Sponges are radially symmetrical metazoans which belong to the phylum Porifera. They are sedentary,a fairly rigid, perforated bag, whose inner surface is lined with flagellated cells called choanocytes. On the outside surface they are lined with spicules.These spicules maybe calcareous or siliceous spicules, or they maybe fibbers composed of a collagenous protein called spongin. The spicules mainly provide support to the to the organism and also protect from predators. The spicules of the sponge visible in this video are a monoaxon spicule having only one axis.