Windipila spinifera from the Lower Devonian Rhynie cherts (Windyfield chert). A1, 2. Well preserved specimen in two different focal planes (A1: median optical section, A2: section off center), with prominent spines and otherwise shaped projections extending from mantle (focal plane A1 previously published by Krings and Harper 2018: fig. 1A). Slide SNSB-BSPG 2016 VII 82. B–F. New specimen. Slide SNSB-BSPG 2016 VII 117. B1. Overview (median optical section), showing interior sphere in highly eccentric position and stalk-like hypha (arrow) terminating in exterior sphere. B2. Second exterior structure in different plane; note attached fragment of putative parental hypha (arrow). B3. Shrivelled hyphae or filaments in cavity of reproductive unit. C. Hypha arising from interior sphere (arrows). D. Stalk-like hypha becoming wider in periphery of mantle (arrow), and extending in outward direction. E. Papilla-like, distal putative discharge apparatus of exterior sphere. F. Hypha (rh) with three attached W. spinifera reproductive units (labeled 1–3), of which the one in the lower right of the image (labeled 1) is magnified in Fig. 1B1; specimen 2 occurs on a lateral branch (lb) and 3 at the tip of the hypha. Scale bars: 10 µm (B3, C, E); 20 µm (B2, D); 50 µm (A1, A2, B1); 100 µm (F).