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!