It is also important to understand the life history of gastropods; the larval development strategy (i.e., free-swimming versus direct development) should be known as well as an estimate of when statolith
growth might slow enough during the annual cycle for a growth ring to form.
Stock identification of neon flying squid (Ommastrephes bartramii) in the North Pacific Ocean on the basis of beak and statolith
Arkhipkin and Shcherbich (2012) overviewed various statolith
preparation and processing techniques and suggest how statolith
aging can be improved.
Nearly all of the smallest free-swimming larvae (i.e., 13 of 14), measuring 0.5-1 mm along the oral-aboral axis, lacked bristles by DIC microscopy, yet possessed a dome and four balancers supporting a small statolith
. In slightly larger larvae, 1-2 mm long, bristles were present in a majority of larvae examined (i.e., 6 of 9).
All the squid analyzed in this study were less than 1 year in age, and the results of this study are consistent with the results of previous studies where ages were estimated from statolith
growth increments (Yatsu et al., 1997; Yatsu, 2000).
The age of cephalopods can be estimated by counting accretions in hard structures such as statoliths
, beaks, and-in many decapod squids-gladii.
Age and growth of the naticid gastropod Polinices pulchellus (Risso, 1826) based on length frequency analysis and statolith
growth rings (Gastropoda: Naticidae).
The single large statolith
consists of numerous aggregated living cells, or lithocytes.
Both the funnel organ and statolith
of this species are described based in McGowan & Okutani (1968), Clarke (1978), and Lipinski et al.
However, the neon flying squid grows 0.5-2.7 mm/day in the 18-48 cm ML range (Araya, 1983), and good agreement exists between growth rates obtained from tag-recapture studies and those from statolith
aging studies (Yatsu et al., 1997).
Age estimation was initially evaluated by interpreting growth increments (annular rings) of both the operculum (the corneous plate that closes the opening of the shell when animal is retracted) and the statolith
(calcium carbonate structures within gastropod sense organs used for equilibrium).
A common feature is a fluid-filled cavity that contains a mass (a single statolith
or numerous statoconia) of higher specific weight than the surrounding fluid that can load and mechanically stimulate underlying sensory elements, resulting in behavioral responses to gravity (Horridge, 1969, 1971; Budelmann, 1988).