The blue ray limpet, Patella pellucida, is named after the striking iridescent blue lines that radiate on the top of the shell. This shimmering, seemingly ephemeral colour is due to diffraction of light by the reflection grating structure of the P. pellucida shell (Shigley and Hurwit, 1999 Optics Express 4 pp. 177-182). This diffraction is common to all molluscan shells but is dependent on the groove density and the surface quality of the shell and is therefore not always visible.
The Blue Ray Limpet, Patella pellucida
P. pellucida is a herbivorous, grazing on Laminaria spp. in the low tide zone. The larvae graze firstly on encrusting corraline algae, later migrating to Laminaria (Kitching, 1987 Advances in Ecological Research 17 pp. 115-186). It is known from the fossil record from the Pliocene era to Recent (Marques da Silva et al., 2006 Palaeogeography, Palaeoclimatology, Palaeoecology 233 pp. 225– 234).