The ultrastructure of epidermal mucous cells in marine invertebrates (Nemertini, Polychaeta, Prosobranchia, Opisthobranchia).

The epidermal mucous cells of various nemerteans, polychaetes and gastropods exhibit a highly heterogeneous fine structure, which is not correlated to systematic position or way of living. Formation and extrusion of the mucus secretory substances also follow different patterns. In the majority of species investigated, the mucus inclusions originate in the Golgi area, in Pomatias they form in the rough endoplasmic reticulum. The mucus droplets either coalesce in the cytoplasm or retain their individuality before being extruded. [ABSTRACT FROM AUTHOR]