Behavioural Aspects of Emergence in the Hydranth of Campanularia flexuosa (Hincks)

Abstract

THE development of the hydranth of Campanularia flexuosa occurs within a capsule of chitin secreted by the hydranth itself^1–4. In order to emerge for the first time the hydranth must in some way dispose of the lid of the capsule. Allman⁴ states that the lid is pushed off in this species. Kramp⁵ observed that, though the lid is removed in Campanularia, it is wholly or partly retained as an operculum in the Campanulinidae. Hammett⁶ assumed that ‘the completely developed hydranth repeatedly surging against the cover with great force’ was responsible for weakening the lid prior to emergence. He suggested that the mechanical properties of the chitin at the junction between lid and cup facilitated the clean disposal of the lid. Enzymatic digestion and localized differences in thickness or quality were proposed as possible factors leading to the separation of the lid, Hauschka⁷ showed that emergence was dependent on the possession of basal attachments to the diaphragm (shelf) and suggested that: “Hydroplasmic pressure adds inflation to the independent exertions of the imprisoned hydranth and may be a contributing factor in emergence”.