- A convoluted invagination of the cytoplasmic membrane in some bacterial cells.
- A folded invagination into the plasma membrane of bacteria, from the substance fixation methods accustomed prepare samples for electron microscopy, but previously considered to be part of the typical construction associated with the cell.
- In crustaceans, the pereion or thorax. Compare metasome and urosome.
- just like mesosoma.