Bivalve vs Gastropod

[hkirk1]

I have read where there are more than 4 times the number of species of gastropods than bivalves.  If this is true, then why do I mostly find bivalves on the beach and not gastropods?

[david_admin]

Hello,

Even if there is 4 time more (I did not check), when you go to a beach, just in front it is usually sandy areas, and there you will find mostly bibalves... that is the main logic reason. And I can say that in France, on sandy bay you will mainly find dead bivalves and on rocky shorelines you wil lfind a lot gasteropds...

Though, you must consider also degres of rarity of shells, you can have more species but they are all rare... versus less species but much more common...

Hope that help you,
DAVID

[Marlo9]

Keep this in mind.  For every "bivalve"  there are two valves to wash up on the beach.  So, your ratio is really 2:4, not 1:4. 

Bivalves are lighter and flat and rise far more easily in roiling water, thereby being more likely to make it to the shore.  They also tend not to roll back down the shore to the water.

Far more univalves are "micro" size and are not readily visible on the beach (or have been so rolled around on the way that they are not recognized as shells.

Most of all, univalves are more highly prized and all the other collectors got there before you and took them home.