Thin (<1 mm), smooth, glossy, red-orange crusts on rock or mollusk substrata. These flat basal crusts give rise to erect protuberances that are short and stubby (typically 2–3 mm diameter and 5–10 mm long), sparsely scattered, and with a strong tendency to become irregularly once or twice bifurcated, as they increase in length. Crusts can be extensive, covering large areas of entire boulders, yet remain sparsely branched. Lithothamnion tophiforme also grows on shells, especially those of scallops. Such crusts on mollusk shells often continue to grow after the mollusk is dead and the shell has become part of loose sediments (Adey et al. 2005).