The Registry of World Record Size Shells is a conchological work listing the largest (and in some cases smallest) verified shell specimens of various marine molluscan taxa.

A successor to the Lost Operculum Club List of Champions (1950–1987) and World Size Records (1964–1990), it has been published on a semi-regular basis since 1997, changing ownership and publisher a number of times. Originally planned for release every two years, new editions are now published annually. Since 2008 the entire registry has been available online in the form of a searchable database. The registry is continuously expanded and now contains more than 52,000 listings and 93,000 supporting images.Registry of World Record Size Shells. wrs-shells.com.

Background World record size shells—commonly indicated by the acronym 'WRS'—are of broad interest to shell collectors and conchologists. In particular, those of species in the most popular families (such as cones or cowries) are often much sought after, and can thus command high prices.Whitehead, T. (June 1981). "World record size": why — and how . Hawaiian Shell News 29(6): 11.Jones, R.H. (June 1981). Do we keep track? Hawaiian Shell News 29(6): 11.Boone, C.E. (October 1979). Texas whopper. Texas Conchologist 16(1): 1–4.Trego, K. (10 March 2005). A record size for Megastraea turbanica (Dall, 1910) (Gastropoda: Turbinidae). The Festivus 37(3): 36.Weaver, C. (July 2010). Hawaii's giant marine univalves . Internet Hawaiian Shell News. [Originally published in Hawaiian Shell News, March 1965.]Owen, B. (N.d.) "World record" specimens of Haliotis species of the west coast of North America - a brief description and photo study. Of Sea and Shore. Collections of such shells are exhibited at a number of specialist museums, notably the Bailey-Matthews National Shell Museum (of which R. Tucker Abbott was the Founding Director), which has a dedicated "World Record Size Shells" exhibit.Brickley, J. (19 January 2011). Shell Museum debuts exhibit of world record-holders. Captiva Sanibel.Hoover, K. (28 January 2011). Shell Museum Unveils New Exhibit of Record-Size Shells. Ocean's Reach. The Bailey-Matthews National Shell Museum (13 January 2011 – 2 April 2012). World Record Size Shells 2012. Facebook.Bickel, M.H. (13 February 2023). Sanibel's Bailey-Matthews shell museum acquires world record-sized shell. Fort Myers News-Press.Leal, J.H. (17 February 2023). A Big World Record Size Shell! Bailey-Matthews National Shell Museum. Since volume scales with the cube of length, apparently small differences in stated size—in terms of greatest measurable dimension, usually given in mm—can correspond to dramatic differences in the visual appearance of size, something that is often underappreciated by novice collectors.Poppe, G.T. & J.R. Senders (1994). An Annotated Price Catalogue of Marine Shells. L'Informatore Piceno, Ancona.

Maximum and minimum sizes are also of interest to malacologists, and may be useful in delimiting closely related species. As an extensive compilation of maximum shell sizes, the registry has found use as a data source for scientific studies.Yong, E. (13 January 2015). How Big Are The Biggest Squid, Whales, Sharks, Jellyfish? Phenomena: Not Exactly Rocket Science.

Overview Scope Throughout its history the registry has covered four classes of molluscs: bivalves, cephalopods, gastropods, and scaphopods. Chitons have been excluded because their shells are formed from eight articulated plates and therefore the size of a fixed specimen depends in large part on the preservation method used.WRS Rules. wrs-shells.com.

Smallest adult sizes have been listed beginning with a few specimens of Cypraeidae and Strombidae in the first edition, and they now additionally encompass a third family: Marginellidae. Separate records for sinistral (left-handed) shells and obviously rostrate cowries (family Cypraeidae) are also included. Terrestrial and freshwater species, as well as fossils (of extant taxa or otherwise), are not covered by the registry.

Content

The bulk of the publication—which apart from the cover is unillustrated—comprises a list of taxa and their corresponding world record sizes. Each specimen in the registry is listed alphabetically under its recognised scientific name. This is usually a binomen (species name), but subspecies, varieties and forms are also included (the latter two are used informally and are not regulated by the ICZN). In addition to the shell size, each specimen is listed with its location, owner or repository, and the year it was collected, acquired, or registered (whichever is known, listed in decreasing order of preference).

Each print edition has an appendix with an alphabetical listing of entry totals for all private collectors and repositories having ownership of specimens in the registry. In the first edition, the most individual entries belonged to Victor Dan, with 369, closely followed by co-author Don Pisor on 325. This title subsequently went to Tennessee physician and world-renowned collector Pete Stimpson, who for a time held over 2,000 entries in the registry,Hursh, K. (30 May 2012). Headout: Show and Shell. Willamette Week. McRary, A. (6 June 2010). McClung displays record-setting shell collection. Knoxville News Sentinel. and whose WRS specimens have been exhibited at museums including the McClung Museum of Natural History and Culture.Shells: Gems of the Sea. McClung Museum of Natural History & Culture. As of the fifth print edition from 2008, the distinction of having the most WRS entries belonged to Havelet Marine, with 3,244 specimens, compared to Stimpson's 1,963.

Measurements The registry's rules specify that specimens "should be measured with vernier type calipers and should reflect the greatest measurable dimension of the shell in any direction including any processes of hard shell material produced by the animal (i.e. spines, wings, keels, siphonal canals, etc.) and not including attachments, barnacles, coralline algae, or any other encrusting organisms. Long, hair-like periostracum is not to be included." This "greatest measurable dimension" can be at odds with the standard scientific definition of shell length (from base to apex along the central axis for gastropods, and from the umbo to the ventral margin in bivalves).Vollero, S. (13 April 2000). Minutes of the San Diego Shell Club Meeting - March 16, 2000. The Festivus 32(4): 36.

Shell sizes are given in millimetres and recorded to the nearest , as is standard in conchology. To account for human error and environmental effects, new records are only accepted if they exceed the standing record by at least . This 0.3 mm margin also applies to smallest adult sizes exceeding .

Entries for specimens that tie the standing record can also be submitted. Though not included in the registry, they are kept on file for future use in the event that the current record holder is shown to be misidentified or smaller than originally claimed.

Superlative species

The three largest species in the registry are the bivalves Kuphus polythalamia, Tridacna gigas and Pinna nobilis, with maximum recorded shell sizes of , and , respectively. The fourth largest species, and the largest of all gastropods, is Syrinx aruanus with a maximum length of .Poppe, G. (25 June 2006). Re: LARGE SHELLS. CONCH-L archives. Eichhorst, T. (21 June 2006). Re: LARGE SHELLS . CONCH-L archives. Największe muszle morskie – rekordy wielkości. Concha. There are literature records of an even larger S. aruanus specimen measuring ,[Anonymous] (July 1982). This may be the world's biggest. Hawaiian Shell News 30(7): 12. Taylor, J.D. & E.A. Glover (2003). Food of giants – field observations on the diet of Syrinx aruanus (Linnaeus, 1758) (Turbinellidae) the largest living gastropod. In: F.E. Wells, D.I. Walker & D.S. Jones (eds.) The Marine Flora and Fauna of Dampier, Western Australia. Western Australian Museum, Perth. pp. 217–223. McClain, C. (5 May 2014). Sleuthing the Largest Snail. Deep Sea News. but these are erroneous and actually refer to the same specimen, which is on display at the Houston Museum of Natural Science.McClain, C.R., M.A. Balk, M.C. Benfield, T.A. Branch, C. Chen, J. Cosgrove, A.D.M. Dove, L.C. Gaskins, R.R. Helm, F.G. Hochberg, F.B. Lee, A. Marshall, S.E. McMurray, C. Schanche, S.N. Stone & A.D. Thaler (13 January 2015). Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ 3: e715. McClain, C. (12 January 2015). Sleuthing the Largest Snail . Deep Sea News. The extinct gastropod Campanile giganteum reached a similar or slightly greater size,Jung, P. (December 1987). Giant gastropods of the genus Campanile from the Caribbean Eocene. Eclogae Geologicae Helvetiae 80(3): 889–896. while the largest extinct bivalves and especially the largest extinct shelled cephalopods were much larger still (and the internal shells of the largest extant squid species also reach much greater lengths, as they approximate the mantle length). However, only external shells (with some exceptions, e.g. Spirula spirula) of extant species are covered by the registry. The largest listed cephalopod "shell" is that of Argonauta argo, at , though this is technically an eggcase rather than a true molluscan shell.