- Kingdom: Animalia
- Phylum: Mollusca
- Class: Bivalvia
- Order: Veneroida
- Family: Arcticidae
- Scientific name: Arctica islandica
- Norwegian: kuskjell
Juveniles often take a orange color. The dark blue, almost black, glossy color we are familiar with, comes with age. The shell is rounded, compared to the similar sized and colored horse mussel. It has many fine concentric growth lines. There are registrations of 220 years old individuals. It can reach a diameter of 12 cm.
It is usually buried in sand or muddy substrate, and only the shell opening and perhaps a small part of the shell can be seen. There are registrations from all depths, from the tidal zone to 500 meters depth.
It can be found from Arctic Atlantic regions to the Bay of Biscay.