20 June 2006

Yet another snail at the edge: Cerithidea scalariformis


An earlier post in this series of snails that live at the edge of the sea (or land, depending on which way evolution is taking them) was about Batillaria minima. Compared to the latter, however, Cerithidea scalariformis is quite a terrestrial snail. Unlike B. minima, but like Littoraria irrorata, C. scalariformis is active out of the water; in fact, if it is placed in water, it crawls out of it (more on that in the future).


Cerithidea scalariformis has been recorded from South Carolina thru Florida down to Cuba, Mexico and Panama.

cerithidea1The photo on the left shows the roughly circular, soft and horny operculum of C. scalariformis. Thomas Say, who described this species in 1825 as Pirena scalariformis (Say’s paper), usually had very little to say about the anatomies or habits of the species he wrote about. But, in this case, he included an interesting observation: “…the operculum is orbicular, and so small as to admit of the animal retiring one half the length of the shell.” I believe what Say meant is that the snail can withdraw as deep into its shell as one half the length of the shell. When I examined these snails near Tampa, Florida, earlier this month, I noticed that they could indeed withdraw deeply into their shells, but because their shells are opaque, I could not tell just how deep they could go in.

More information on C. scalariformis is available at the web page of the Smithsonian Marine Station at Fort Pierce.


Vasha said...

I see that C. scalariformis is another snail with a "snout". Kind of cute. That's interesting to me. Since the only live snails I'd previously seen close up were pulmonates, I'd somehow just assumed that all gastropod molluscs looked like that. But you show ones with snouts, with eyes not on tentacles, and more. No doubt marine species have yet more variations of form? Can you suggest somewhere to see pictures of them?


Most marine snails, the "prosobranchs", have snouts.

Sorry, I don't know where there are pictures of them.