Saccomorpha velum Hook, Radtke, Campbel et Golubic, 2024

Key feature (diagnosis): S. velum consists of euendolithic traces with flat-based, sail-shaped intercalary, and arrowheadshaped terminal sporangial swellings, interconnected by straight hyphae-containing tunnels, 1.5 to 2.5 μm in diameter (slightly wider than those interconnecting sporangial swellings in S. clava), extending straight for long distances. Intercalary sporangial swellings form along these tunnels 40 to 150 μm apart. The trace network usually starts from a central distribution centre composed of one to several sporangial swellings in a group (Figs. 5a, b) connected with the substrate surface by a slightly inclined neck. Less frequently, the network originates by spores germinating inside sporangia, producing several hyphal tunnels exiting in all directions from a single central isodiametric swelling, described below as a separate morphotype S. radiata (Fig. 5c). The intercalary swellings are elongated, ca. 10 μm wide, up to 18 μm long and 10 to 12 μm tall (deep) adhering directly to the hyphal tunnels (without a neck) usually in the form of a flat upright sail (Fig. 5d). The terminal swellings have a distinctive arrowhead outline (Fig. 5a, b, and e, lower left).