- Kingdom: Animalia
- Phylum: Cnidaria
- Class: Anthozoa
- Subclass: Octocorallia
- Order: Pennatulacea
- Suborder: Subsessiliflorae
- Family: Pennatulidae
- Scientific name: Pennatula phosphorea
- Norwegian: vanlig sjøfjær
The common sea pen can grow to a height of 40 cm. With its deep red color it is easily distinguished from other sea pens. There is a highly developed muscle and neural system in the stem, enabling the colony to "walk" along the bottom in search for a better location.
This is a very common inhabitant on sandy or muddy substrate, on depths ranging from 10 to 100 meters. It is most frequent deeper than 20 meters.
It is widespread in North-East Atlantic Ocean as well as in the Mediterranean.