Observations concerning the metabolism of iodine by polyps of Aurelia aurita

In the Scyphozoan jellyfish, Aurelia aurita, iodine is necessary for, and capable of initiating, the process of strobilation, by which the sessile polyp is transformed into the free-swimming medusa. Iodine metabolism in polyps of Aurelia aurita was studied, therefore, with a view to elucidating its role in the initiation of strobilation. Polyps were incubated under varying conditions in artificial seawater containing inorganic 125I. It was found that organification is the major means by which polyps accumulate iodine. Accumulation of 125I was greatly inhibited by methimazole, but not by perchlorate, and directly measured polyp/medium iodide concentration gradients were low (< 3:1). Chromatographically immobile and only partially hydrolyzable “origin material” was the major product of iodine metabolism. Both MIT and DIT were formed and released into the incubation medium, with DIT in predominance. Another iodocompound that was chromatographically distinct from 3,5-T 2, T 3 and T 4 was also detected, but remains unidentified. No trace of 125I-labeled T 4 was ever detected, even under conditions in which strobilation was induced. Coupled with evidence from previous studies, the findings suggest that T 4 is not the agent responsible for initiation of strobilation in Aurelia.