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Georgia  State Symbols, Sea Shell

Knobbed Whelk

(Busycon carica gmelin)

Adopted in 1997.

The knobbed whelk is a whorled shell, eight inches long at maturity, displaying heavy spines, many knobs, and an orange or red mouth. Minerals in Georgia coastal waters cause ocher striations on the sand-colored, semi-gloss surface. This marine snail shell is found all along Georgia's shoreline, out to 30 feet of water.
 

 See Georgia and New Jersey

  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

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.



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
 

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