What is "typhlosole"

Typhlosole \Typh"lo*sole\, n. [Gr. ? blind + ? channel.] (Zo["o]l.) A fold of the wall which projects into the cavity of the intestine in bivalve mollusks, certain annelids, starfishes, and some other animals.

n. a fold in the surface of the intestines of some invertebrates etc that increases its digestive surface area

A typhlosole is an internal fold of the intestine or intestine inner wall. Typhlosoles occur in bivalve mollusks, lampreys and some annelids and echinoderms.

In earthworms, it is a dorsal flap of the intestine that runs along most of its length, effectively forming a tube within a tube, and increasing the absorption area by that of its inner surface. Its function is to increase intestine surface area for more efficient absorption of digested nutrients. In different earthworm families, the typhlosole appears to have multiple origins. The Lumbricidae, for example, have a typhlosole which is an infolding of all layers of the intestine wall, whereas in some other families (e.g. Megascolecidae), it is an infolding of only the inner layer, and in many earthworms it is absent.