Statoliths as 'black boxes' (life recorders) in squid

The present study presents an overview of recent developments in statoliths studies. Statoliths are calcareous structures located in the equilibrium organs of cephalopods, which serve to detect body accelerations during movement in water. They are perfect 'black boxes' because they record a lot of information about the lives of squid and cuttlefish. For instance, it is possible to reveal the hatchling size and temperature of embryonic development, estimate age and growth rates of the animal with daily precision, date life transitions, analyse possible migratory routes and population structure of squid using trace element analysis, and even reveal how many spawning events a given animal has had by analysing statolith microstructure. Furthermore, because the paralarval statolith is embedded completely within the adult statolith, its features can be used to identify cephalopod paralarvae, which are sometimes very different from adult animals. The shape of statoliths is physiologically specific, which enables the determination of the movement pattern of the animal. Statoliths are usually one of the few remains of squid in fossil records, and their features can be used to infer ideas about the life styles of extinct species.