To avoid confusion it is important to avoid publishing a species name which is the same as one which has already been used for another species (a homonym). For example the crab names Cancer strigosus Linnaeus, 1761 and Cancer strigosus Herbst, 1799 are homonyms. Usually the younger name is invalid and has to be renamed to avoid confusion (Chapter 12).
The classic works of zoological nomenclature should be checked first, e.g. Index Animalium. For many groups of animals there are recent catalogues which can be checked to see which names have already been used. E.g. for mammals: Wilson and Reeder (2005) Mammal species of the World. Hopkins University Press. There are also web catalogues e.g. for fish - www.fishbase.org; for animals but with varying coverage - Integrated Taxonomic Information System www.itis.gov, and Animalbase www.animalbase.org; and for literature containing descriptions of new species - Zoological Record® database, http://thomsonreuters.com, available through specialist libraries. In some cases it is necessary to undertake a library search to trace species names in the original literature.