Catablema vesicarium is a hydrozoan medusa (family Mitrocomidae) found in cold boreal and subarctic oceanic waters of the North Atlantic, a relatively large hydromedusa with a hemispherical bell and long marginal tentacles used for prey capture of copepods and other small crustaceans in the pelagic zone. Little is known about the benthic hydroid stage of this species, which is typical of many hydromedusae with poorly characterized polyp phases. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.