Dicyemidae

Dicyemidae, a family of very lowly multicellular organisms, parasitic in habit. They are found in cuttle-fishes, while related organisms known as Orthonectida occur in a brittle-star and in a Nemertean worm. Professor E. van Beneden has included them all under the title Mesozoa in contrast to the lower (single-celled) Protozoa on the one hand, and the higher (many-celled) Metazoa on the other. The largest species of the genus Dicyema measures 5-7 millimetres; the smallest is ten times less. These organisms hardly rise above the level of the embryonic gastrula, and some seem hardly to attain it, but it is still uncertain how much of this simplicity is primitive, and how much the result of degeneration. See E. van Beneden and C. Julin, Archives de Biologie (1882); Whitman, Mitth. Zool. Stat. Ncapel (1883); Braun, Centralblatt Bacteriol. (1887).