An almost round body with a strong shell. The spines are few but very well developed. the base of each spine is surrounded by tube feet and small pincer-like organs called "pedicellariae". The body is pinkish and the spines are grey with more or less visible brownish streaks. The shell is a yellowish white.
Sexual maturity is apparently reached in the second year. Specimens with eggs have been seen between May and June. Pencil urchins feed mainly on algae lawns and smaller invertebrates like sea squirts or sponges. The spines are often encrusted with numerous other organisms.