Fine structure of the mucous cell in the sea pen, Ptilosarcus guerneyi, with special emphasis on the possible role of microfilaments in the control of mucus release

Abstract

One unique feature of the ectodermal mucous cell in the sea pen, Ptilosarcus guerneyi, is the possession of an apical sac, which is formed by the infolding of the apical cell membrane. The apical sac is guarded by several rows of microvilli at the rim of the opening and is surrounded intracellularly by arrays of microfilaments. The microfilaments, 50 Å in diameter, are interrupted by treatment with cytochalasin B (10–20 μg/ml) for 4 h. We provided morphological evidence to suggest that the apical sac is used for mucus storage and that contraction of the microfilaments would release the mucus from the sac.Other features of significance, such as the possible relationships between calcium transport and apical vesicles and between mucus release and bioluminescence are also reported.