Diagnosis: Deeply penetrating microboring with a single to multiple, basal, sack-shaped cavity oriented parallel to the substrate surface. Near the base of the cavity, a long, thin, filamentous tube extends straight into the substrate, ramifies distally and tapers to slender filaments.

Description: The traces are commonly found collapsed to the cast surface and partially etched samples are required to reveal their deeply penetrating nature (Fig. 3A–B). The trace is found to occur clustered in large numbers of up to several hundred individuals (Fig. 3H). At the base of the mature trace a double to multiple sack-shaped cavity up to 80μ minsizeis developed parallel to the substrate surface and is occasionally connected to the latter by numerous thin filaments (Fig. 3D). From near the base of the cavity, a thin (1–2μm) filamentous gallery extends straight and deep (up to several 100μm) into the substrate and may repeatedly ramify and in some cases build up a dense mesh with the distal parts of neighboring individuals (Fig.3B).Injuvenilespecimens,onlythethindeeplypenetrating filament is developed associated with a basal swelling a few micrometers in diameter (Fig. 3E). From this basal swelling, a single sack emerges during ontogeny, later bifurcating into double or multiple sack-shaped cavities, and in some cases even exhibiting a rosette-like appearance (Fig. 3G).