Trigonotarbid hiding places
trigonotarbid moult parts
deutsche Version

What looks like modern artwork in Fig.1 is really moult parts of an early predatory arthropod known as trigonotarbid, most probably incidentally arranged so that the symmetry seems wondrous. Trigonotarbids are most easily recognized if incidentally seen as cross-sections with characteristic outline, as in Fig. 1.

Fig.1: Trigonotarbid moult parts, nearly symmetrically arranged. Image width 2.7mm.

Fig.2,3: Hollow straws of Horneophyton with trigonotarbid moult parts. Image width 5mm.

Trigonotarbid moult fragments inside hollow HorneophytonTrigonotarbid moult fragments inside hollow HorneophytonApparently these creatures usually crept into broken hollow straws of land plants, if available, as a protected hiding place for moulting (Figs.2,3). This is also suggested by the presence of moult parts of trigonotarbid legs in the hollow straw in Fig.3, only 1cm beside the one in Fig.2. Possibly the creatures chose places with many broken hollow straws as easily accessible hiding places. 
The granular structure in Figs.1,2 is not the remains of tissue but the result of spherulitic silicification in the watery fill.

Fig.4: Hollow straw of Aglaophyton with trigonotarbid moult parts.
Image width 5mm.

Trigonotarbid moult fragments inside hollow Horneophyton
Although Fig.4 is more confusing than the nearly circular sections in Figs.2,3, a few facts can be derived: It is an inclined section of a formerly hollow straw, successively filled as a result of various silicification processes, with a trigonotarbid moult cross-section as a conspicuous feature.
The level surface of the fill at the bottom of the moult indicates that there had been an intermediate fluid stage throughout the cavity of the moult, where precipitates had formed and settled into a heavy suspension with horizontal surface. Two small sections outside the big one seem to indicate that here, too, not the creature as a whole but only its moult parts had become silicified.
Another trigonotarbid "in hiding" is seen in Sociable trigonotarbids, there Fig.1.
Samples: Figs.1-3: Rh14/2 (6.3kg), obtained from Barron in 2005, Part1;  Fig.4: Rh9/58.2 (0.21kg), found by S. W. in 2004, Part2.

 H.-J. Weiss       2020
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