With 3 plates and 5 figures in the text)Morphology and microstructure of the gladius and statolith were studied from 11 specimens of the boreal Pacific giant squid Moroteuikis robusio (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 . rohustu 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 . rohusta. 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 . robusfa gladius grow synchronously. M . robusfa statoliths are tiny (0.07 -0.1 ML) and resemble in shape those of the ommastrephid Illex urgentinw. 11 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 . rohustci 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. 475 7' 1997 The Zoological Society of London 476 V . A . B I Z I K O V A N D A. I. ARKHIPKIN
Materials and methodsEleven specimens of M. robusta (all of them were females of the second stage of maturity) were caught within the Exclusive Economic Zone of Russia in the Bering Sea during a research trawl-survey on the gonate schoolmaster squid Berryteuthis rnagister carried out in summer and autumn 1993. Hauls were made by the fishery mid-water trawl with vertical opening 8 m, horizontal opening 84 m and mesh size 45 mm. All the trawls were made near the bottom at depths ranging from 350 to 460m with durations of 3-6 h at an average speed of 4.0 knots. From the total of 350 trawls, M. robusta were found only in 10. Dorsal mantle length (ML), sex, weight, stomach content, and some morphometrics were assigned for each specimen (Table I).The statoliths and gladii were extracted from each specimen for further morphological and growth analyses on board the ship. The gladii were sampled, stored and processed according to an improved technique developed by the first author (Bizikov, 1990(Bizikov, , 1991. Cross-sections of each gladius were made at 2 levels: at the cone apex and at the greatest thickness of the proostracum. Morphological description, processing, and counting of statoliths were performed after Arkhipkin (1 991).
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