Haplopoma planum is an encrusting bryozoan that forms small patch-like colonies. Autozooids are oval to rhomboidal and larger than the autozooids of other Haplopoma species.
Haplopoma planum ranges from Shetland and western Norway to the Arctic.
The species is able to colonise stones, shells and the cold-water coral Lophelia. It occurs in subtidal waters at depths greater than 50 m.