The epithelial luminescent system of Chaetopterus variopedatus

Abstract

The epithelial luminescent gland of the aliform notopods of Chaetopterus variopedatus was investigated by light, fluorescence, and electron microscopy. Among the cell types present, the orthochromatic cells are closely associated with the luminescent zones and, based on fluorescence microscopy, are probably the photoprotein-containing photocytes. The orthochromatic as well as the few mucous cells of the luminescent epithelia are exocrine goblet cells that synthesize, pack and release large amounts of secretory products through an apical pore. Biconcave cells containing peroxisome-like granules and contributing the brush border microvilli of the epithelium are suspected to participate in the light emission process. Supportive cells packed with microfilaments are closely associated with the orthochromatic and mucous cells and probably mediate the extrusion of secretory materials and the ensuing luminescence after stimulation. A few multiciliated cells are also present.A subepidermal plexus underlies the luminescent epithelium and includes a large number of peripheral nerves and neurites ensheathed by large gliointerstitial cells and processes. Direct neuroeffector cell contacts are absent except for a few close appositions between neurites and supportive cells. The structural organization of the epithelium and of the nerve plexus is discussed in relation to possible neural and cellular control mechanisms in bioluminescence.