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In biological morphology, a typhlosole is an internal fold of the intestine or intestine inner wall.[1][2] 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.

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  1. ^ Fujii, Tamotsu (July 1982). "Electron microscopy of the leucocytes of the typhlosole in ammocoetes, with special attention to the antibody- producing cells". Journal of Morphology. 173 (1): 87–100. doi:10.1002/jmor.1051730108. ISSN 0362-2525. PMID 7050396. S2CID 37992278.
  2. ^ "Typhlosole - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2023-03-16.

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