I know, it's been way too long since I've posted a picture of clam siphons. ;) At least that's what Tim would say!
I photographed these siphons in a rocky crevice at low tide this afternoon. They were under water at the time. Do you remember which is the inhalant siphon (pulling water in) and which is the exhalant siphon (pushing water out)?
The siphon on the left, with all of the frills, is the inhalant siphon, while the siphon on the right, with the more volcano-like opening, is the exhalant siphon.
I showed a clam similar to this on 9 August 2013, but those pictures were taken under a microscope (click here to review them). I thought it would be worthwhile to show you what the siphons would look like if you encountered them along a rocky shore.
Although I'm not sure 100% sure, this might be a Flat-tipped Piddock (Penitella penita). But let me know if you think it could be a different species.