Olive Chiton

• The teeth of its radula are coated in magnetite, an iron mineral that makes them one of the hardest biological structures known and lets them scrape the rock.
• It has light-sensitive organs distributed across the plates of the shell themselves.
• Its shell is not one piece: it is eight articulated, overlapping calcareous plates joined by a muscular girdle. That structure lets it bend and mould itself to irregular surfaces without losing its grip, and roll into a ball if it is dislodged.
• It has eyes in its shell. Chitons possess aesthetes, sensory organs that pass through the plates, and in some species these include complete eyes with aragonite lenses — that is, lenses made of mineral. It is the only known case of eyes with calcium-carbonate lenses.
• The teeth of its radula are reinforced with magnetite, an iron mineral, which makes them the hardest teeth known alongside those of the limpet. With them it rasps the rock directly.
• It returns to its spot like the limpets: it goes out to graze at night and comes back to the same position on the rock.
• Chitons are an ancient, conservative lineage, with fossils from the Cambrian, and their anatomy is considered close to that of the earliest molluscs.

Skeleton type

Invertebrate - shell of eight calcareous plates (mollusc)

Habitat & environment

Intertidal and shallow subtidal rocks of the Mediterranean

Sources consulted: Speiser, Eernisse y Johnsen (2011), Current Biology, sobre los ojos de aragonito; Marine Life Information Network; Fauna Ibérica