Figure 4. The flagellar structures of the unicellular choanoflagellate more closely resemble those of multicellular opisthokonts than unicellular organisms from other suprakingdoms.

Isosurface renderings of the 96 nm flagellar repeats from unicellular (top row) vs. multicellular (metazoan; bottom row) species. The summary on the bottom right highlights that the flagella of opisthokonts, including the unicellular/colonial S. rosetta, contain two dynein heads per ODA and reduced (R) radial spoke (RS) heads, whereas Tetrahymena (Alveolata) and Chlamydomonas (Archaeplastida) contain three dynein heads per ODA and broad-shaped (B) RS heads. The dynein heads in each ODA are indicated with black arrowheads and are pseudocolored in pale and darker purple, and in magenta where a third dynein is present, to help distinguish between ODAs with two or three dynein heads. Each organism contained one double-headed and six single-headed inner dynein arms (IDAs). The averaged axonemal structures from species other than S. rosetta were previously published (Lin et al., 2014).