This catalogue presents a fairly complete inventory of 2214 species, subspecies and varieties, most of them named to the species level of metazoan invertebrates recorded from the Gulf of St. Lawrence, the St. Lawrence Estuary, and the Saguenay Fjord. Benthic, Planktonic, nektonic and parasitic species are covered, as are some salt-tolerant freshwater species. All faunistic records for each species have been accurately documented. The most recent, complete, well-illustrated and key-supplied references available have been provided, in order to facilitate identification and back up the synonymy. In a voluminous alphabetical index, the nomenclature is cross referenced to all the names of the higher taxa, genera, species, and old synonyms and misidentifications reported for the Estuary and the Gulf. A numbered bibliography containing 1910 titles of references and other faunistic (e.g., collections) or taxonomic sources is provided to support the many citations.