A very slender sea-pen up to 600 mm long with the axial polyp 2-4 mm in diameter. Stalk about equal in length to the rachis, or a little shorter. Sclerites are totally absent. Up to 12 autozooids on each leaf; they are long in expansion and very contractile due to the absence of sclerites. Siphonozooids are small and inconspicuous, located in a single oblique row at the foot of each leaf.
Colouration: Colouration of the whole colony varies from white to yellowish.
In muddy substrata in sheltered inshore waters, or in deeper water offshore, from 12 to 400 m depth. This species is often very abundant in sea lochs or deep, man-made harbours.
This is the commonest British sea-pen, locally abundant on all coasts but less frequent in the south. It is widespread around western Europe and in the Mediterranean and occurs throughout the North Atlantic possibly as far as North America.