The cocoon-producing cells of Eisenia foetida (Annelida, Oligochaeta): a histochemical and ultrastructural study

Type 1 cells of the clitellar epithelium of Eisenia foetida secrete a protein resembling keratin in histochemical reaction. Ultrastructurally, type 1 cells are characterized by membrane-bound, pockmarked granules ranging in diameter from 1.0 to 3.0 micrometers. Immature granules often exhibit an organized microfibrillar substructure. Individual microfibrils are 17 +/- 1 nm in diameter. Type 2 cell secretion contains protein, nonsulfated acid mucosubstance, and neutral mucosubstance with 1,2-glycol groups. The coarsely fibrillar granules are membrane bound and vary in diameter from 0.5 to 1.0 micrometer. The necks of both type 1 and type 2 cells contain a peripheral ring of microtubules, 20 +/- 1 nm in diameter.