THE DEVELOPMENT OF A SEA ANEMONE TENTACLE SPECIALIZED FOR AGGRESSION: MORPHOGENESIS AND REGRESSION OF THE CATCH TENTACLE OF HALIPLANELLA

Three intermediate catch tentacle morphs were observed in the sea anemone Haliplanella luciae during catch tentacle development. Stage 1 catch tentacles, characterized by swollen bulb-like regions along their length, were histologically similar to feeding tentacles. Stage 2 catch tentacles, which tapered normally along most of their length and then constricted near the tip, were characterized by the presence of feeding tentacle cnidae in the tentacle coelenteron as they were removed from developing catch tentacles. Numerous cnidoblasts appeared in stage 2 tentacles and then synchronously matured into small holotrich nematocysts, a cnida characteristic of mature catch tentacles. Stage 3 catch tentacles were characterized by the appearance of many large holotrich nematocysts. Such tentacles appeared similar to mature catch tentacles with wide, opaque, blunt tips. However, stage 3 catch tentacles had fewer large holotrichs per total tentacle cross section than mature catch tentacles. The numbers of large and small holotrich nematocysts decreased in regressing catch tentacles, which tapered to opaque, pointed tips. However, these cnidae did not move to the coelenteron as before but instead migrated to the epithelial surface. This migration suggested that they were externally expelled from the tentacles.