Cephalopodcast - The Ocean Podcast

I am starting another new feature here on the Cephaloblog, one that I hope will become a regular edition. I am calling it, What the Shell is That?

My inspiration comes from the weekly blog arcs of folks like PZ Myers (Friday Cephalopod), Peter and Craig (Friday Deep-Sea Picture), Rick MacPherson (Monday Moray) and Martin Brummell (Friday Fish), to name just a few.

The focus of What the Shell will be on things I find at the beach. Living on the southwest coast of Florida, that means mostly molluscs, especially bivalve (clam) and gastropod (snail) shells. But it could also be skate eggs, algae or nurdles. Anything in the intertidal is fair game, and not just dead things on the beach either.

Note, I am not a professional malacologist or a competent conchologist. Just a curious beachcomber looking to get outside more to search the surf and share with you. I am not interested in collecting live shells, just taking pictures and leaving only footprints/bubbles. I hope to post one entry each weekend, the day depending on when I can hit the beach.

Florida Horse Conch (Triplofusus gigantea)

The official state shell of Florida is neither a horse (obviously) nor a true conch (not so obviously) nor is it limited to just Florida. True conchs are in the family Strombidae, but horse conchs, along with the tulip shells, are in the spindle shell family Fasciolariidae. Up until recently this particular animal was known as Pleuroploca gigantea. I am still not certain what prompted the change in taxonomy.

I suspect it is called a horse conch because it is the largest snail in North America. These animals grow up to two feet long and are voracious predators of other marine snails.

The individual pictured above was a juvenile, approximately 3 inches long (7.5 cm) found half-way in the water on a piece of drift wood.

Some questions I am still seeking the answers to:

• Why is the horse conch orange? How does it get this distinctive color.
• As an adult, why does it have such a flakey periostracum?
• Why is the horse conch so large?
• Why the change from Pleuroploca to Triplofusus?

References

• Rehder, Harald and James Carmichael. The Audubon Society Field Guide to North American Seashells. New York: Knopf, 1981. pp. 575.
• Ruppert, Edward and Richard Fox. Seashore Animals of the Southeast. Columbia: University of South Carolina Press, 1988. 116.
• Williams, Winston. Florida’s Fabulous Seashells. City: World Publications (Tampa, FL), 1988. pp. 54-55
• Witherington, E., Blair and Dawn Witherington. Florida’s Living Beaches. City: Pineapple Press (FL), 2007. pp. 73.

Additional Links

• More photos: What The Shell
• Whitney Laboratory of Marine Bioscience: Horse Conch (Pleuroploca gigantea)
• Spindle Shells, Scallops, an excerpt from Florida’s Seashells by Blair & Dawn Witherington (pdf)

UPDATE: bobsonguam now informs me that Pleuroploca papillosa is being considered.