Pennatula phosphorea is a sea pen forming erect colonies of up to 40 cm
tall. Swollen with water, they are fleshy and slightly bent over the surface. The bulbous stalk
embedded in sediments is only visible in its upper part. Above the surface, a 25 cm tall rachis
have numerous alternate opposite branches on each side of the central axis. They are triangular
in cross-section in a leaf-like shape. Each
branch has about fifteen autozooids regularly spaced, opening on the ventral side of the colony.
Tiny siphonozooids are laid on each side of the central axis, in broad rows on the
dorsal side, in narrower lines and extending a little between the branches on the ventral side.
Colonies are retractile and may withdraw within the sediment or be more or less swollen above the
They are yellowish to pale pink with reddish shades due to deep blood-red sclerites concentration.
When stimulated, the colony has a blue-green luminescence.
Pennatula phosphorea is found in muddy and sandy bottoms from 10 to at least 100 meters deep, in the North-East Atlantic, the North Sea and probably the English Channel and in the Mediterranean Sea.
(source : European Register of Marine Species)
Colony : Group of several individuals of the same species. There, the colony has several individuals,
the polyps, but the whole colony is considered as the animal.
Polyps : Within these colonial animals, the polyp is the individual.
Rachis : Upper part of the Pennatulacea bearing polyps.
Autozooids : Specialized polyps in charge of catching food.
Siphonozooids : Specialized polyps without tentacles in charge of driving water into the colony.
Sclerites : Tiny calcareous elements forming a loose squeletal frame.
Top photograph :
© Mat Vestjens. Published with author's kind permission :
Pennatula phosphorea, Oban, West Highlands, West Scotland. Depth 16 meters.
Text : Wilfried Bay-Nouailhat © 2008-2017.
Translation : Anne Bay-Nouailhat © 2008-2017.