Fig. 1. Diagram of part of an anemone tentacle in cross section (cells not drawn to scale). The tentacle of Aiptasia pallida is composed of two epithelial layers; ectoderm (epidermis) and endoderm (gastrodermis) separated by a basement membrane termed the mesoglea. The ectodermal layer consists of three regions: a monolayer of longitudinal muscle cells closest to the mesoglea; an intermediate layer of neuritic processes and neurons termed the neural plexus; and the compositionally diverse apical epithelial layer, which includes mucus-secreting cells (MC), multicellular complexes known as cnidocyte/supporting cell complexes (CSCCs) and relatively rare sensory cells. The CSCCs consist of a cnidocyte about 35µm in length surrounded by two or more supporting cells (SC). Three different functional types of CSCC have been identified. Two kinds of cnidocyte occur in the tentacle: the nematocyst-containing nematocyte (CN) and the spirocyst-containing spirocyte (SP). The nematocyte sports a single kinocilium from its apical surface which, in turn, associates closely with a bundle of stereocilia contributed from the adjacent supporting cells of the same CSCC. Together, the kinocilium and stereocilia form vibration-sensitive hair bundles. Sensitizing chemoreceptors for N-acetylated sugars, such as N-acetylneuraminic acid (NANA), occur on the apical surfaces of the supporting cells.