Hi

I think this shape is just a matter of how the sand collar is made, not necessarily why (as to avoid predators etc.)

 The collar reflects the sice of the female snail; the larger the snail the larger the collar.

When a female lays her eggs she rises above the sand and encases her entire shell With her foot.  Grains of sand is picked up and spread over her body until she is covered with a thin layer of sand. The sand grains are cemented together with mucous.

Then she produces the eggs, and they are Distributed evenly between her flesh and the first produced sand layer. When finished she makes a second layer of sand, so the eggs are now lying between two thin layers of sand. The last thing she does is to Escape Down, she ducks, and leaves the sand collar behind.

Kind regards, Halldis Ringvold  

Thank you very much for this answer

Best wishes

Anthony

 Thank you Dr.Halldis. I am educated by your explanation in more than one aspect! Thank you very much. Predation may be limited by such layering of eggs in a sand cage? 

Hi

I don't think the shape of the collar has to do With avoiding predators, avoiding sediment etc. but it is a matter of how the snail is built and how it is physiologically possible for it to lay eggs.

Kind regards, Halldis Ringvold

Thank you Dr.Halidis