A substance released by metamorphosing larvae and young polyps ofHydractinia echinata induces metamorphosis in conspecific larvae.

A metamorphosis-inducing factor was isolated from medium conditioned by either metamorphosing larvae or 3-day postmetamorphic primary polyps. The factor has a molecular weight ≥ 8 kDa and is heatlabile. It does not induce metamorphosis of isolated posterior fragments and is therefore not identical to the internal signal described by Schwoerer-Böhning et al. (1990). The biological significance of the substance is currently unclear, therefore its inducing activity may be a side effect.