Stomotoca atra is a hydrozoan medusa (family Pandeidae) found in cold temperate and boreal coastal waters of the North Pacific, a moderately sized, darkly pigmented hydromedusa bearing four tentacle clusters and four radial canals with distinctive gonads arranged along them for reproductive output in the pelagic zone. The species feeds on copepods and other small zooplankton and is a component of nearshore gelatinous zooplankton communities. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.