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Swedish Sponge fauna last updated happened over 80’s years ago. This fact explains, partially, the country’s low sponge. In this thesis, I update our knowledge of the swedish demosponge fauna (Paper I and II) and, give an insight to the relationship within one of the most common sponge groups in the country belonging to order Suberitida (Paper III and IV), as well as to investigate possible dispersal barriers for freshwater sponges (Paper I). I relied on my own sampling, museum specimens and the marine inventory by STI. In total, we found nine new reports for Sweden (one freshwater and eight in sea water) and one new species to science (sea water). In the freshwater survey using Spongilla lacustris (Paper I) we tested if catchment areas represented dispersal barriers, but with the marker used we could not observe a clear population structure. For the marine environment the collected material contained what appear to be several species Suberites (Paper II). This genus, and many taxa within the order, is known for a paucity of morphological characters and long taxonomic history. This while being known for not representing a natural group. Thus, in order to know what species of Suberites present in Sweden we had to answer: What is the circumscription for the genus? What are its relationships with other suberitids? What are the oldest available names for the genus and the species within?

In Paper III, we use phylogenetics to infer the relationships within Suberitida. The trees showed two separate clades for Suberites - A and B. Clade B was together with the genus Aaptos, a Homaxinella species and Stylocordyla - family Stylocordylidae and, given that result we argued for expansion of Stylocordylidae. In Paper IV, we did an extensive literature review of the senior names for clade A and B. Plus, we presented species delimitation and their names for 30 species found in the Northern Temperate Atlantic realm. We argue for the resurrection of Syringella as the name for clade B. While, in clade A (under the name of Suberites), we make the case for S. ficus proper name to be S. subereus and, we solved the homonymy with the name S. virgultosus by naming the species found by Bowerbank - Suberites sp. ”misterbeanii”.