07 February 2011

Cerithidea scalariformis and how far it withdraws into its shell

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.

1 comment:

Anonymous said...

Very interesting Aydin! I suppose maybe that might also be true of a lot of species in the other very high-spired families within the Cerithoidea?

I was also wondering, about their locomotion... I did used to watch Cerithidea californica in southern California, in the flood control channel of the San Diego River, but that was way back in 1970, and I hardly remember. Do they move around and feed when the water is just a couple of mm deep on the mud flats on which they live? if so then maybe that would help lift the shell just a little bit off of the substrate?

Susan J. Hewitt