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

[1] It is found in intertidal habitats including tide pools in the vicinity of Auckland, New Zealand.

This is a thickly encrusting sponge with a soft, fleshy texture, growing in patches up to 18 cm across.

The outer layer is bright orange with a yellowish-brown interior.

The surface is marked with widely spaced papillae: When the sponge is in a location affected by wave action, the papillae are located on distinct lamellae running in a single direction over the whole surface of the sponge.