Plume worm, Pherusa plumosa (NL: pluimworm) seen from below, Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
Have a look at the photo below. At first sight you can mistake this animal in situ for a sea anemone. But as you can see in the photo above, it must be something else. It has bristles, two different kind of tentacles, eyes (the two black dots at the base of the tentacles) and a warty, wormlike body. Certain sea anemones have different kind of tentacles and are wormlike. For instance Cerianthidae, like the tube-dwelling anemone, Pachycerianthus fimbriatus. But as far as I know, sea anemones never have bristles nor eyes.
Plume worm, Pherusa plumosa (NL: pluimworm), Dreischor-Gemaal, the Netherlands, 15-8-2016.
It is a bristle worm: Pherusa plumosa. It does not have a common name, so I propose 'plume worm'. Plume worm is also one of the common names of Serpula vermicularis, but that worm has a lot of common names as you can read in Wikipedia. But Serpula's tentacles look like a fan, not as much a plume, so I am stealing it back. A common name is also lacking in Dutch and I propose 'pluimworm'.
Plume worm, Pherusa plumosa (NL: pluimworm) and a very small specimen of the mud sagartia, Sagartia troglodytes (NL: slibanemoon), Dreischor-Gemaal, the Netherlands, 15-8-2016.
My attention was drawn by a post by Patrick Van Moer on the Facebook page of Stichting ANEMOON on 9 August this year. He showed a few beautiful worm species, which I had never seen before. As I became more interested in Polychaet worms (an under-appreciated class of animals) the last years, I went for a dive to Dreischor-Gemaal. Dreischor-Gemaal is a dive spot in the Grevelingen in the Netherlands, a former estuary that has become a lake due to the Delta Works.
Plume worm, Pherusa plumosa (NL: pluimworm) and Oxydromus flexuosus (NL: neonworm), Dreischor-Gemaal, the Netherlands, 15-8-2016.
At Dreischor-Gemaal the plume worm can be found from about 13 to 16 meter deep. A zone in the Grevelingen where few animals live, because when it gets warmer in summer it is almost depleted of oxygen.
The Marine Species Identification Portal mentions as habitat 'in the upper layers of the bottom; in sand or mud, eulittoral to bathyal.' Hayward and Ryland (1995; see Literature) state: 'At low water in muddy rock-crevices, amongst mussels or under stones, also sublittoral on muddy bottoms.'
At that spot I also found a few other worm species in high numbers, like Oxydromus flexuosus (NL: neonworm). In one of my next posts I will publish photo's and information about these other species.
Plume worm, Pherusa plumosa (NL: pluimworm) seen from above, Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
I collected one specimen for in vitro photo's (in vitro meaning in an artificial environment). Its length was 43 mm. At the Marine Species Identification Portal a length is mentioned of up to 60 mm for 70 segments. From the same website: 'Body long and cylindrical, covered with epidermal papillae which are better developed on the dorsal surface and around parapodia; often encrusted with sand-grains or mud.'
Tail of the plume worm, Pherusa plumosa (NL: pluimworm) seen from above, Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
What about its distribution? Marine Species Identification Portal states: 'North Sea to Baltic Sea. Possibly whole northern hemisphere.' Indeed WoRMS (World Register of Marine Species) states other places ('From other sources') in the northern hemisphere, so I googled for more. I found ZipcodeZoo, an online natural history encyclopedia. This website provides very nice distribution maps. I have copy/pasted the map of Pherusa plumosa, but the species appears to be quite cosmopolitan in the northern hemisphere, so the red dots on the map are hardly discernible. Just have a look at the page ZipcodeZoo and click here (I chose a map with 'Styling: high contrast' and 'Point size: medium').
Distribution of Pherusa plumosa (© ZipcodeZoo).
The distribution map is not flawless, because plume worms are not listed in the Netherlands. Marco Faasse wrote: 'I have found one specimen in the Oosterschelde; the species is also listed in reports of the NIOO.' It appears to be common in the Grevelingen (I found about 50 specimen in one dive), but only very recently. Ton van Haaren of Eurofins Aquasense wrote: 'We collected benthos by means of a boxcorer at 9 and 10 March 2016. In total 40 samples were taken at the Grevelingen (20 at the western and 20 at the eastern part). Pherusa was not found in any of these samples.'
Plume worm, Pherusa plumosa (NL: pluimworm), Dreischor-Gemaal, the Netherlands, 15-8-2016.
Of course the tentacles are the most obvious (and beautiful) parts of the plume worm. They are not tentacles in a sense of an organ catching food or a sensory organ: the eight largest ones are its gills.
Plume worm, Pherusa plumosa (NL: pluimworm), Dreischor-Gemaal, the Netherlands, 15-8-2016.
It also has two tentacles for catching food, called palps. You can see them sticking outwards at the photo above, searching food. The plume worm is a surface deposit feeder.
On the next photo you can see how the palps differ from the gills. The palps are very flexible, unlike the gills which are quite swollen and inflexible, like a balloon. Where the gills are rounded, the palps have a fissure with lobes. Probably to make it more easy to catch and hold food particles.
Front part of the plume worm, Pherusa plumosa (NL: pluimworm) seen from below, Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
A lot of worms, especially worms with fan-like tentacles, easily withdraw when disturbed. It is not always obvious whether this is caused by light (my shadow, my pilot light and/or the modeling light of my strobes) or the displacement of water I cause as a diver. Anyway, while diving I reduced the light to one strobe modeling light. Fortunately the plume worms appeared to be not very jumpy. Even while taking in vitro photo's, laying totally 'naked' in a petri dish, it withdrew its tentacles only while flashing.
Plume worm, Pherusa plumosa (NL: pluimworm), Dreischor-Gemaal, the Netherlands, 15-8-2016.
On the photo above it looks as if the worm has retreated in the bottom, but it has only retracted its gills and palps. See also the next photo. After a few seconds the gills are reappearing (one has to breathe), followed by the two palps (one has to eat).
Front part of the plume worm, Pherusa plumosa (NL: pluimworm) seen from below with retracted gills and palps, Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
Side view of the front part of the plume worm, Pherusa plumosa (NL: pluimworm), Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
Later I realised that what I at first thought were 'tentacles' of a tube build of particles of sand and shell, like the tube of the sand mason, Lanice conchilega (NL: schelpkokerworm), were bristles of the plume worm.
Sand mason, Lanice conchilega (NL: schelpkokerworm) with its tube of particles of sand and shell, Digue Nord, Boulogne-sur-Mer, France, 24-8-2014 (in vitro).
Bristles at the front part of the plume worm, Pherusa plumosa (NL: pluimworm) seen from above, Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
They have long, iridescent, forwardly directed bristles on the first three body parts. I presume as a kind of protection of the gills and palps. I can imagine it is not nice to have a bite in something feeling like fishbones or cat's whiskers in your mouth!
Plume worm, Pherusa plumosa (NL: pluimworm), front part seen from below, Dreischor-Gemaal, the Netherlands, 15-8-2016 (in vitro).
Once you throw a lot of light on animals like these and look at them in detail, you realize how colourful and beautiful they are. Well worth to preserve, so after a few days I released the protagonist in the sea.
I thank Marco Faasse for his (always very kind) help in identifying the worm and other information, Patrick Van Moer for sharing his photo's and information of this worm on Facebook and Ton van Haaren for information about the distribution of worms in the Grevelingen.
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