MISCELLANEOUS SHELLFISH INDUSTRIES 



667 



The common shallow-water scallop, found from Massachusetts to the Gulf of 

 Mexico, is the most important commercial species. This scallop is ordinarily desig- 

 nated as Pecten gibbus, var. borealis (Say) although it is also called Pecten 

 irradmns. In England it is called "fan shells," "frills," "queens," and "squims." The 

 giant deep-water scallop, found from New Jersey to Labrador, is Placopecten 

 grandis (Solander). 



Several species of scallops are found on the Pacific Coast, but the western 

 scallops are not utiUzed commercially to any considerable extent. 



Fig. 32-1. The bay scallop 

 ( Pecten irradians ) . 



^Courtesy U. S. Fish and Wildlife 

 Service) 



Placopecten grandis has a bathymetrical range from 1 to 150 fathoms. Because 

 of the depth at which this shellfish lives, comparatively httle is known about its 

 habits. It possesses a much larger, smoother shell than Pecten gibbus and is, there- 

 fore, called "giant scallop" or "smooth scallop." It is also called, from the habitat, 

 "sea scallop." The foot is relatively small, and is split at the end; it possesses a 

 large byssal gland. The sexes are separate. The embryos pass through a free- 

 swimming stage, after which they settle to the bottom and attach themselves to 

 some object by means of a byssal thread in much the same manner as do the 

 embryonic Pecten gibbus. The average length has not been determined; but this 

 scallop, like the shallow-water scallop, seldom lives over 2 years. 



Until recently comparatively little was known about the life history of this 

 scallop. Unlike the giant scallop in which the sexes are separate, Pecten gibbus is 

 hermaphroditic. The spermatozoa and ova are usually discharged alternately so 

 that there is httle danger of self-fertilization. Fifteen to 20 hours after fertilization 

 the eggs become a swimming embryo. The movements of its cilia keep it from 

 sinking to the bottom and cause it to rotate rapidly. A thin transparent shell 

 secreted by the shell gland grows over the young scallop before it is 40 hours 

 old. The young scallop does not take on the characteristics of the adult until 5 or 

 6 days after it has reached the veliger (swimming) state. During the last 3 days 

 of the swimming state a foot, which aids in swimming, begins to develop on the 



