Nematoplexus - more details, more questions (2)
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screws10screw1Nematoplexus, first described in 1961 [1], appears to become ever more enigmatic as new details are discovered in the few fossil samples available now. (For an introduction see Part 1.)
However, there is one detail which is seen more clearly here: While the screw-like tubes usually "form a loose plexus and frequently appear to lie in lax interwoven coils" [1], thus making a confusing aspect, this sample offers the rare opportunity to see two of them separately. Incidentally, 5 turns of the screw are seen in either case: from outside in Fig.1 but from within in Fig.2 where one half of the thread has been cut off so that the ends of every half turn of the tube point out of the picture towards the observer.
The coherent tubes seen with several turns allow to confirm the characteristic rule stated earlier: thread diameter roughly equal to the pitch of the thread. (See
Rhynie Chert News 29.)

smallest Nematoplexus spiralFigs.1,2 (right): Screw-like Nematoplexus tubes, larger than those in [1]: tube diameter about 13Ám,
    thread diameter 130Ám.
Width of the images 1mm, same scale as in Part 1.

Fig.3 (left), detail of Fig.2 (below): Smallest spiral, apparently of different kind, thread diameter 30Ám.
    Image width 0.2mm, photograph by G.
Schmahl.  

Small spirals as those in Figs.3,6 may be confusing among the big ones as they resemble the wall patterns of Nematothallus tubes.  
basket of tubes
Another non-typical structure is seen in Fig.4. It looks like a piece of wire repeatedly bent into a tangle and placed immediately below the cut face. Some part has been cut off above left so that there seem to be two ends. Such kind of tangle has neither been seen with Nematoplexus nor with any other nematophyte. It differs distinctly from the "branch-knots" since apparently no purpose can be assigned to it while the branch knots can bring forth more than a dozen tubes emerging into any direction
 (See Part 1.)Nematoplexus big tubes
               
Fig.4 (left): Nematoplexus tube, 10Ám, bent into a tangle shaped as a coarse-meshed cage         without visible connection to other tubes. Width of the image 0.5mm.

Fig.5 (right): 8 big
slightly curved Nematoplexus tubes with smooth wall, 25Ám,
    indicating a common origin broken off here,
    and vanishing from sight in the depth,
2 thin tubes, 5Ám (?), on the left, one of them screw-like, 
thread diameter 90Ám,
    another one 
slightly curved.   
Width of the image 1mm, same scale as Figs.1,2.

These pictures vizualise part of the problems encountered when trying to make sense of the Nematoplexus
phenomenon. The screw-like tubes in Figs.1,2 are similar to but bigger than those in [1]. Big slightly curved tubes with smooth wall, seen in Fig.5 as a diverging bunch apparently coming from a big branch-knot in front of the picture plane, had not been seen in the type specimen [1]. One would be tempted to assign them to another species if there were not the fact that they are always found near or between the much smaller screw-like tubes. Since there are 8 of them diving into the half space behind the picture plane, one can assume that about the same number, not seen here, had come towards the observer before fragmentation of the chert layer had removed the big branch knot and exposed the tubes on the raw surface of the sample as seen here.
spiral
Fig.6 (left): Wall thickenings
of a big tube, short fragment, 33Ám wide, partially disintegrated.

As already mentioned in [1], also tubes of various sizes with helical or annular wall thickenings, not forming screws, are seen scattered as loose fragments or attached to branch-knots. Only very narrow tubes
(4-5Ám) with patterned wall have been seen emerging from a big branch-knot where the big smooth-walled tubes (Fig.5) come from: Rhynie Chert News 135. 

All presently availabe pieces of information about Nematoplexus taken together do not make a consistent view. As long as it is not known in which way the tubes of various type, shape, and size are mutually related, Nematoplexus and possibly other nematophytes have to be aptly called "enigmatic organisms". One should not be surprised if Nematoplexus would turn out to be based on some kind of symbiosis of nematophyte species.
Sample: Rh15/79 (0.27kg), obtained from Barron in 2014.

H.-J. Weiss      2016   2018    2020

[1]  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 x1.5)
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