Found on Maenporth, Falmouth, Cornwall beach
No interactions present.
Not sure about the worm though...
Your photo shows three different species (in fact three different phyla). The oyster (a mollusc), a tube-dwelling annelid worm (probably Pomatoceros triqueter) and a boring sponge (probably Cliona celata). All 3 are invertebrates so you could classify your observation as "Invertebrate" rather than "?". You could also repost the observation (twice!) if you want to highlight and establish the id. of the worm and the sponge!
Appears to be a Pomatoceros species. Two species turn up regularly in UK and are best separated by looking at the shape of the operculum. That can't be done with only an empty tube to look at.
On the tube of P tiqueter there is a single median ridhe while on the tune of P.lamarcki there ridge is flanked on either side by a less distinct ridge.
In the picture only the median ridge is clear and so P triqueter is the most probable ID
Jonathan, Mike and Derek are correct here, there isSpirobranchus triqueter which used to be Pomatoceros triqueter.
This is a lovely specimen which does not show the triangular overall shape but does show a key feature - a single median ridge.
I supsect Mark that you've left the arena (iSpot) which is a shame because the picture is excellent and has generated some interest but still needs moving to Invertebrates.
See my recent post here
Lat/Lng: 50.1257, -5.0944
OS grid ref: SW789296
Washed up on the beach