Fimbriae (sometimes called attachment pili) are fine filaments of protein, usually 210 nanometres in diameter and up to several micrometers in length.

Their common name denotes the threadlike slender body which allows them to virtually disappear among the fine filaments of seaweed, hydroids and bryozoans.

Cells lining the walls of these ventricles contain fine filaments, and the cells are covered with a fine gelatinous layer.

The tip links are made up of nearly vertical fine filaments that run upward from the top end of a shorter stereocilia to its taller neighbor.