Stage 2 intermediate catch tentacle
Feeding tentacle cnidae (spirocysts, microbasic p-mastigophores, and basitrichs) migrate (or are phagocytized by granulocytes and then transported) from the epi thelium to the coelenteron in stage 2 tentacles. Hence, feeding tentacle cnidae are gradually removed from developing catch tentacles, but their fate beyond this point is not known. Perhaps these so-called “¿ gastrodermalcnidae―are inserted into other anemone tissues (e.g., into other feeding tentacles) or somehow eliminated and/or expelled from the anemone. The “¿ removal― of feeding tentacle cnidae is followed by the appearance of numerous cnidoblasts in the epithelium. It is possible that interstitial cells (stem cells) migrate into stage 2 tentacles and then differentiate into cnidoblasts or, alternatively, that local stem cells (already present) proliferate and then differentiate into cnidoblasts. Since stage 2 tentacles were filled with numerous small holotrich cnidoblasts, or with numerous small holotrich cnidocytes, and not a mixture ofthe two, it is clear that the cnidoblasts synchronously mature into catch tentacle cnidocytes (the mature cell containing the mature structures).
Stage 3 intermediate catch tentacle
Large holotrichs are usually absent from the tips of stage 2 intermediate catch tentacles (which can contain numerous small holotrichs), and first appear in the tips of stage 3 intermediate catch tentacles. However, stage 3 catch tentacles consistently have fewer large holotrichs in their epithelia than mature catch tentacles (although stage 3 catch tentacles have about as many small holotrichs as mature catch ten tacles). Thus, the appearance of large holotrichs occurs much later during catch tentacle development than the appearance of small holotrichs. These data suggest that the differentiation of interstitial cells into large holotrich cnidocytes is regulated so that the interstitial cells do not form into large holotrich cnidocytes until after many small holotrich cnidocytes have been produced and line the epithelial surface (i.e., late in catch tentacle development). Since stage 3 catch tentacles lack cnidoblasts at the tentacle tip, the source of the additional cnidae that are necessary for final catch tentacle maturation is un known. Perhaps the pulse-like appearance of cnidoblasts and synchronous matu ration into holotrich cnidocytes (observed in stage 2 tentacles) recurs throughout catch tentacle development. On the other hand, holotrichs might be produced in proximal tentacle regions and then transported through the tentacle coelenteron to be inserted into the distal tentacle epithelia. Another possible explanation is based on the fact that stage 3 catch tentacles, like mature catch tentacles, are functional, aggressive structures that autotomize their tentacle tips during normal functioning. Thus, this “¿ deficiency― in the number of cnidae per tentacle section might be over come by tissue renewal processes in the “¿ new― catch tentacle tips following tentacle tip autotomy during aggression.