Fig. 1 Shell length, age and ventilatory behaviour in Lymnaea. (A) The growth of snails (as measured by shell length) was linear between 3.5–13 weeks of age (post-hatching). Snails were maintained in standard conditions and a cohort (N=33) of randomly selected snails from the over 200 snails in the aquarium were measured weekly. The snails displayed continuous shell growth at a rate of 0.25 mm day^–1. Based on this growth curve adults (2.5 cm) and juveniles (1.5 cm) are approximately 13 and 8 weeks old, respectively. (B) Increased aerial respiration in hypoxia. Both adult (N=43 each) and juvenile snails significantly (P<0.01 in both cases) increase their total breathing time when exposed to the hypoxic environment. However in both eumoxia and hypoxia the total breathing time in adults was significantly greater (P<0.001) than in juveniles.