B. Gastropods lay eggs which develop thru several stages.; first a trochophore then a veliger and finally a juvenile. Both the trochophore and veliger can be released early and develop further in the plankton. In order Pulmonata, to which both snails below belong, development proceeds to juvenile before hatching, ie no planktonic stage. The Battilaria appear to be marooned on an “island” of flat rocks surrounded by sand.lack
(Click photos for close-ups.)
Snails on mangrove
branches are Melampus coffeus, and they do mass like this, especially at high tide. They don't want to get wet.