Phylum Annelida are ubiquitous metazoans found in almost every terrestrial and aquatic habitat on Earth. Historically, taxonomic studies on the phylum have been focussed largely on its major groups – polychaetes, oligochaetes and leeches – so that while family-level keys for each group are available, no single-source identification guide exists to the world’s annelid families. Here we provide the first illustrated linear key to annelid families and update family-level descriptions and diagnoses that distinguish individuals of each family from those of other families in the phylum. This information is generated from an annelid DELTA database of 331 characters and 166 mostly family-level taxa. We provide a link to downloadable software (ANNiKEY) allowing the same data to be interrogated using the open-source DELTA program Intkey, which enables both interactive identification and taxonomic query functionality. For each family-level taxon we provide a diagnosis, full description, links to taxonomic data at World Register of Marine Species, illustrations of diagnostic features, and a summary of the recent literature including a list of published keys to genera and species.

annelid, ANNiKEY, computer taxonomy, DELTA, diagnosis, linear key, interactive key, natural language descriptions, taxonomic verification