From Ed Haviland
 
I'm bringing up this subject, I guess I'm trying to find out the pros and
cons whether or not these shells have any instinct or intelligence at all
or is there a rational explanation of what certain aspects of their life
mean. First, let us wonder if the Spondylus egg or veligers think of what
to light on or do these veligers only roost on surfaces that are rough and
landing on a smoother or slippery surface does not mean a successful perch
and continued life.
Second, have you ever noticed that Spondylus with a smoother, perfectly
flat bottoms as the ones that have grown up on the side of a metal ship or
oil rig pillar almost always have a produced bottom valve, that is, it is
larger than is normal and always larger than the top valve which isn't so
when the shell is attached to rough or dead coral.  The question is: Is
this a safety behavior on the part of the shell or not?
Years ago the late Sozon Vudikiotis of Tarpon Springs who had collected
many Spondylus americanus while sponge diving in the Gulf of Mexico got on
the subject and said he found the thornys at 17fms and those were usually
imperfect as they were firmly attached to rocks or dead coral and mostly
full of worm holes. At 19fms. many more unattached or attached to a pebble
or small piece of rock and lying on the bottom, he maintained these were
perfect specimens with few or no worm holes. Does anyone have an
explanation?
How you Emilio my old friend?
Ed Haviland