Six of a kind

This is one of my favorite marine snails, but they're small (usually less than 4 mm long), so they're often under-appreciated. They occur in Bodega Bay, but I found a few washed up on a beach in Pacific Grove yesterday, so I tried to photograph several of them.  

One of the most fascinating things about this species is the variable color pattern — although there are "themes," almost every shell you find is unique.

Meet Eulithidium pulloides (formerly Tricolia pulloides).  Here are six separate examples.

Sometimes the shells are relatively solid: 

 

Other individuals have large pale splotches:

 

Some have more swirled patterns: 

 

And others have bolts and zigzags of color:

 

Sometimes you have to look closely for the very fine stripes: 

 

Other times there are paisley-like prints: 

 

For comparison, here are all six of these individuals together.  Note the sand grains in the picture.  The largest of these snails was 3 mm long.

 

The Light and Smith Manual (2007) says that Eulithidium pulloides is found "in gravel, under rocks, or associated with surfgrass or algae."  I also located one reference that noted their occurrence with subtidal coralline algae.

I wish I knew more about this species, especially the reason for such variable shell patterns!