Black Leather Sponge

Growth form regular, massive, rarely exceeding 10 cm in diameter. Colour black or dark grey in vivo. Consistency strong, relatively elastic. Surface finely conulose (1–2 mm in height and 2–3 mm apart). Oscules (up to 1 cm in diameter) irregularly scattered. Skeleton network reticulation of ascending primary fibres (90–180 µm in diameter) with a fibrous narrow core free of inclusions or bearing only rare spicules. Secondary fibres (50–100 µm in diameter) uncored and laminated. Filaments (0.7–2.0 µm in diameter) very abundant giving a strong consistency.