INTRASPECIFGICROWTH AND STRUCTURE OF THE SQUID, Illex argentinus (Ommastrephidae) INWINTER AND SPRING IN THE SOUTHWESTERN ATLANTIC. - The intraspecific structureand growth of seasonal cohorts of Illex argentinus were studied on thebasis of statoliths of 900 specimens of Illex argentinus (Ommastrephidae,Teuthida) with mantle length 1.2-39 cm caught in three fishery regions of theExclusive Economic Zone of Argentina (EEZA): on the shelf (depths 130-140 m) and continental slope (depths 400-700 m) in 41-42ºS and 45-47ºS, as well as in the open watersof Argentina Basin between July and October. Squids of all four seasonal groupsat different ontogenetic stages occurred within the regions investigated.Adults of the spring cohort (mantle length 27-37 cm) caught on the slope in 42 and 45-46”S, were characterized by almost maximum growth rates forthe species, being approximately the same as in winter adults hatched inAugust. Two forms were distinguished within summer-hatched squids: a fastgrowing form occurred on the continental slope in 41-42ºS (ML 23-29 cm) and a slow-growing form on the shelf in 45-47ºS (ML 16-19 cm). Juveniles of autumn-hatched squids (ML 8-15 cm) predominated on the shelf in 45-47ºS in September. Growth ratesof juveniles of winter-hatched squids caught on the shelf in 45-47ºS inSeptember-October (shelf form with ML 4-8 cm) were higher than those of winter hatched juveniles in the open waters of the Argentine Basin at the same time (oceanicform with ML 2-4 cm). Possible reasons for growth rate variations of I. argentinus at individual, intra- and intergroup levels are discussed. Anattempt was made to describe probable life cycle variations in each seasonalgroup of squid.