Red Encrusting Sponge

This species displays a variety of different habits: It forms thin encrustations with several root-like canals from the slightly raised oscules (M. arbuscula-oscula). These canals often intertwine and connect with canals radiating from other oscules. But the species can also form erect, lobate branching, bushes, with highly penicillate surface projections. Up to 12 cm high and wide. The projections are 5-10 mm long, irregular in outline and spiny.
Color: Both growth forms are brilliant red. Especially in encrusting forms, the white spots between the canals are conspicuous, forming lighter areas.

Remarks:
The erect form resembles Ptilocaulis walpersi .