mesothelium
The layer of flat cells, derived from the mesoderm, that line the coelom or body cavity of the embryo. In the adult, it forms the simple squamous epithelium that covers all true serous membranes (peritoneum, pericardium, pleura).
peritoneum
serous membrane that forms the lining of the abdominal cavity or the coelom—it covers most of the intra-abdominal (or coelomic) organs—in amniotes and some invertebrates
serous membrane
smooth coating of body cavities (thorax and abdomen), smooth, shiny, translucent and content with a thin layer of liquid