We missed a bet by not calling this thread "The Color Purple."
 
In March, 1997, I had the pleasure of collecting Janthina from a beach on
San Salvador Island, Bahamas. The snails were easy to find because of the
purple splotches of dye on the white sand. In this case, there was only
about one snail per ten feet (3 meters) of beach. This was similar to the
density of Janthina that I saw on Boca Raton Island in the Florida Keys in
the late 70's. Does anyone have any idea whether the density of Janthina
has changed through time? Charles Simpson's experience in 1883 may have
been one of those extraordinary events that could still happen.
 
Janthina is said to be purple because the snails feed on purplish
by-the-wind sailors (Velella velella, harmless floating coelenterates
related to the Portuguese man-o'-war). When I lived in central California
in the early 70's, I frequently saw windrows of Velella cast up on the
beach. They are squishy and fishy at first, then dry crisp, like discarded
plastic wrappers. Normally, they live in the centers of the oceans,
drifting on the currents, but sometimes a crosswind would drive the pelagic
herds onto the shore, particularly during the winter, if I remember right.
I never found any Janthina with them.
 
What season of the year is the most likely for finding windrows of Janthina
on the beach? My finds were both in winter.
 
The irony of the Zapotec women squeezing Purpura snails for purple dye is
that the same molecule is obtainable as indigo (from the plant) and as
aniline dyes (from coal tar). Yes, the blue in your blue jeans is
chemically almost the same as the royal purple from Murex snails. Sorry, I
have no references on this. Anyone?
 
Andrew K. Rindsberg
Geological Survey of Alabama