is this a problem

[Sweetpea]

I agree 100% - we are a family here!

I have a similar critter in one of my tanks - it only opens up a tiny bit, and from what I can see, the inside filtering part looks purple-ish. It has been very happy in a fish-less tank for over a year with feeding catered to corals.

[JustDavidP]

Here are a couple of my hitch-hiking bivalves. This spiny oyster does NOT bore...but sits atop a rock where I noticed it a year or so ago. It has increased in size by 10 fold since then. Hendrix, my mandarin, is always around it, it must be his safety blanky



Here's a more typical "boring clam". This one is in a refugium in a rock.



Dave

[pass1over]

I used to have about a dozen bivalves just like the one in the original pic. The hinge was always on the outside and it lo0ked like they were "biting" the rock.
They do only open a little but seem to be open nearly all the time. GREAT filter feeders, wish soe of mine hadn't died off