Shells brightly coloured/patterned to attract mates?

[paul monfils]

Hi,

Sexual dimorphism occurs in a few shell-bearing molluscs, like Cassis cornuta and Lambis lambis, but not very many.  And it doesn't involve the color or pattern, just the physical structure of the shell.  It is not likely that the color patterns of mollusc shells are involved in attracting a mate, for the following reasons:
- The eyesight of most mollusks is poor, probably not able to distinguish much more than light vs. dark areas.  Even cones find their prey primarily by smell.
- In life, the shell of most brightly colored species is covered with a fibrous periostracum secreted by the animal, which obscures the color and pattern of the shell.
- Many brightly colored species live in deep water where there is virtually no light.  Even in water of moderate depth the warm colors (red, orange, yellow) are not visible because those colors of light do not penetrate that far into the water.