TISSUE & CELL 1983 15 (6) 939-953 @ 1983 Longman Group Ltd GLEN M. WATSON* and RICHARD N. MARISCAL COMPARATIVE ULTRASTRUCTURE OF CATCH TENTACLES AND FEEDING TENTACLES IN THE SEA ANEMONE HALIPLANELLA Key words: Anthozoa. sea anemone, nematocyst. autophagy. granulocyte. Cnidaria ABSTRACT. TEM observations of catch tentacles revealed that the tentacle tip epidermis is filled with two size classes of mature holotrich nematocysts and a gland cell filled with electron-dense vesicles. Vesicle production is restricted to upper-middle and tentacle tip regions. whereas holotrich development occurs in the lower-middle and tentacle base regions. Thus, catch tentacles have a maturity gradient along their length, with mature tissues concentrated at the tetacle tip. Occasional feeding tentacle cnidae (microbasic p-mastigophores and basitrichs) and mucus gland cells occur in proximal portions of catch tentacles, but are phagocytized by amoeboid granulocytes and transported to the gastrodermis for further degradation. No feeding tentacle cnidae or mucus cells occur distally in catch tentacles. Unlike catch tentacles, feeding tentacles are homogeneous in structure along their length with cnidocytes containing mature spirocysts. microbasic p-mastigophore or basitrich nematocysts distributed along the epithelial surface. Cnidoblasts are recessed beneath cnidocytes. occurring along the nerve plexus. Mucus gland cells and gland cells filled with electron-dense vesicles are present in feeding tentacles. distributed at the epithelial surface. Granular phagocytes arc rare in the feeding tentacle tip. but common in the tentacle base. Introduction sive interactions among non-clonemate sea Two types of tentacle occur in certain sea anemones. One type, the typical feeding tentacle, is a translucent, slender structure that gently tapers from its base to a pointed tip. The second type of anemone tentacle, known as a catch tentacle, is opaque, about twice as wide as a feeding tentacle and blunt-tipped (Williams, 1975). Feeding tentacles function to capture prey. Upon contacting any area of the tentacle, prey items (e.g., small crustaceans) are subdued by nematocyst toxins and held to the tentacle by everted nematocyst and spirocyst threads as the tentacle bends toward the mouth. The prey are subsequently released into the mouth. Catch tentacles are specialized for aggres- anemones. Following contact with a non- clonemate individual, catch tentacles inflate to as much as three or four times their resting length and then touch the upper column or tentacles of the ‘opponent’ using the tentacle tip. Such contact elicits extensive nematocyst discharge, causing the tentacle tip to adhere to the ‘victim’. The tip autotomizes from the catch tentacle as it is withdrawn, and the tip is thus left attached to the victim (Purcell, 1977). In addition to differing in shape and function (above), the two tentacle types differ in the tentacle cnidom (nematocyst complement), with spirocysts dominating feeding tentacles and holotrich nematocyts dominating catch tentacles (Hand, 1955; Williams, 1975; Purcell, 1977). Recently, we found that mature catch tentacle tips zyxwvutsrqponml of-H&- Department of Biological Science, Florida State Uni- versity, Tallahassee, Florida, 32306 U.S.A. planella luciae contained no spirocysts, while * Present address: Department of Biology, University feeding tentacle tips contained no holotrichs of California, Riverside, CA 92125. (Watson and Mariscal, 1983). Received 17 June 1983. It should be clear from the above discus- Revised 27 July 1983. sion that catch tentacles differ from feeding