Source Conn. D. B. and Z. Swiderski. 2008. A standardised terminology of the embryonic envelopes and associated developmental stages of tapeworms (Platyhelminthes: Cestoda). Folia Parasitologica 55: 42-52.
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Hexacanth – a six-hooked larva derived from micromeres, which is the definitive product of embryogenesis of a cestode, and that invades the first or sole intermediate host.
Oncosphere – a hexacanth enclosed by one or two embryonic envelopes. – a hexacanth enclosed by one or two embryonic envelopes.
Coracidium – a hexacanth enclosed only by a ciliated inner envelope that provides a mechanism for free swimming.
Embryonic envelopes – the two syncytial envelopes derived from blastomeres and completely enclosing developmental stages from the late cleavage embryo through the fully formed hexacanth larva.
Outer envelope – the outermost embryonic envelope, derived from macromeres and enclosing all other embryonic and larval components. This envelope generally undergoes apoptosis early in embryonic development, and prior to final morphogenesis of the hexacanth.
Inner envelope – the innermost embryonic envelope, derived from mesomeres and enclosing micromeres and ultimately the hexacanth. This envelope generally persists throughout embryonic and larval development, and thus may be considered part of the fully formed larva.
Embryophore – name applied both to the full ciliated inner envelope of a coracidium, and to a specialised intracellular proteinaceous lamina produced within the inner envelope of a cestode with a non-swimming oncosphere. (Note: some authorities prefer to distinguish the motile inner envelope of a coracidium by referring to it as a "ciliated embryophore".)
Vitelline capsule – a thin proteinaceous layer that forms from coalescence of material released by exocytosis from one or more vitellocytes near the time of fertilisation, and that quickly encloses the vitellocyte(s) along with a single oocyte and a single sperm. Depending on the species, this layer may or may not persist through embryogenesis.
Shell – sclerotin proteinaceous material that is secreted by vitellocytes and is deposited on the inner surface of the vitelline capsule prior to hardening by a polyphenol/quinone tanning process. This occurs in cestode species that have a large number of vitellocytes per oocyte (i.e., polylecithal). The hardened shell typically encloses the oncosphere outside the host.
Outer coat – proteinaceous or other material that is secreted by the oviduct and/or uterus and is deposited on the outer surface of the vitelline capsule in some cestode species that have one or few vitellocytes per oocyte (i.e., oligolecithal).