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, (image turned): Smallest spiralling tube, thread diameter 30Ám, tube about 4Ám.
    Image width 0.2mm, photograph by G.
Schmahl.        (See Annotation 2020 below.)

In addition to the big surprises, the big slightly curved tubes shown in Part 1 and to be discussed here once more, there have been big surprises small in size. One of them is the tiny screw-like tube in Fig.3,  the only one of its kind, slightly disarranged here. There is no indication in which way it might be related to the "normal" screws. Its thread is even narrower than the tube with spiral and annular wall pattern in Fig.6. Hence, one must take care not to confuse the tiny screw-like tubes with the spiral wall patterns of similar size. (See Annotation 2020 below.)
basket of tubes
Another non-typical structure is the one 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 them while the branch knots can bring forth more than a dozen tubes extending into any direction from the
enigmatic interior of the knots(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, all of them apparently coming from a big branch knot 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]. The tiny spiral in Fig.3 does not seem to fit anywhere. Big slightly curved tubes with smooth wall, seen in Fig.5 as a diverging bunch apparently centered at a big branch knot above 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 fracture of the chert layer had removed the big branch knot and exposed the tubes on the raw surface of the sample as seen here.

spiralFig.6 (left): Big tube with wall thickenings, short fragment, 33Ám wide, partially disintegrated.

The matter is complicated by the fact that there are miniature screw-like and very thin slightly curved tubes as seen in Figs.3,5.
A more conspicuous complication, as already mentioned in [1], comes from the tubes of various sizes with helical or annular wall thickenings (Fig.6). They do not form screws, are most often seen scattered as loose fragments but are also seen attached to the smaller kind of branch knots. Apparently they are not related to the big branch knots where the big smooth-walled tubes come from (Fig.5).

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.

Addition 2018: Fig.3 has been added and the figures have been re-numerated.
Annotation 2020: Apparently the warning against confusion has been justified: Now it seems that Fig.3 shows wall thickenings of a big tube, similar as those in
Rhynie Chert News 151.
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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