top of page


About Shells
Shell anatomy, terminology, classification, nomenclature, etc.

Feb 4, 2010 Harry Lee posted:

"Here is the reference for the whorl-counting method cited by Marlo:

Verduin, A., 1977. On a remarkable dimorphism of the apices of sympatric closely-related marine gastropod species. Basteria 41(5-6): 91-95. Dec. 20."

2/5/2010 José H. Leal, Ph.D., Director and Curator The Bailey-Matthews Shell Museum, wrote:

"Many authors working with large numbers of specimens and species of marine and fossil gastropods do count the nucleus. Look in Hansen (1980), Jablonski & Lutz (1980; 1983), Maes (1983), Shuto (1974), Taylor (1975), and Leal (1991), to cite a few. Using their methodology, the starting line in Verduin's drawing (the "zero" line) would be tallied already as 0.5 whorl.

That being said, I believe that, no matter the methodology used, it is important that it should be clearly defined. Anyone can then translate the work in question into their preferred system.

Hansen, T. 1980. Influence of larval dispersal and geographic distribution on species longevity in neogastropods. Paleobiology 6: 193-207.

Jablonski, D. & R.A. Lutz. 1980. Molluscan larval shell morphology - ecological and paleontological applications. In: D.C. Rhoads & R.A. Lutz
(eds.) Skeletal Growth of Aquatic Organisms. Plenum Press, New York, pp.

Jablonski, D. & R.A. Lutz. 1983. Larval ecology of marine benthic invertebrates. Biological Reviews 58: 21-89.

Leal, J.H. 1991. Marine prosobranch gastropods from oceanic islands off Brazil; species composition and biogeography. Universal Book Services, Oeestgest, The Netherlands, 418 pp.

Maes, V.O. 1983. Observations on the systematics and biology of a turrid assemblage in the British Virgin Islands. Bulletin of Marine Science 33:

Shuto, T. 1974. Larval ecology of prosobranch gastropods and its bearing on biogeography and paleontology. Lethaia 7: 239-256.

Taylor, J.B. 1975. Planktonic prosobranch veligers of Kaneohe Bay, 606 pp.
Unpublished PhD dissertation, University of Hawaii."

Harry Lee, author of Marine Shells of Northeast Florida (2009) commented:

"Dear Marlo, José, and other quizzical whorl-counters,

Well before any of the cited (marine) authorities, Pilsbry (1939: xi) introduced a system* which produced whorl counts exactly half-way between those of Verduin (1977: 92) and José's adopted method.

Perhaps there's a bit of irony in Marlo, who keeps no secret of his disinterest in land snails, casting his lot with Pilsbry, whose methods seems to be otherwise practiced almost exclusively by "terrestrial" malacologists.

After saying all that, I'll admit I certainly agree with José on the matter of defining one's methods.

Pilsbry, H.A., 1939. Land Mollusca of North America north of Mexico vol 1 part 1. Academy of Natural Sciences, Philadelphia. xvii + pp 1-573 + ix. Dec. 6.
Verduin, A., 1977. On a remarkable dimorphism of the apices of sympatric closely-related marine gastropod species. Basteria 41(5-6): 91-95. Dec. 20."

*Harry wrote in a prior email, "Pilsbry (1939-1948) used the method [pictured below] which yields 0.25 whorls more that the Verduin technique. Land snail people generally use this method."


2/6/2010 Charlie Sturm, Research Associate - Section of Mollusks Carnegie Museum of Natural History, added:

"I believe that Juan Jose parodiz also published on this question, He dealt with this topic in the following publications:

Parodiz, J.J. 1951a. Me´todos de conquiliometrý´a. Physis
20(58): 241–248.
Parodiz, J.J. 1973e. Gastropod conchometry. Pittsburgh Shell Club Bulletin 8: 14–16."

AYDIN ÖRSTAN commented:

"There is no correct way. Like Jose said, you just have to explain how you did it. I always count along the suture: at the starting line of Verduin, there is already 1 complete revolution, or 1 whorl. If you are consistent, in the final tally suture counting will always give a half a whorl more than the "Verduin method" (he wasn't the one who originated it).

If you don't care about the total number of whorls, but only care about the whorl numbers with respect to the aperture, then you can count them starting at the aperture. The body whorl is 1, the penultimate whorl is 2, so on.
This is useful if you are working with tall shells. See my paper: Örstan, A.
1999. Drill holes in land snail shells from western Turkey. Schriften zur Malakozoologie 13:31-36."

Roland Houart, author of The Trophoninae (Gastropoda: Muricidae) of the New Caledonia region (1995), was direct in expressing exatly my sentiments:

"For those having my papers, maybe it is nice to know that I always include the nucleus in the count of the protoconch whorls in Muricidae. Anyway I don't see why it should not be included."

bottom of page