Poromya granulata is a dull-white coloured shell with dome-shaped valves and grows to about 18 millimetres (0.71 in) long.

The surfaces of the valves have faint concentric sculpture lines and are covered in rows of fine granulations.

The inside of the valves is nacreous and the pallial line has a broad, shallow sinus.

[3] Poromya granulata has a subarctic and boreal distribution on either side of the North Atlantic Ocean.

The fringe of tentacles round the siphons have sensory cilia which are believed to alert the animal to the presence of moving prey in the vicinity.