In the accepted names of taxa, infraspecific categories are optional. Synonyms which have infraspecific rank may be required even if the accepted taxon is a species. The primary purpose of the Register is not to serve as a complete nomenclatural resource. Thus, for example, the inclusion of basionyms is not essential. However, the kind of synonym, where known, can be specified.
Common names are optional.
Other data Geographical data is optional and may be added later after the initial checklists have been created. This could be done either during the ERMS project or later in a subsequent project. To record distribution, whatever area names are available should be used, without attempting to create a standardised system or use coordinate data. The main purpose of the geographical data is to validate the inclusion of each species in the European list, not to document its precise distribution. However, for many purposes it is useful to record whether a species occurs in the Atlantic Ocean or the Mediterranean Sea.