Settling of the larvae ofSiboglinum fiordicumWEBB (Pogonophora) in the laboratory

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Abstract
The paper presents the results of a series of settling experiments with larvae of S. fiordicum. It also gives some notes on the behaviour of larvae and adult during incubation. Three larval stages are described of which two are reached during incubation, the third soon after settling. The larvae normally had a free-swimming period of less than two hours after discharge. The most advanced larvae did not swim and burrowed immediately. The initial burrowing was accomplished with the anterior end first, chiefly by means of the body musculature and the anterior ciliary ring. Within two to five days after discharge the larvae underwent a slight metamorphosis just below the sediment surface and then burrowed backwards down to about 10 cm depth using the posterior segment. Experiments on settling without sediment and forced extension of incubation showed that the larvae were stimulated to settle by the release from the parental tube, and that the presence of sediment acts as an additional stimulus. Discharged larvae were able to postpone settling for about three days during unfavourable conditions.