Fasciospongia cavernosa (Schmidt 1862)

Growth form tubular, massive, rounded, usually not larger than 10 cm, sometimes up to 25 cm in diameter. Colour dark brown at the surface, light yellowish at the choanosome. Large and abundant irregular cavities and canals scattered in the mesohyl (etymology of the specific name). Consistency strong and cartilaginous; sponge surface covered by very abundant conules (3–4 mm in height) giving a spiny aspect. External membrane smooth, translucent and resistant; flagellate chambers round (25–30 µm in diameter). Skeleton network very strong with large (50–250 µm) rugose or granulated fibres; some of the largest ones cored by foreign debris can be considered as primary fibres.