We propose to combine traditional taxonomy based on detailed morphological analyses with molecular methods to investigate the N Atlantic and Arctic deep-sea calcareous sponges (Porifera, Calcarea). Unfortunately Calcarea offer very few morphological characters for reliable (informative) phylogenetic analysis, and their morphological characters appear to be highly susceptible to convergence. The calcareous sponges have got a reputation of being obscu re and taxonomically difficult, and no comprehensive work has been done on this group in the deeper part of the north Atlantic and Arctic Oceans. Some more effort has been put into the shallow water calcareous sponge faunas, but also here the recent work by Rapp is the first comprehensive work done in almost 100 years. The result is that the taxonomy of calcareous sponges in the Atlantic and Arctic oceans is out of date and poorly understood, and there is a striking need for revision of the older work. Re cently the use of numerical analysis of shape, size and distribution of spicules, combined with detailed histological work have thrown new light on the classification of the Calcarea. As a result the species diversity of the calcareou sponges is indicated to be much higher than was previously expected. Molecular data appear to be essential to provide corroboratory evidence for phylogeny based on morphological hypotheses. Basically the general knowledge about deep-sea calcareous sponge s is very restricted, and this is the first attempt to investigate this taxonomically difficult group with a molecular- and phylogenetic/phyleogeographical approach.