Otolith

Otolith
Otolith organs showing detail of utricle, otoconia, endolymph, cupula, macula, hair cell filaments, and saccular nerve
Juvenile herring. Length 30 mm; 3 months old; still transparent; the otoliths are visible left of the eye.
Details
Identifiers
Latin	statoconium
MeSH	A09.246.631.909.625.125.680
TA	A15.3.03.086
FMA	77826
Anatomical terminology []

An otolith (οτο-, oto-, ear + λιθος, lithos, a stone), also called statoconium or otoconium or statolith, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. They have been identified in both extinct and extant vertebrates. Counting the annual growth rings on the otoliths is a common technique in estimating the age of fish. The saccule and utricle, in turn, together make the otolith organs.

Endolymphatic infillings such as otoliths are structures in the saccule and utricle of the inner ear, specifically in the vestibular labyrinth of all vertebrates (fish, amphibians, reptiles, mammals and birds). In vertebrates, the saccule and utricle together make the otolith organs. Both statoconia and otoliths are used as gravity, balance, movement, and directional indicators in all vertebrates and have a secondary function in sound detection in higher aquatic and terrestrial vertebrates. They are sensitive to gravity and linear acceleration. Because of their orientation in the head, the utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator).

Similar balance receptors called can be found in many invertebrate groups but are not contained in the structure of an inner ear. Mollusk statocysts are of a similar morphology to the displacement-sensitive organs of vertebrates; however, the function of the mollusk is restricted to gravity detection and possibly some detection of angular momentum. These are analogous structures, with similar form and function but not descended from a common structure.