SOME LEFT-HANDED COILED SEA SHELLS

             

This post is # 560 in my continuing sequence of blog posts since I began my blog in 2014.

Nearly all gastropod (snail) sea shells are right-hand coiled (dextral), but there are a few species that have left-hand coiled (sinistral). The reason why seashells coil in a left-landed way (sinistral) is related to genetic processes. This blog post illustrates examples of each type of coiling. 

Figure 1. The shallow-marine seashell genus Busycon carica [the so-called “knobbed whelk”] lives in bays and offshore on the east coast of the United States. Most shells of this genus are dextral coiled, like the example shown here: when viewed with the apex of the shell upward, the aperture (opening) in the seashell is on the right. The shell illustrated here is about 17 cm (6.5 inches) in height.

Figure 2. Busycon perversum (the “lightning whelk”). I am not sure what the size of this specimen is, but the maximum height for this species is about 30 cm (13 inches). It lives in nearshore waters on the east coast of the United States. This shell is an example of a sinistral coiled shell. Image from North American Wildlife (1982, p. 246). 

Figure 3. The closely related gastropod Busycotypus canaliculata was introduced in 1938 in the San Francisco area. There is no certain information as to how or exactly when this species reached the west coast, but it possible that it was brought along with oysters or lobsters from other regions (Hanna, 1966, p. 49). The illustrated specimen shown here is dextrally coiled and 16 cm (6.5 inches) in length. This species, which has also been found from Orange County, southern California (L.T. Groves, personal commun.) can have a shell up to 8 inches in height. (Information and photograph kindly provided by Lindsey T. Groves, Collections Manager of Malacology, Los Angeles County, California).

SOME OTHER MARINE SINISTRAL GASTROPODS

Triphora shells, typically 2 to 10 mm in length, are also a sinistral gastropods. For an example, see one of my previous blogs (October 16, 2023).

There are two other extant marine gastropod genera that can have sinistral shells: 1) Sinistralia [in the family Fasciolariidae] and 2) Antiplanes [recently reclassified as being in family Pseudomelatomidae].

I also detected in the literature, two extinct marine gastropod genera that can have sinistral shells. These are the east coast (Virginian to Florida) Conus adersarius, of Plio- Pleistocene age, and also the northern Atlantic Neptunea angulata of Plio-Pleistocene age.

References

Abbott, R.T. and S. Peter Dance. 1982. Compendium of seashells. E.P. Dutton, New York, 410 pp.

Hanna, G D. 1966. Introduced mollusks of western North America. Occasional Papers of the Academy of Sciences, no. 48, 108 pp., 4 pls.

North American Wildlife: An illustrated guide to 2,000 plants and animals. Reader’s Digest, Pleasantville, New York. Editor S. J. Wernert, editor. 615 pp.

Wikipedia, 2026. 

WoRMS (https://marinespecies.org)

ACKNOWLEDGMENTS

Lindsey T. Groves, Collections Manager of Malacology, Los Angeles County, California.