van Beneden, 1876
Classification is controversial. They are probably a new phylum. Traditionally, dicyemids have been grouped with the Orthonectida in the Mesozoa. However, molecular phylogeny indicates that dicyemids may be more closely related to the roundworms.
Adult dicyemids range in length from 0.5 to 7 millimetres (0.020 to 0.276 in), and they can be seen through a light microscope. They have eutely: each adult individual of a given species has the same number of cells. Cell number is a useful identifying character.
The asexual stage is termed a nematogen; it produces vermiform (worm-like) larvae in the axial cell. These mature through direct development to form more nematogens. Nematogens proliferate in young cephalopods, filling the kidneys. Later, as the hosts mature, sexual forms called rhombogens are formed. They are hermaphrodites, with gonads of both sexes. The rhombogens self-fertilise, and later release larvae.
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- Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 248–249. ISBN 0-03-056747-5.