Morphology and microstructure of the gladius and statolith from the boreal Pacific giant squid Moroteuthis robusta (Oegopsida; Onychoteuthidae)

Morphology and microstructure of the gladius and statolith were studied from 11 specimens of the boreal Pacific giant squid Moroteuthis robusta (mantle length (ML) ranging from 97.5 to 141.5cm) captured on the slope of the north‐west Bering Sea in summer and autumn 1993. The most specific feature of the M. robusta gladius is a large and, in cross‐section, round rostrum which has been found to be homologous to that of extinct Belemnitida. The functional morphology of the different gladius elements is discussed. Distinct growth increments have been revealed in all three gladius layers in M. robusta. Comparison of peculiarities of microstructure of growth increments, their ways of deposition and their numbers in different gladius layers has shown that all three layers in the M. robusta gladius grow synchronously. M. robusta statoliths are tiny (0.07‐0.1% ML) and resemble in shape those of the ommastrephid Illex argentinus. It was impossible to count the total number of growth increments within the statoliths, owing to their complete disappearance in the outer portion of the peripheral zone, and therefore impossible to estimate the age of the M. robusta by using the statolith ageing technique. However, assuming the deposition of growth increments within the gladius as daily, the age of the specimens analysed may vary from 413 to 520 days.