Dicyemida

Dicyemida is a phylum of tiny parasitic animals inhabiting the renal appendages of cephalopods. Their simple bodies consist of an outer cell layer surrounding a central cell.

Nematogen: A reproductive form of dicyemid that produces additional nematogens within a cephalopod host. Nematogens multiply during favorable conditions inside the host's renal appendages.
Mesozoa: A historical grouping of simple animal parasites, including dicyemids and orthonectids. Dicyemida was traditionally classified within this group, though its status has changed.
Orthonectida: A small group of parasitic animals with simple bodies and complex reproductive stages. Orthonectids were historically grouped with dicyemids as Mesozoa.
Host specificity: The degree to which a parasite or pathogen is restricted to particular host species. Dicyemid distributions can reveal how closely parasite lineages track cephalopod hosts.
Rhombogen: A reproductive form of dicyemid that produces infusoriform larvae. Rhombogens arise as hosts mature and generate the dispersal stage.
Eumetazoa: Animals with organized tissues, distinct from sponges and several simpler lineages. Dicyemid anatomy raises questions about how its body plan relates to tissue-bearing animals.
Parasitic flatworm: A flatworm that lives in or on another organism and obtains resources from it. Their simple appearance once encouraged comparisons between dicyemids and flatworms.
Parasite transmission: The movement of a parasite between hosts or from an environment into a host. Understanding transmission is central to explaining how dicyemids colonize new cephalopods.
Infusoriform larva: A ciliated, infective larval stage produced by dicyemid rhombogens. This larva is the stage associated with transmission to new cephalopod hosts.
Cell layer: A sheet of cells forming a boundary or structural layer in an organism. The dicyemid body is organized around an outer layer and a central cell.

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