The sheets of peritoneal membrane that hold the digestive tract in place are called the sheets of peritoneal membrane that hold the digestive tract in place are called serosal lining lamina propria mesenteries mucosal lining

They are called the mesenteries. They are also called the mesenterium, they are peritoneal fold attaching to the small intestine to the dorsal body wall.In humans it wraps around the pancreas and the small intestine and extensions down around the colon and the upper portion of the rectum. Their function is to anchor the small intestine to the walls of the abdominal walls.

They formed the oceans.  as they melted water was formed and the water made the oceans