The typhlosole in earthworms increases the surface area of the intestine for efficient secretion and absorption during digestion. It is named for the Greek word for "blind pipe," and the typhlosole can be defined as an extra flap of tissue or an infolding along the inner wall of the intestine. However, the typhlosole varies according to the family of earthworm.
For various families of earthworms, the typhlosole seems to have more than one origin. Some families have a typhlosole that is an infolding of all layers of the intestinal wall, but other families may not have a typhlosole at all. Typhlosoles are found in members of the annelids phylum and even some bivalve molluscs. In earthworms, the typhlosole is normally a yellow or orange color and is located on the top, or dorsal, part of the worm's inner intestinal wall. To view a typhlosole, you must dissect the earthworm and cut open the intestine. According to cross-section diagrams of earthworms, the typhlosole is surrounded by the intestinal lumen. The outside of the intestine and a majority of the inside of the typhlosole is a specialized tissue composed of chloragogue cells, and these cells perform metabolic functions including creating fats and hemoglobin.