STATOLITH SHAPE AND MICROSTRUCTURE IN STUDIES OF SYSTEMATICS, AGE ANDGROWTH IN PLANKTONIC PARALARVAE OF GONATID SQUIDS (CEPHALOPODA, OEGOPSIDA) FROM THE WESTERN BERING SEA

The microstructure, morphology and ontogenetic development of statolit hs and age and growth of 405 planktonic paralarvae and 117 juveniles b elonging to 10 species of gonatid squids (Cephalopoda, Oegopsida) were studied in the region of the continental slope in the western part of the Bering Sea (57 degrees 00'-61 degrees 30'N, 163 degrees 00'E-179 degrees 20'W). The statolith microstructure of all species was charact erized by the presence of a large droplet-shaped nucleus and bipartite postnuclear zone divided into two by the first stress check, except f or Berryteuthis magister which had only one stress check and an undivi ded postnuclear zone. In Gonatus spp., completion of development of th e postnuclear zone coincided with full development of the central hook on the tentacular club. Daily periodicity of statolith growth increme nts was validated by maintaining 13 paralarvae of the four most abunda nt species in captivity. All species might be subdivided into two grou ps based on statolith microstructure, i.e. species with a central posi tion of the nucleus within the first statolith check (Gonatopsis spp., Egonatus tinro and B.magister) and species with the nucleus shifted t o the inner side of the first statolith check (Gonatus spp.). Comparat ive analysis of statolith morphology showed that paralarval statoliths have species-specific characters that allowed the construction of key s to identify species of gonatid paralarvae based on their statoliths. Analysis of paralarval growth using statoliths revealed that these co ld-water planktonic gonatid paralarvae have fast growth rates, attaini ng a mantle length of 7-10 mm at 15-20 days and 20-25 mm at 35-70 days .