Sphaeromyxa artedielli sp. n. is described from the gall bladder of the Atlantic hookear sculpin Artediellus atlanticus Jordan et Evermann (Cottidae; type host) from northern Norway. The parasite was also found to infect Triglops murrayi Günther (Cottidae). Spores are produced in disporic pansporoblasts in large flat plasmodia. Spores are straight and fusiform with truncated ends, and measure 16.5-18.7 µm × 4.9-6.2 µm. Valves are thick, striated and suture line is straight. Two equal ovoid polar capsules measure 4.2-6.8 µm × 2.9-4.4 µm and contain irregularly folded polar filaments. Distinctive features include spore shape and size, spore length/width relationship, striated valves, equal polar capsules and a short intercapsular distance. Sphaeromyxa bonaerensis Timi et Sardella, 1998, Sphaeromyxa cannolii Sears, Anderson et Greiner, 2011, and Sphaeromyxa sevastopoli Naidenova, 1970 produce straight spores with truncated ends that are of similar length as those of the new species. Sphaeromyxa cannolii differs in showing smooth spores with unequal polar capsules. The new species differs from S. bonaerensis and S. sevastopoli in significantly wider spores and polar capsules. Sphaeromyxa balbianii Thélohan, 1892, a species originally described with significantly smaller spores than S. artedielli sp. n., has previously been recorded from T. murrayi. We show that S. artedielli sp. n. differs from S. balbianii from the type host Gaidropsarus vulgaris (Cloquet) by its SSU rDNA sequence, and suggest that Atlantic records of Sphaeromyxa spp. from T. murrayi represent S. artedielli sp. n. The closest relative to S. artedielli sp. n. according to the SSU rDNA sequences, S. longa Dunkerly, 1921, differs clearly by spore size and shape. In the SSU rDNA-based phylogenetic analyses, S. artedielli sp. n. groups with other Sphaeromyxa spp. with straight spores and truncated ends in a clade that represents a sister-group to Sphaeromyxa spp. with arcuate spores and rounded ends. Our results indicate that an SSU rDNA pseudogene is present in S. balbianii.