I have a Spondylus varians (water spondylus) that probably exceeds 80mm near
the hinge (for the top valve). But the big Tridacna gigas has got to be the
tops in this category. I have a little two footer and moving it is almost like
carrying a sack of concrete. Someone out there with an old bird bath or water
fountain needs to measure the thickness. It will probably exceed 100mm.
Tom Eichhorst in New Mexico, USA