Polymastia lorum is a species of sea sponge belonging to the family Polymastiidae.

It is only known from a single specimen found attached to a dead Glycimeris valve on a reef near Ohinau Island, one of the Mercury Islands off North Island, New Zealand.

This is a small encrusting sponge 4 cm across.

The outer layer is yellow with an orange-red interior.

The most remarkable feature of this sponge is its incredibly long (up to 6 cm) strap-like papillae.