Morphological variability in Illex coindetii (Cephalopoda : Ommastrephidae) along the north-west coast of Africa

This paper gives morphometric variations and dorsal mantle length-total wei ght (DML-TW) relationships for Illex coindetii in the eastern Central Atlan tic area. Positive allometry was observed in males and negative in females of the species. The most variable body measurements between males and femal es were width and perimeter of the head. In the study area, divergence of m orphometric measurement starts at 95 mm. The point of divergence, however, varies with latitude; fluctuating from 104 mm in the north (Morocco and Sah ara) to 76 mm in the central area (Mauritania and north of Senegal) and 73 mm in the south (Gulf of Guinea). The relationships between DML and TW showed that sexual dimorphism due to d ifferential growth between males and females starts to occur at 56 mm ML. T he starting point of sexual dimorphism (56 mm) varies according to the zone ; the higher the latitude, the later it occurs. Thus, sexual dimorphism occ urs at 49 mm in the south (Gulf of Guinea), at 54 mm in the central area (M auritania and north of Senegal) and at 74 mm in the north (Morocco and Saha ra). Females grow larger than males, but males were heavier at any given le ngth. As latitude decreased, a slow down in the increase in weight-at-lengt h was observed in both sexes.