This is a follow-up to Reggie’s post on the perfect giant tun shell that he found on the beach. When he found it, the actual dead snail came out of the shell and landed on the sand, releasing an incredibly foul odor. 
After Ted found the second one, I came home and looked through all my shell and mollusk guides to see what I could find out about the actual snail. What did it eat? Who were its main predators? Where and how did it live? die?
I found out some pretty interesting facts: The giant Tun, Tonna Galea, is a deep-water (10-30m) snail which feeds on sea stars and sea cucumbers. The foul stench may be due to the fact that its saliva can be 2-4% sulfuric acid, which helps it bore into echinoderms and other mollusks. The population has suffered in the past because of poaching from shell collectors. It lives in Atlantic, Caribbean, and Mediterranean waters, and extends as far north as North Carolina. I’ve never found a whole one on Dewees before, but did find a small one on Bull Island a few years ago.
The beach was the usual treasure trove of discovery, and these shells were found with a number of dead sea stars, so whatever killed the sea stars might have exacted a toll among ton shells as well. In addition, there were many spent egg cases for whelks. After only finding small fragments of Tun shells now and then, we found two intact ones and countless other fragments this time.
In my web searching, I found an interesting youtube film of one walking on the ocean floor. It is almost 7 minutes long, so I recommend waiting for it to buffer and then clicking through quickly. The reason it’s so long is that the Tonna Galea falls off a small cliff, and we watch to see if it can right itself. (Yes, a cliffhanger!)
THEN, I was looking back at my photos, and began wondering about the egg case for the Tun shell. When I searched for Tonna Galea egg case, I came upon a photo of Tonna Galea laying down an egg rosette. Eureka!!! It is the Giant Tun that created our mystery object from our earlier post! Our mystery is solved! I can understand why it is called an egg rosette. These rosettes were the mystery item we couldn’t identify on the beach in October.
Good detective work Judy! You KNEW it wasn’t a moon snail all along 🙂
So envious you found such a great shell on Dewees! Was there a big storm/lots of wind recently?
We have been very lucky, we have found 4 Giant Tuns in the last 4 months on the barrier islands we explored from Charleston to Georgetown. The last 2 have been fairly large. A little bigger than fist size. Happy shelling.
Hey Jim! Congratulations on the successful shelling this winter. I’ve talked to several other people from Dewees who found Giant Tuns this winter. Our theory is that the “cold shock” at the turn of the year was especially hard on the animals. A cold shock is when the water temperature changes dramatically in a short period of time. We saw its effects on other critters this winter, including sea stars (which some people call starfish) and urchins.
Dewees has a rule that people should only take 3 shells off the beach on a given day. That leaves plenty behind for other people, sand creation, and homes for hermit crabs and other creatures. It also forces you to decide which are your very best shells. I hope other people follow the same idea.
I am a diver who summers on the island of Patmos Greece. I have a very large collection of these Tun shells. When I saw the photo of the egg casing I wanted to shout….”put it back in the water”. I don’t take anything alive out of the sea. Love your website and your curiosity about nature. Email me if you would like to see some of my photos.
Thanks for your post! We agree about not taking anything out of the water… one of the reasons the egg casing was hard to identify is that we left it where we found it, and only had the photo to go on. Dewees Island has a pretty strong conseration ethic… we even ask people to limit their shelling to three treasures! Occasionally we gather live specimens from the tidepools to use in our touch tank, but we release them after using them to teach others about the infinite beauty and intricate relationships of the ecosystem.