New finds of Nematoplexus in the Rhynie chert

Nematoplexus rhyniensis, detail from the type specimen

Apparently there is only one fossil in the Rhynie chert which can immediately be recognized by its peculiar structure even from small parts: Nematoplexus rhyniensis [1] is mainly made up of a tangle of wound tubes which looks chaotic at first sight but surprisingly reveals more than one sign of orderliness (Fig.1). Ignoring a less conspicuous minority of irregularly curved tubes with spiral wall thickenings, one can state the following:

(1) The tubes are wound into a rather regular thread ...
(2) ... which is always right-handed.
(3) The diameter of the thread lies between the bounds of 0.08 and 0.12 mm.
(4) The pitch of the thread seems to roughly equal its diameter.

One may wonder why the features (1) to (4) were neither included into the diagnosis of the species in [1] nor had been noticed by others.

Fig.1: Nematoplexus rhyniensis, detail from image in [2], probably of the type specimen in [1]. Width of the picture 0.35mm.

Fig.2 (below left): Nematoplexus from own sample Rh9/86, natural fracture face with wound filaments seen within the chalcedony, resembling those in Fig.1 except for their size. Width of the picture 0.7mm, note that this is twice the width of Fig.1.
big Nematoplexus, own find

There are a few more species consisting of a felt of tubes, like the still unnamed one described in Rhynie Chert News 13 , but none of them shows threads (*). They are called nematophytes, which means filamentous plants. They clearly differ from the various extant types of filamentous algae. What they may have in common is some kind of gel binding the tubes into a larger entity and keeping out floating debris and aquatic creatures. Nematoplexus rhyniensis was described by A.G. Lyon on the basis of incompletely recovered fragments of a shattered chert sample of a rare variety without the usually abundant remains of terrestrial plants. (Fossiliferous chert should never be hit.)
The present sample, too, does not contain land plants but the green alga Palaeonitella instead, also the aquatic crustacean Castracollis, which has been repeatedly found recently together with flooded land plants. (See Rhynie Chert News 24, 34, 43.) The present specimen of Nematoplexus (Figs.2-4) has been discovered by inspecting the smooth surface of a chert layer fragment of 0.28kg. The typical coils and "branch-knots" described in [1] are scattered here over a patch of about 5mm across, which is probably not representative of the whole. big Nematoplexus, right-hand thread

Figs.3,4 (right): Details of this Nematoplexus specimen, same magnification as Fig.1.

Note that the tube below right in Fig.3 does not dive below the other one as it might seem: It comes out of the surface and thus is not seen where it had been placed over the other one before it was removed by the crack which created the surface. Considering this, one sees three wound tubes with right-handed thread. Four such tubes, beside a few odd ends, are revealed by careful inspection of Fig. 4.
(Figs. 2-4: pictures taken by C. Kamenz.)

As seen in Figs. 2-4, this specimen, too, shows the feature of right-handed thread. By taking into account the foreshortening of the coils in these pictures, it appears that the feature of pitch roughly equalling thread diameter is also realized here.
What distinguishes the present specimen from the type specimen of Nematoplexus rhyniensis in [1] is the conspicuously larger structure size.

Sample	Tube diameter [µm]	Thread diameter [µm]
[1,2] [3] Rh9/86.1,2 (2003) Rh9/86.2 Rh6/73.2 (2003) Rh15/79.1,2 (2014) Rh15/79.3 Rh15/79.3 Rh15/79.4 Rh6/102 (2003) Rh5/3.2A (2001)	(7)-8-9-(10) ? 10 - 15 6 ~ 15 10 - 14 13 4 7 11 9 ?	80 - 120 80 - 120 140 - 210 70 ~140 100 - 200 130 30 75 160- 200 90

Among the often numerous regularly wound tubes, or scattered throughout the same chert sample, there may be irregularly curved ones with annular or spiral wall thickenings. They have not been considered here.
With the presently sparse fossil evidence of Nematoplexus it seems not justified to regard the bigger variety as a new species. This may be reconsidered as soon as more finds revealing other details become available.
The sample Rh9/86 had been first presented on a friend's website where it is still seen [4]. For recent observations on the same sample see Rhynie Chert News 51, 106.
The statement in [2] that "Nematophytes appear to generally comprise networks of intertwined spirally coiled tubular cells" is clearly not true: All other nematophytes found hitherto in the Rhynie chert do not have spirally coiled cells: See Rhynie Chert News 1, 13, 30, 35, 36, 38, 40, 46, 98, 99. Apart from the Rhynie chert, other nematophytes, too, do not seem to have spirally coiled cells, hence Nematoplexus seems to be the only species with this peculiarity.

Addendum 2016: Meanwhile, Nematoplexushas been found in three more samples. The above table has been extended accordingly. Note the variety of tubes in the sample Rh15/79. Weakly curved tubes of Nematoplexus have been discovered recently among the screw-like ones: See Rhynie Chert News 51, 71, 102. They have not been included into the above table.
Annotation 2017: Additional information (also year of find) has been put in and the headline has been modified. (Old headline: Another enigmatic Nematoplexus from the Rhynie chert.)
Annotation 2018: The suggestion in [5], Nematoplexus "may represent the permineralized equivalent of Nematothallus" is certainly not true. The unique and distinctive feature of Nematoplexus, the screw-like wound tubes, have not even been mentioned in [5]. The alleged branch knot in [5], Fig.6.10, does not show any similarity with the various branch knots found in own samples, see Rhynie Chert News 126. The tubes of Nematoplexus in [5], Fig.6.9, are much too large.
For a graphical representation of part of the information in the above table see Rhynie Chert News 122.
Annotation 2020: The smallest tube in the above table has been deleted: probably erroneous, as pointed out in 102, there Fig.3.

H.-J. Weiss 2009, 2013, 2016, 2017, 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)
[2] www.abdn.ac.uk/rhynie/nemato.htm
[3] S.R. Fayers, N.H. Trewin: A review of the palaeoinvironments and biota of the Windyfield chert.
Trans. Roy. Soc. Edinburgh Earth Sci. 94(2004 for 2003), 325-39.
[4] H. Steur: www.xs4all.nl/~steurh/
[5] T.N. Taylor, E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009, p.183.