filamentous plants" had been discovered in the Rhynie chert and described as Nematophyton (1921) and Nematoplexus (1962). Another nematophyte, Pachytheca, known for a long time from other locations, had been found at Rhynie in 2003 and described in
Rhynie Chert News 1. More nematophytes have been found since: a flat one (2010) resembling but differing from Nematophyton, one of uncertain overall shape but with much bigger tubes (2005), another one with spirally coiled tubes (2009) but differing from Lyon's Nematoplexus in more than one way, a similar one showing monstrous "branch knots" of slightly curved big tubes (2015). chert with white clouds
A quite different aspect is offered by randomly arranged very thin and inconspicuous tubes or fragments thereof. Their variable curvature distinguishes them from aquatic fungus hyphae whose straight sections make a different aspect in the chert. The tubes are occasionally seen scattered within pale or white clouds in the usually darker chalzedony, suggesting the idea of a nematophyte connection. The idea was not pursued for the scarcity of fossil evidence until the tubes appeared abundantly on the cut faces of an olive-brown chert sample (Fig.1). 

Fig.1 (right): Rhynie chert with cloud-like formations, apparently former silica gel slightly older than other precipitates and deposits. Note the remains of small tubes faintly seen in a lump below the middle. Width of the picture 8mm.

  Fig.2 (above left): Randomly distributed tube fragments restricted to a part of chert appearing as a cloud. The cloud is thin on the right so that the yellow chert behind is shining through.
        Width of Figs.2-6: 1.4mm.

tubes tubes
  Fig.3 (above left): Similar as Fig.2, mineral debris on the right.                                                        Fig.4 (above right): Similar as Fig.2, no tubes in part of the cloud.   
tubes filaments
  Fig.5 (left): Similar as Fig.4.  
                                                                                                                               Fig.6 (right): Sample surface, longer tubes visible.                          

From the observation that the cloud-like areas seen on the surface and cut faces of some chert samples are free from the mineral precipitates abundantly present around them (Figs.1-3) it can be concluded that the clouds formed as lumps of gel before mineral silt formed in the water. The observation that tubes like those in the above pictures are restricted to the interior of the said clouds hints at a deeper connection. In the absence of additional information, several options are thinkable. The clouds could have been microbial colonies held together by organic slime or gel, then invaded by a tube-like organism feeding on them. As another possibility, the tubes could have produced the gel in the same way as nematophytes are supposed to do. Organic gel could have triggered the formation of silica gel and become replaced by the latter.
Alternatively, substances released by microbes or tubes could immediately have caused silica gel formation by changing the acidity of the water.
Most often the light-coloured clouds in chert seem to be "clean". This could mean that they had never been inhabited by tube-like organisms, or the latter are decayed and no more seen. This possibility is suggested by the observation of very faint remains of thin tubes in some chert samples.
There does not seem to be an easy interpretation of this type of fossil. The overall aspect of the tangle of randomly distributed irregularly curved tubes resembles that of unnamed nematophytes described in
Rhynie Chert News 13, 35 except for the very small tube diameters of 6-8-(10)Ám in this case, compared to 50-70Ám and 25-30Ám of the said nematophytes. Also the tubes in the above pictures seem to be less densely spaced. This, however, might be due to fast decay of part of the tubes, which could also explain the observation that there were lots of tube fragments. Tubes are seldom seen extending over some distance as in Fig.6.
Although a similarity to nematophyte tubes is obvious, the apparent absence of so-called "branch knots", a typical but not yet understood feature of nematophytes, raises doubts concerning a nematophyte affiliation. As an additionally confusing fact, this sample contains also a few tubes of different types whose possible relation to the tubes in the above pictures is questionable but cannot be ruled out (Figs.7,8).    
Figs.7,8: Some of the very few big tubes in this sample, among narrow ones of about 7Ám as in Figs.2-6,
diameters about 30Ám (with rings on the wall) and 20Ám, in bluish chalzedony surrounded by mineral debris.
(The white dots are not relevant.)
Width of the pictures 0.3mm, magnification twice as large as in Figs. 2-6.

The very few big tubes with diameters of about 15, 20, 30Ám are seen together with some narrow ones in smaller patches of bluish chalcedony separate from the larger whitish clouds. The combination of different types of tubes, including those with rings on the wall, is known from nematophytes. If the tubes in Figs.7,8 are nematophyte tubes, which they probably are, one may conclude that the narrow tubes in Figs.2-6 are nematophyte tubes, too. Hence, what has been described here is probably a new species of the enigmatic nematophytes which is not rare in the Rhynie chert but is easily overlooked.
The tubes have been discovered in 2015 on this sample Rh3/9 found in 1998.

H.-J. Weiss
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