Presumed photoreceptive cilia in a ctenophore

Four groups of lamellate bodies are symmetrically arranged inter-radially in the floor of the apical organ. Each is composed of many streamed-out membranes of a group of about a dozen cilia, within an invagination of a cell. The rings of ciliary fibrils, of the 9 + 0 pattern, become disarrayed not far from the base. Their dense membranes are lined with granules so that the successive lamellae resemble those of the modified cilia of vertebrate eyes, although flattened in a different plane. On this basis, of ciliary origin, and their resemblance to photoreceptors in fine detail, these structures are interpreted as photoreceptors.