Diagnosis: Borings comprised of two basic morphotypes and the transitions between them. The system spreads by branching tunnels, which radiate underneath the substrate surface from a single point of entry. The system deepens starting in the central portions by developing elongate lateral swellings perpendicular to the radiating tunnels and to the surface of the substrate.

Description: The boring starts from a single point of entry and expands radial forming a shallow network system which is circular in outline and expanding. The initial growth produces cylindrical tunnels, later expanding into deeper penetrating sacs, which empty to the substrate surface. The boring consists of two principal modules connected with transitional forms. Module 1 – tunnels: Tunnels cylindrical in cross section of relatively constant diameter of 4.5 ± 0.8 μm (25 measurements) branching at various angles, formed by an intertwined network of septate filaments. This module predominates in the early stages of growth and is responsible for lateral expansion of the system. The mature systems retain this early module at the periphery of the colony as exploratory filaments (Figs. 1A-B, 2 lower left, 3C). Module 2 – sacs: Sacs are series of elongated, club-shaped lateral expansions from the tunnels toward the interior of the substrate and perpendicular to the tunnels and the substrate surface. They contain sporangial swellings of the endolith. Sacs originate from lateral expansions of each cell in the filament, bounded by narrow interconnections at the positions of filament cross walls. Sac formation starts from the colony center and expands toward the periphery (Figs. 1C, 2 upper right, 3B).