List of prehistoric sea cucumbers

Naming conventions and terminology

• Junior synonym: A name which describes the same taxon as a previously published name. If two or more genera are formally designated and the type specimens are later assigned to the same genus, the first to be published is the senior synonym, and all other instances are junior synonyms. Senior synonyms are generally used, except by special decision of the ICZN, but junior synonyms cannot be used again, even if deprecated. Junior synonymy is often subjective, unless the genera described were both based on the same type specimen.
• Nomen nudum : A name that has appeared in print but has not yet been formally published by the standards of the ICZN. Nomina nuda are invalid, and are therefore not italicized as a proper generic name would be. If the name is later formally published, that name is no longer a nomen nudum and will be italicized on this list. Often, the formally published name will differ from any nomina nuda that describe the same specimen.
• Nomen oblitum : A name that has not been used in the scientific community for more than fifty years after its original proposal.
• Preoccupied name: A name that is formally published, but which has already been used for another taxon. This second use is invalid and the name must be replaced. As preoccupied names are not valid generic names, they will also go unitalicized on this list.
• Nomen dubium : A name describing a fossil with no unique diagnostic features. As this can be an extremely subjective and controversial designation, this term is not used on this list.

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