The rhizoplast (also known as internal flagellar root, fibrous root or cross-banded root)[1][2][3] is an organelle present in a variety of flagellates, including ochrophyte and chlorophyte algae and some fungi. This term is used for a variety of striated, fibrous root-like structures that attach to the basal bodies (kinetosome) of the flagella and end in some other organelle. In the strictest sense, the term refers specifically to a type of root (known as system II fiber) that is composed of contractile microfibrils of centrin and connects directly to the surface of the cell nucleus.