22 February 2010

Shell color and shell repair in Batillaria minima

One of my favorite intertidal snails is Batillaria minima, already a subject of several posts, including this one and this one. Back in 2006, I published a short paper on shell repair in Batillaria minima and its relation to the retractibility of the snail into its shell (see this post for details).

At 2 locations near Tampa, Florida where I've been studying Batillaria minima, most snails have black shells. Occasionally, there are individuals with lighter colored shells, usually with green or brown tints. I suspect the green color is contributed by the microscopic algae growing on the shells.

Usually, ~20% of shells have repaired body whorls and ordinarily, the repaired portion of a shell is black like the rest of the shell. Here are 2 such shells; in the lower shell, the repaired portion is slightly lighter with a greenish tint.


Now here is a shell in which the repaired portion of the body whorl acquired a color much lighter than the original shell.


And here is a shell in which the opposite happened: the original shell had a light brown-green color, while the repaired portion ended up with the usual black color.


Finally, here is a shell displaying a peculiar color change. Something happened while the snail was building its penultimate whorl and the shell color suddenly changed from light green to pitch black. The spire also became slightly crooked, indicating that the snail had probably suffered some injury, but survived it.


I don't know the anatomical basis of how an injury triggers a change in shell color.


Wallace Ward said...

Curious. I wonder if injury to and then healing of the underlying mantle activates/inactivates some genes.

fred schueler said...

Is it far-fetched to suggest that the shell colour is due to diet, and that the injuries may be due to attempted predation that moved the snail out of its previous habitat to a place where a different diet was present?


It is probably due to the turning on/off of pigment cells as a result of either genetic or physiological changes. They are not very active snails & I don't think they could move far enough following an injury to change their diet.

Wanderin' Weeta said...

I've seen that extreme colour change in one of my batillaria shells (now housing a hermit crab). I wondered what caused it.

I'll keep a closer eye on shell colour and shape from now on.

Anonymous said...

I am assuming that these shells show damage from unsuccessful predation attempts. Who is the predator? Is it crabs? Birds?

The radical change in color is a really interesting phenomenon, especially the one where the shell changed from light to dark.

Susan J. Hewitt


The predators were probably crabs.

Torsion81 said...

I wonder if the snail was dispersed to a different habitat/substrate and the result was a change in shell color.

See Manriquez et al. 2009. Adaptive shell color plasticity during the early ontogeny of an intertidal keystone snail. PNAS 106:16298-16303


I don't think that is very likely in this case, because, as I wrote above, they are not very active snails & I don't think they could move far enough following an injury to change their diet.