Growth, age and somatic production of the benthic predator Odontocymbiola magellanica were studied in Golfo Nuevo (42S 65W), on the South American Atlantic shelf. Stable oxygen isotope ratios confirmed semiannual formation of internal and external shell growth marks. Mean shell length (SL) of females was 115 and 112 mm for males, while population modal shell-free wet mass (SFWM) was 62.8 g. A Gompertz growth function (SL¥ = 200 mm, K = 0.197, t0 = 5.486) fitted 113 pairs of size-at-age data (12 shells) best. O. magellanica is a long-lived species, reaching up to 20 years of age. The maximum individual somatic production of 29.3 g SFWM per year is attained at 145 mm SL, which corresponds to about 12 years of age. The life span of this volutid seems to be twice compared with other large gastropods. O. magellanica is a valuable and exploitable resource regarding its large size and somatic production, but on the other hand, its slow growth, late maturity and direct development makes it extremely vulnerable to overexploitation.Growth, age and somatic production of the benthic predator Odontocymbiola magellanica were studied in Golfo Nuevo (42S 65W), on the South American Atlantic shelf. Stable oxygen isotope ratios confirmed semiannual formation of internal and external shell growth marks. Mean shell length (SL) of females was 115 and 112 mm for males, while population modal shell-free wet mass (SFWM) was 62.8 g. A Gompertz growth function (SL¥ = 200 mm, K = 0.197, t0 = 5.486) fitted 113 pairs of size-at-age data (12 shells) best. O. magellanica is a long-lived species, reaching up to 20 years of age. The maximum individual somatic production of 29.3 g SFWM per year is attained at 145 mm SL, which corresponds to about 12 years of age. The life span of this volutid seems to be twice compared with other large gastropods. O. magellanica is a valuable and exploitable resource regarding its large size and somatic production, but on the other hand, its slow growth, late maturity and direct development makes it extremely vulnerable to overexploitation. Fil: Bigatti, Gregorio. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biología. Laboratorio de Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina Fil: Penchaszadeh, Pablo Enrique. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biología. Laboratorio de Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina Fil: Cledón, Maximiliano. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Marinas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina