AbstractAnnual internal growth banding ofArctica islandicahas shown that the species has a surprising longevity of up to 149 years as stated byTHOMPSON,JONESandDREIBELBIS(1980). The authors have compiled 100 values of valve height against age as reproduced in Figure 1. Visually gained growth curves have been added for single specimens that leave some doubt as to the existence of an inflexion point. In this paper a cross‐sectional evaluation of growth behaviour is carried out with nine funtions using nonlinear regressions. Five growth functions yield almost equally good results with a final valve height just below 100 mm. An inflexion point is either present in early youth or lacking altogether, depending on the growth function use