The intestine is one of the most "popular" places for parasites to live, but presents many challenges to parasites. There are strong peristaltic forces throughout much of the intestine, and the abrasive action of intestinal contents that can dislodge parasite that are not anchored securely. The internal surface of the intestine is soft, and its epithelium is turning over constantly. Parasites need to anchor deeply, or be able to re-attach constantly. The surface topography also changes from one region of intestine to another, so attachment organs that work well in one location may be less effective in another.
Hookworms embed their anterior ends in the intestinal mucosa (M) during feeding and this securely anchors the worm. The buccal capsule (B) is lined with cutting plates or teeth that allow the parasite to penetrate through the mucosa.
Many parasites combine a variety of attachment devices. The trematode Petasiger has oral spines, oral and ventral suckers,and body spines.
The tapeworm Tatria has scolex suckers, a rostellum with large hooks, and lateral projections on the proglotids.
The tapeworm Triaenophorus possesses bothria on its scolex, but these probably assist only in the initial attachment of the parasite to the villi (V). The parasite soon uses its scolex hook to penetrate the surface. This stimulate a host response that results in loss of villi and the proliferation of connective tissue (C) around the scolex. The parasite scoleces (P) are now anchored securely
Proteocephalus uses its scolex suckers to grip the epithelium. The scolex attaches deep within the crypts, providing additional protection against abrasion.
Echeneibothrium has four leaf-like phyllidea (arrows) that are each covered in loculi (L). The shape of loculi in various related species seems correlated with the surface topography of the region of the intestine in which they live.
One of the more unusual means of attachment is displayed by the nematode Heligmosomoides. The body forms a coil that wraps around villi like a spring. The secure attachment is necessary because this parasite live near the pylorus, where peristaltic activity and fluid currents are at their maximum.
Most intestinal protozoans do not possess specific attachment organs. They are mobile and simply swim or crawl along the epithelial surface or in the contents. Giardia possesses two sucking disks, which in combination with flagellar action create a suction that adheres the parasite to the epithelium of the host.
