- Kingdom: Animalia
- Phylum: Cnidaria
- Class: Hydrozoa
- Subclass: Hydroidolina
- Order: Leptothecata
- Family: Laodiceidae
- Scientific name: Staurophora mertensii
- Norwegian: korsmanet
Hydroid stage: The hydranths are approximately 1 mm and hardly visible for scuba divers.
Medusa stage: The bell is large, the diameter may reach 30 cm. The shape is flattened, the height is approximately 1/8 of the diameter. The stomach, mouth and four radial canals form a large cross, nearly reaching the umbrella margin. There are a large number of marginal tentacles.
The hydroid is probably coastal. The medusa has been found on all depths, from the surface and down to a depth of 150 meters.
This species is considered bipolar, existing both in the Arctic as well as Antarctic. In the North Atlantic ocean it can be found as far south as the North Sea.