Haplopoma impressum is an encrusting bryozoan. Colonies typically form small patches with a glass-like appearance. Autozooids are hexagonal to oval and often taper proximally. They are 0.5-0.55 by 0.3-0.35 mm.
Haplopoma impressum is distributed southwards from the west of Scotland. It is not known from the north-east. Outside of the UK, the species is known from the Mediterranean.
The species is most commonly found on red algae in shallow water just offshore. It may also colonise Posidonia seagrass.