Description: Small thin encrusting disc about 2 mm in diameter, margin thin with smooth surface. Conceptacles forming domed and raised chambers.

Habitat: Rare. Epiphytic usually Zostera, sublittoral to 3 m.

Distribution: Recorded from a few sites in the British Isles: Dorset, south Wales, Ayrshire and in Ireland. Europe: Mediterranean and Sweden. Further afield: Canary Isles, the Arabian Gulf, Australia. Probably under-recorded.

Distribution Map from NBN: Hydrolithon cruciatum at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Hydrolithon cruciatum at iNaturalist World Species Observations database.

WoRMS: Hydrolithon cruciatum at World Register of Marine Species.