Cytoskeletal and myonemal structures of dinoflagellates are made of 2–3‐nm filaments

An important cortical fibrillar cytoskeleton is described in some unarmoured dinoflagellates (Gymnodinium, Gyrodinium). The filaments which constitute this cortical layer are 2–3 nm in diameter, tightly packed, entangled, and resistant to denaturing agents. Issuing from them are other bundles of filaments which appear to be involved in the contraction of the cell, and for this reason they are termed “myonemal.” In highly contractile unarmoured dinoflagellates (Leptophyllus) the cytoskeleton is also made of 2–3‐nm filaments, but they are regularly arrayed and more directly involved in contraction and thus correspond also to myonemal structures. Both structures—cytoskeletal and myonemal—are made of 2–3‐nm filaments.