Description

 Polymastia boletiformis is a firm sponge that exhibits either a cushion or massive form and grows up to 10 cm in diameter. The surface is smooth and bears numerous papillae. The papillae are stout, cylindrical and flexible and taper sharply towards the tip. Each papillae bears a visible exhalant oscula on the upper surface and can be 2-12 cm long. The whole of the sponge is orange, ochre-yellow, dark grey or green in colour. The body walls are supported by siliceous spicules.This species has benthic larvae that are motile for 18-20 days before settling for up to 7 days, after which they metamorphose into the adult form. Polymastia boletiformis is similar to Polymastia mammillaris but the latter has a rough surface, and papillae that are paler in colour than the base and do not taper as sharply as those in Polymastia boletiformis.