Note:  Do not rely on this information. It is very old.

Horny Sponges

Horny Sponges, or Keratosa, the division of sponges including the common sponges of commerce. They belong to the division Noncalcarea, from which-they differ in the absence of spicules and the presence of numerous fibres of "spongin" or "keratose" which compose the sponge. [Sponge.]