Colonies much stouter and more fleshy than other British sea-pens, up to 400 mm long. Fused autozooids form large triangular leaves arranged more or less alternately in two opposing lateral rows. Siphonozooids occur in a broad band on each side of the naked dorsal tract and a narrower band each side of the ventral tract, extending a little between the leaves but never on to them.
Colouration: Sclerites long and slender, deep blood-red; they are responsible for the general colour of the colony. The flesh is translucent, yellowish or pale pink; anthocodia of the autozooids white. Axis white, often bent over at its ends like a shepherd's crook.
In sandy or muddy substrata, usually in depths exceeding 10 m, probably extending into water deeper than 100 m.
Frequent to common in the North Sea and around western Scotland; no records from southern Britain. This species is widespread in the North Atlantic and the Mediterranean but its full range is uncertain due to probable confusion with other species.