Nematoplexus - more details, more questions (1)
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Nematoplexus is one of the rarest and least understood objects in the Rhynie chert. It belongs to the obscure nematophytes, which go under the heading "Enigmatic Organisms" in [1], and is distinguished by tubes with a spiral or screw-like shape *. The number of samples with Nematoplexus found hitherto is very small. The type specimen discovered and described by A.G. Lyon [2] is probably the one which is seen on the website of Aberdeen University [3]. The characteristic features of Nematoplexus from that sample have first been stated in Rhynie Chert News 29. So it has come as a surprise that an own specimen, found in 2003, deviates in one of those features and shows a new one: Tube and thread diameters are distinctly larger, and weakly curved tubes seem to be somehow associated with the screw-like ones. This has also been observed with another sample, found in 2014 and described here.
 * Contrary to a statement in [3],
Nematoplexus is the only nematophyte with "spirally coiled" tubes.
Nemaotplexus tubes and branch knots
Fig.1,2: Nematoplexus tubes, spiralling or slightly curved, on the raw surface of a Rhynie chert sample. Width of the images 2mm.

Obviously the diameters of the wound tubes (10...13Ám) and threads (0.1...0.2mm) are larger than those of the type specimen [2]. Other features are the same, as right-handedness of the thread and pitch equalling diameter, unless the tubes had undergone later deformation.
Nematoplexus tubes
The enigmatic "branch knots", also known from other nematophytes, are dimly seen as two dark spots in the depth in Fig.1.
In addition to the screw-like tubes, slightly curved ones are seen in Fig.2 as about 10 cut-off ends and one longer part. If the latter were part of a circle, its diameter would exceed 1mm, which is 5 to 10 times the diameter of the screws.

The slightly curved tubes are seen scattered among the screws or well away from them but not very far. Hitherto they have never been found in a sample without spiralling tubes.
branch not of big tubesHence one may well assume that they belong together in some way although one does not know in which way.

Any doubt concerning the nematophyte nature of the big tubes is dispelled by the surprise discovery of their impressive "branch knots". Several have been seen on this sample but only one is clearly seen on a cut plane (Fig.3).

Fig.3 (right): "Branch knot" of big slightly curved Nematoplexus tubes, apparently the first such one ever seen.
 Width of the image 1.3mm, same scale as Figs.1,2.

Here, 4 of the tubes (19...22Ám) are cut off at their broadened base where they are seen as circular cross-sections of 30Ám. As an estimate, about 20 big tubes come out of the knot. Note also the few very thin filaments (4-5Ám) emerging from the knot, and an unrelated thin tube (9Ám) passing by.
big Nematoplexus strand
Fig.4: Nematoplexus tubes, nearly straight, two parallel big ones on the left, one of them 40Ám, thin one 11Ám.
Same scale as above.

Occasionally two nearly straight tubes run parallel to each other for some distance, apparently without spacing as in Fig.4, or several ones make a loose bundle, as indistinctly seen in the middle of Fig.2. (See also Rhynie Chert News 51 , Fig.2.)

The 9Ám-tube in Fig.3 above can be followed in the depth over a distance of 2.5mm whereby it appears that this tube is neither part of a circle nor of a big screw similar to the small screws. Hence one may guess that more of the weakly curved tubes are of this type.
Fragments of tubes with spiral or annular wall reinforcements,
similar to those in the type specimen [2], have been found in this sample, too.
As long as
Nematoplexus rhyniensis was known from the one fragmentary type specimen only, one could expect that the open questions would be answered by means of more finds. This expectation has not yet been fulfilled because Nematoplexus has remained very rare since its first description in 1961, and if present in a chert sample, the small patches with the tiny spiralling tubes are hard to find. The own finds have posed new questions without answering the old ones.
The present sample reveals a confusing variety of tubes, covering a wider range of size data than the type specimen [2] does. (There are erroneous size data in [1].) One would be tempted to assign them to different species if there were not the intriguing fact that they are found concentrated within regions of a few millimeters across. It is hoped that a consistent view will finally arise from combining the apparently incompatible observations.

H.-J. Weiss  
2015,  2016,  2017,  2020

[1]  T.N. Taylor, E.L. Taylor, M. Krings: Paleobotany, Elsevier 2009.

[2]  A.G. Lyon: On the fragmentary remains of an organism referable to the nematophytales, from the Rhynie chert, Nematoplexus rhyniensis
      Trans. Roy. Soc. Edinburgh 65(1961-62), 79-87, 2 plates.    (Scale error on Plate I Fig.1: not x19 but x1.8)
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