GROWTH OBSERVATIONS ON OCTOPUS VULGARIS CUVIER, 1797 FROM THE PORTUGUESE WATERS: GROWTH LINES IN THE VESTIGIAL SHELL AS POSSIBLE TOOLS FOR AGE DETERMINATION

摘要

Ageing in cephalopods is critical to understanding the life cycle and the dynamics of the species, making it crucial to develop adequate techniques. In the case of octopus species, few studies have been produced in this field, although ageing based on statoliths is quite developed for several species of squids. Young (1960) related the existence of concentric rings in statoliths of Octopus vulgaris, but no description about its deposition form was made. Lipinski (1978) used statoliths to determine the age of ommastrephid squid which, presently, is one of the most widely used methods for ageing in cephalopods (except the octopus). Arkhipkin and Bizikov (1991) made a comparative study of the determination of age using statoliths and gladius of squids. Gongalves (1993) mentioned the presence of concentric rings in the vestigial shell and in the crystal-clear of O. vulgaris and Raya and Hernandez-Gonzalez (1998) described a regular pattern of micro-increments in beaks of 0. vulgaris that maybe indicate a constant temporal basis; Leal (1982, 1984) and Cabido (1984) have also studied the biometrics of vestigial shell of Eledone cirrhosa and O. vulgaris. This structure was referred by Wells (1978) as a reduced shell restricted to two very fine and long structures inserted in mantle muscle on the gill base. This vestigial shell is possibly comprised of an organic matrix with calcium carbonate like the other mollusc shells.