Statolith microstructure and age of early life stages of planktonic squids Galiteuthis phyllura and Belonella borealis (Oegopsida, Cranchiidae) from the northern North Pacific

Statolith morphology and microstructure were studied in two common species of panktonic cranchiid squids, Belonella borealis [four juveniles with mantle length (ML) 375-450 mm] and Galiteuthis phyllura (13 paralarvae and juveniles, ML 9-235 mm), caught near the bottom and in pelagic layers over the continental slope of Siberia in the northwest Bering Sea. The total number of growth increments within the statoliths ranged from 277 to 294 in B.borealis and from 10 to 209 in G.phyllura. Assuming that these increments were produced daily, both species grow rapidly in length (daily growth rate = 1.13 mm day(-1)) during the first 8-10 months of their juvenile phase in the mesopelagic layers, prior to migration into deeper waters for maturation.