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.
- Aruga J, Odaka YS, Kamiya A, Furuya H (2007). "Dicyema Pax6 and Zic: tool-kit genes in a highly simplified bilaterian". BMC Evol. Biol. 7: 201. doi:10.1186/1471-2148-7-201. PMC 2222250. PMID 17961212.CS1 maint: multiple names: authors list (link)
- Pawlowski J, Montoya-Burgos JI, Fahrni JF, Wüest J, Zaninetti L (October 1996). "Origin of the Mesozoa inferred from 18S rRNA gene sequences". Mol. Biol. Evol. 13 (8): 1128–32. PMID 8865666.CS1 maint: multiple names: authors list (link)
- Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 248–249. ISBN 0-03-056747-5.