Radula. Specimen from Orkney. February 2015. Leg. P. Lightfoot per J. Porter.
1: dorsal view of teeth through translucent radula sac.
2: ventral of chitinous ribbon.
3: edge view.
As on chitons generally, the radula is a chitinous ribbon bearing teeth in rows of seventeen.
The teeth are colourless when their formation commences at the rear of the translucent radula sac (4). They darken and harden through rust-red and brown(5) as they move along the sac acquiring magnetite (iron oxide), and the principal cutting teeth are black by the time they emerge from the anterior of the sac (6). Magnetite is the hardest material made by any living organism (Botelho, 2013).
T. marmorea feeds by scraping microalgae and associated organisms from the rock surface with its radula.

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