a . E. Lendell Cockrum and William J. McCauley, Zoology (Philadelphia: W. B. Saunders Co., 1965), p. 163.
u Lynn Margulis and Karlene V. Schwartz, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth (San Francisco: W. H. Freeman and Co., 1982), pp. 178–179.
u Perhaps the simplest forms of multicellular life are the Myxozoans, which have 6–12 cells. While they are quite distinct from other multicellular life, they are even more distinct from single-celled life (kingdom Protista). [See James F. Smothers et al., “Molecular Evidence That the Myxozoan Protists are Metazoans,” Science, Vol. 265, 16 September 1994, pp. 1719–1721.] So, if they had evolved from anywhere, it would most likely have been from higher, not lower, forms of life. Such a feat should be called devolution, not evolution.
Colonial forms of life are an unlikely bridge between single-celled life and multicelled life. The degree of cellular differentiation between colonial forms of life and the simplest multicellular forms of life is vast. For a further discussion, see Libbie Henrietta Hyman, The Invertebrates: Protozoa through Ctenophora, Vol. 1 (New York: McGraw-Hill, 1940), pp. 248–255.
u Nor do Diplomonads (which have two nuclei and four flagella) bridge the gap. Diplomonads are usually parasites.