The species is characterised by its minute, black, sunken reproductive structures (perithecia) that measure 0.10–0.24 mm in diameter and create small pits in the substrate.

The species can be distinguished from similar marine lichens by its consistently small, deeply embedded perithecia and its ability to maintain stable growth by keeping pace with natural substrate erosion.

The type specimen was collected by Edward Morell Holmes from shells washed up on the shore at Robin Hood's Bay, North Yorkshire.

Each perithecium is covered by a black, protective cap (involucrellum) that appears "lid-like" and lies either flat or slightly convex against the surface, with minimal lateral spread.

[4] Collemopsidium foveolatum can be distinguished from similar species, particularly C. sublitorale, by its consistently smaller perithecia that remain deeply embedded in the substrate rather than protruding.

[4] Research has confirmed the distinctive zonation patterns of marine lichens like C. foveolatum in the eulittoral zone, demonstrating that these species possess specific traits adapted to regular seawater immersion, including higher proportions of cyanobacterial photobionts and perithecioid fruiting bodies.