Like other sea urchins, the rough pencil urchin belongs to the phylum Echinodermata.
All sea urchins are covered with spines (hence their name: ‘Echino’ means spiny and ‘derm’ means skin) which move on ball and socket joints. They use the spines to defend themselves against predators.
Pencil urchins have large heavy spines which are often sold as ornaments. The spines are initially purple but they usually get covered with algae so the colour is hidden except at the base.
Spines are initially purple