The cuticulosome is a spherical, iron-rich structure located in the
cuticular plate
The reticular membrane (RM, also called reticular lamina or apical cuticular plate)hair cells in birds. Cuticulosomes are 300-600 nm in diameter and are composed of
ferritin
Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. It is the primary ' ...
-like granules that in some cases are structured in paracrystalline arrays. Due to its specific location in sensory hair cells of the inner ear and its iron-rich composition it was proposed to be involved in the
magnetic sense
Magnetoreception is a sense which allows an organism to detect the Earth's magnetic field. Animals with this sense include some arthropods, molluscs, and vertebrates (fish, amphibians, reptiles, birds, and mammals, though not humans). The se ...
of birds. However, physical simulations and calculations showed that it lacks sufficient
magnetic susceptibility
In electromagnetism, the magnetic susceptibility (Latin: , "receptive"; denoted ) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the ap ...
to act as a torque based magnetoreceptor. An alternative hypothesis suggests that the cuticulosome might work as an intracellular electromagnetic oscillator to detect magnetic fields.