Georgia's Official State Shell

Knobbed Whelk WIDTH=160 HEIGHT=160 ALIGN=

The Knobbed Whelk is both the mascot of the Georgia Shell Club and the official State Shell for Georgia. These pages present information on the biology, taxonomy and life history of the Knobbed Whelk, Busycon carica.

Taxonomy
Anatomy
Biology
Shell Characters
Life History
Relatives
References

Taxonomy

The Knobbed Whelk, Busycon carica was described by Gmelin in 1791. It is one of approximately fourteen recognized species (depending on how you fell about subspecies and forms) of the subfamily Bucyconinae, in the family Melongenidae. This subfamily has been a conspicuous component of the marine gastropod fauna of eastern North America through most of the Cenozoic. Whelks have flourished in this region of the Atlantic Ocean since the lower Miocene (approximately 30 million years ago). Today the Knobbed Whelk is a common predator of the intertidal mudflats, and can be found offshore to 26 fathoms.

Shell Character

juv & adult Busycon carica

The adult shell is large (up to 240 mm long) and thick with tubercles or spines on the shoulder. Juvenile shells have small beads on the shoulder of the shell that grow progressively larger to form tubercles or spines on larger shells. The shells coils dextrally (right-handed, or in a clock-wise direction) and have a long siphonal canal. The suture between whorls is simple. An adult shell will have 1+ protoconch and up to 8 additional whorls. The exterior color is grayish white to tan, often with darker brown axial streaks and a lighter band at mid-whirl. The axial streaks are more prominent in smaller specimens. The periostracum is fine and low, and often worn off larger shells. The interior of the shell can be any shade in the range between pale yellow - orange - dark deep red. Individual specimens shell shape, coloration and sculpture may vary widely.

Busycon carica shell

A form described by Montfort (1810) that has a yellow and brown interior, large spines and a tumidity around the siphonal canal is sometimes seen in the southern part of the species range. More often the individual characteristics Montfort attributed to this form (the tumidity and prominent spines) appear on shells that otherwise exhibit a normal carica's appearance. For this reason, the described form has never gained prominent use. In fact it seems that some of the characteristics he described, such as tumidity and prominent spines, actually change across the animal's range in a North-South cline.

Biology

Knobbed Whelk's currently inhabit the waters of the Atlantic from Cape Cod, Massachusetts to cape Canaveral Florida. Where they are often a conspicuous gastropod of the bays and estuaries. These animals begin life as small, ~4mm long, crawling snails. Each individual is either male or female, and reach maturity in 3 to 5 years. An adult female will be much larger than a male of the same age. Twice a year in the southern part of their range (April-May and September-October in Georgia) and once a year in the north, the snails gather in the estuaries to mate. After mating the female will remain to lay an egg case.

Adult females will deposit up to 100 fertilized eggs and nurse eggs into albumin filled egg capsules. The egg capsules are strung together in a long spiral string which is called an egg case or string. The total length of the string can reach over a foot and contain up to 160 capsules. The first capsules she produces will not contain any eggs (about 15) and are buried into the mud/sand as an anchor. The capsule material is secreated by the female, and molded into it's distinctive shape by her foot. The egg capsules of the Knobbed Whelk are coin-shaped, 20 to 30 mm in diameter and 3 to 6 mm thick with crenulations around the edges. The eggs are large (1 to 2 mm in diameter) and contain large amounts of yolk. They develop slowly, hatching in about 3 to 13 months. During development the embryos pass through larval stages and develop their first true shell with one post nuclear whorl.

Life History

Knobbed Whelks primarily feed on venerid bivalves. They will use their shell's lip to chip and pry the valves of their prey apart. Once there is sufficient room, they insert their proboscis and begin feeding. This method of feeding causes a significant amount of damage the shell, and may account for the limited growth of adult shells. Instead of growing, they must spend their time and energy repairing their shells. In intertidal waters, the snails are active throughout the day. Local populations often migrate offshore into deeper waters during the cold winter of the north, and the hot summer of the south.

Relatives

The Knobbed Whelk has several relatives, three of them can be found along the coast of Georgia: the Channeled Whelk, Busycotypus canaliculatus (Linné, 1758), the Pear Whelk, Busycotypus spiratum pyruloides (Say, 1822), and the Lightning Whelk, Busycon sinistrum Hollister, 1958.

The Channeled Whelk and Pear Whelk have thinner shells than the Knobbed Whelk. Other differences between these whelk's shells and the Knobbed Whelk's shell, is that they have channeled sutures between successive whorls and their periostracum (a thin brownish colored layer that covers the outside of the shell) is 'furry'. The egg case of the Channeled Whelk is not coin shapped like the other species mentioned here. The egg case of the Pear Whelk looks like a small version of the Lightning Whelk's egg case.

The Lightning Whelk looks almost like a mirror image of the Knobbed Whelk. Its shell is left-handed (coiling in a counter-clock-wise direction). There are a number of other differences between the Lightning Whelk and the Knobbed Whelk: the animal's body is black, not gray; and the shell's exterior has darker brown axial streaks, while the interior is white. However, Lightning Whelks do display a similar variety of shell shape and sculpture, and the egg case of the Lightning Whelk are very similar. The only major difference is that the Lightning Whelk's egg case is usually made up of larger egg capsules, and has tiny projections along the edges.

References
Clench, W. J. and R. D. Turner.
1956. The family Melongidae in the western Atlantic. Johnsonia 3(35): 161-188.
Conrad, T. A.
1853. Monograph of the genus Fulgur. Proceedings of the Philadelphia Academy of Natural Science. 6: 319.
Conrad, T. A.
1867. Synopsis of the genera Sycotypus, Browne, and Busycon, Botten. American Journal of Conchology. 3(2): 182-185.
DiCosimo, J.
1986. Biological review and commercial whelk fisheries analysis of Busycon carica, with comments on B. canaliculatum and B. contrarium. Virginia College of William and Mary, M.S. thesis. 125 p.
Edwards, A. L.
1988. Latitudinal clines in shell morphologies of Busycon carica (Gmelin, 1791). J. Shellfish Research 7(3): 461-466.
Edwards, A. L. and M. G. Harasewych
1988. Biology of the recent species of the superfamily Busyconinae. J. Shellfish Research 7(3): 467-472.
Edwards, A. L.
1985. Evidence for the conspecifisity of Busycon carica (Gmelin, 1791) and Busycon eliceans (Montfort, 1810). University of Georgia, M.S. thesis. 110 p.
Edwards, A. L. and C. M. Humphtey
1981. Electrophoretic and morphological survey of Busycon occurring in Wassaw Sound Georgia. Nautilus 95(3):144-150.
Emerson, W. K.
1953. A review of Mark's subgenera of Busycon Roding, together with remarks pertaining to the genus. Nautilus. 67(2): 61-66.
Gmelin, J.F.
1791. Systema Naturae, ed. 13, tome 1, pt. 6, p 3545, No. 67.
Harasewych, M. G.
1978. Biochemistry of the hatching process in Busycon. Univ. of Delaware, M.S. thesis. 52 p.
Harasewych, M. G.
1982. The evolution and Zoogeography of the subfamily Busyconinae (Gastropoda: Melongenidae). University of Delaware, PhD dissertation. 216 p.
Hollister, S. C.
1958. A review of the genus Busycon and its allies part I. Paleontolographica American IV(28): 59-126.
Magalhaes, H.
1948. An ecological study of snails of the genus Busycon, at Beaufort, N.C. Ecological Monographs 18: 377-409.
Montfort, D. de.
1810. Conchyliologie systematique, et classification methodique des coquilles. 2 vol. 502-504 pp. Paris.
Paine, R. T.
1962. Ecological diversification in sympatric gastropods of the genus Busycon. Evolution 16: 515-523.
Pulley, T.E.
1959. Busycon perversum (Linne) and some related species. Rice Institute Pamphlet 46: 70-89.
Ram, J. L., L. Ram and J. P. Davis.
1982. Hormonal control of reproduction in Busycon: II. Laying of egg-containing capsules caused by nervous system extracts and further characterization of the substance causing egg capsule laying. Biological Bulletin. 162(3): 360-370.
Smith, B.
1938. Busycon carica (Gmelin) as a genotype. Nautilus 52(1): 16-20.
Weinheimer, D. A.
1982. Aspects of the biology of Busycon carica (Gmelin, 1791) in waters off South Carolina with emphasis on reproductive periodicity. College of Charleston, M.S. thesis. 92 p.

Last updated January 15, 1997