typhlosole

A longitudinal fold of the intestinal wall in certain invertebrates that increases the absorptive and digestive surface area of the intestine.

A thick folding of the intestine of certain annelids, mollusks, etc, formed by the involution of the wall of the intestine along the dorsomedian line, and projecting into the intestinal cavity.

A fold of the wall which projects into the cavity of the intestine in bivalve mollusks, certain annelids, starfishes, and some other animals.

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