The affinities of honeycomb or sandcastle worms (Sabellariidae, Polychaeta) and other polychaetes are studied using morphological and DNA sequence data (18S rDNA, 28S rDNA, and EF-1 alpha). Maximum-parsimony analyses were performed including 20 terminals and 7155 aligned characters. The monophyly of Sabellariidae is confirmed and well supported and sister-group relationships with Spionida are suggested but only poorly supported. Phylogenetic relationships within Sabellariidae are also assessed for the first time, using morphological data. Maximum-parsimony analyses of 30 terminals and 31 characters were performed with and without weighting the less homoplasious characters. Implied weighting resolved polytomies recovered after non-weighting datasets and suggest that the established sabellariid subfamilies are not monophyletic and that the number of parathoracic segments is homoplastic. Instead, some opercular features and chaetal characters not often incorporated in descriptions are here shown to be phylogenetically informative and support some of the clades recovered. We provide a description of morphological features of sabellariid and previously related groups together with illustrations that will, we hope, be used as a baseline for further systematic and taxonomic studies in the group and as a framework for future molecular studies. Generic diagnoses and a description and a key to genera are provided.
