Diadema paucispinum is a small sea urchin with very long, moveable spines which are slender and sharply pointed.

[2] There are photosensitive spots in the urchin's epidermis and if a shadow falls on the animal, it angles its secondary spines towards the intruder.

[2] Near the apex of the test is a clearly visible anus surrounded by an orange ring and raised on a small projection.

One was originally considered to be limited to Hawaii but has now been found on Easter Island, Pitcairn, and Okinawa.

[2] Diadema paucispinum is nocturnal and grazes on filamentous algae as it crawls over the rocks.