In the previous post, I wrote about how small the foot of the intertidal snail Cerithidea scalariformis was relative to the length of its shell. Then I hypothesized that having a small foot probably enables a snail to withdraw its body deep into its shell when and if its aperture comes under attack by a predator. At the end of the post, I noted that I didn't know how far into its shell Cerithidea scalariformis could actually withdraw. Last night I went thru my notebooks and found some relevant information.
A few years ago, I attempted to keep a small number of Cerithidea scalariformis in captivity. But the snails didn't seem to do well and remained in their shells most of the time. Nevertheless, this gave me a chance to note how far into their shells they were withdrawing. Here is one live snail whose body was about one half whorl behind the aperture. This was indicated by how far into the shell light shone thru the aperture could penetrate.
When forced, Cerithidea scalariformis can probably withdraw even deeper into its shell. I suspect it can withdraw at least one whorl away from the aperture. Curiously, though, among the several hundred live snails I examined in Florida, only a few had repair scars in the body whorls of their shells. This may mean that they either don't have major predators, or, despite being able to withdraw deep into their shells, only a small fraction of snails survive predator attacks and repair their shells.