Statolith microstructure was studied in hatchlings of deepwater-spawned gonatid squid Gonatus onyx, caught between 1350 and 1420 m over a bottom depth of 2100 m in the San Clemente Basin off San Diego, California. It was found that the shape and size of the hatchling statolith were similar to those of the first-check statolith observed in paralarvae and small juveniles of G.onyx. The inner part of the bipartite postnuclear zone (= first-check statolith) is formed during late embryo-genesis, and the first check within the statolith microstructure must be considered as a starting point of increment counting for age estimation of Gonatus spp.