Something about Seashells
by Dr. Ray McAllister
At a soiree some years ago, I had the pleasure of meeting R. Tucker Abbott, recently deceased, who is known to most of you as the author of a series of beautifully illustrated books about seashells. After the meeting we repaired to his hotel where I picked his brain about sea shells for about 2 Ĺ hours, while all the ladies except Sue Fish talked woman talk. Sue and I queried him about everything we always wanted to know about mollusks, but didnít have anyone to ask. Let me regale you with a few of the tidbits we learned.
Have you ever heard that the Chinese manufacture valuable wentletrap shells out of rice flour, so skillfully that most people, even conchologists (shell specialists), cannot tell by looking at them that they are synthetic! Well Tucker says it ain't so. Just a good story that crops up every so often.
And how about the shells that coil clockwise in the Northern Hemisphere and counterclockwise south of the Equator? Joseph Conrad (I believe) says so in one of his books, and it is widely believed. Again, it isnít so!
While Coriolis Force operates on all moving things, including seashells as they grow, the term in the Coriolis Equation for velocity is so small for growing shells, that natural forces and genetic determinants make them coil the way their genes say. There are some clockwise coiling shells and some that coil counterclockwise, but few that coil both ways and none that he knows of that are directed by the location north or south of the Equator.
Rarely a shell that should normally coil in one direction will be discovered coiling in the wrong direction. Such shells are extremely valuable to a collector, but it will do no good to take larval shells to Australia to get opposite coiling. It doesnít work.
Tucker also told us the name of the most valuable shell in the world, but I've forgotten it. I'd always thought it was the Glory of the Seas Cone shell (Conus gloriamaris), but it isn't, at least not any more. Years ago, only a very few of these shells were known and each was worth a small fortune. Then more and more showed up and the price dropped. Natives of the Indo-Pacific region, who fish for shells for the souvenir and collectors markets, found that they could catch the Glory of the Seas Cone by spreading a fine mesh net on the bottom with bait in the center. The snails crawl up on the net, get their foot caught in the mesh and are captured. By the way, foot is the proper term for the part of a snail that carries the shell along! Thatís why the scientific name pelecypod, for hatchet foot!
I asked him if our Atlantic cone shells were poisonous. I've caught Crown Cones in Florida and handled them very carefully. He said that all cone shells are poisonous; some much more than others. There are several in the Pacific that are so deadly that they can kill a strong man!! Fortunately our Atlantic cones are not so bad.
Several cases of stings by Crown Cones and other Atlantic cones have been described. They apparently feel like a bad bee sting. The stinger is one of the many possible modification of the snails foot. Some snails use a radula (file like part of the foot) to rasp holes in other snail shells, or in sea biscuits, so they can eat the insides. Others modify the radula into a harpoon like stinger. Ah, the wonders of my ocean!
Interestingly enough, long ago I spent some time on Johnson Island, in the north central Pacific. Our main recreations were diving, and watching the MATS planes that landed on our airstrip, to get a glimpse of a real live female stewardess. One day a boat pulled up to our dock as we were washing our dive gear, and a young man held up a cone shell about 6 inches long. Look at this beauty, he said. I looked and immediately knocked it from his hand and into the water. Good god, man, I said, donít you know that cone shells may be deadly? Read R. Tucker Abbottís books about shells sometime! He was livid, and said Tucker Abbott is my uncle. But he had not read the books and did not know the cones were poisonous. When I dove down and carefully retrieved the shell, it was dead and there was nobody home. He hadnít known it, though, and could have died for his ignorance as is reported for a football player from Hawaii, who lasted almost two hours after being stung by a beautiful cone.
How does a spiny oyster (Spondylus americanus) build its long curved spines? And for that matter, the same question might be asked for many other similarly ornamented shells. Well, Tucker says there are shell secreting cells in the mantle of the spiny oyster (which is really a kind of scallop). When the animal decides to enlarge its home, these cells deposit a layer of calcium carbonate around the edge of the shell and make it bigger. Periodically it sticks a finger of mantle and shell secreting cells up into the water for two or three inches and starts to make new shell around this fleshy protuberance. As it deposits carbonate, the fleshy part slowly withdraws into the shell leaving a long beautiful spine behind.
I was glad to know this because I've wondered about it ever since I found my first spiny oyster in about 120 feet of water off SE Florida. He also said there is only one species of Spondylus locally. When it grows on a reef, the spines are usually poorly developed and the shell is more massive. Perhaps reef critters bump the fleshy spikes and they withdraw without completing the spines. On the sand and rubble flats in deeper water, the spinys grow long beautiful spines that make them worth $25 or more to the collectors and tourists..
Very often one find the spiny oysters growing on a small fragment of shell or coral in the deep water. They commonly are coated with an encrusting sponge which is quite distinctive. I look for the sponges to find the spinys, but only take one or two a year, so as not to rape the reef. Tucker tells of the Venus Cone, which has long thin spines situated in such a way as to form a cage around the foot. As the cone wanders along the bottom, the shell is held high by the extended foot, but if attacked, lowers the shell quickly so that the cage protects the vulnerable soft foot. Id often wondered what purpose such extreme ornamentation served.
Tucker did not say this, but I suspect the long spines on the spiny oyster and the Venus Cone, for example, may deter another mollusk, the octopus, from eating them. We learned a great deal more from Tucker Abbott, but there is a limit to what you can absorb in one sitting, so Ill save more stories for another time, or, better yet, get one of the R. Tucker Abbott shell books and learn for yourselves.