180 U. S. BUREAU OF FISHERIES 



From the swimming embryo an even more activeh^ .swimming; larva 

 develops, eventually with a somewhat clamlike bivalve shell (the 

 larval or prodissoconch shell) and a hi<jhly developed swimming 

 organ, the velum. Although different organs are involved, feeding 

 is essentially like that of adults. 



The succeeding stage corresponds to the earl}^ " spat " or '^ set " 

 stage of the oyster. However, the scallop is smaller than the oyster 

 during this period of development and is not permanently attached 

 but able to crawl, swim (in the manner of the adult), and float on 

 the surface film with foot extended. By means of the byssal gland 

 in the foot, it is able to attach itself by threads (the b^^ssus) to eel 

 grass or other objects. It can break and remake the byssus at will. 

 During this period simple gills, a few eyes, and a shell more like that 

 of the adult, with long, straight hinge but without the ribs, are de- 

 veloped. Ribs appear and the adult shell begins to form when the 

 animal is aboiit one tAventy-fifth of an inch (1 millimeter) in diame- 

 ter. Gills beconle more complex, eyes more numerous. The foot 

 becomes relatively small and insufficient for locomotion but retains 

 the byssal gland and, to a late stage, the ability to secret a byssus. 



GROWTH 



Among economic bivalves the scallop is remarkable for its rapid 

 growth. Marketable size is attained in a year or even less. In the 

 more favorable areas a diameter of 3 inches may be attained in a 

 year. Nearly all of the commercial crop consists of scallops from a 

 year to 20 months old. • 



LENGTH OF LIFE 



The bay scallop is decidedly a short-lived form, but the full, 

 natural length of life in North Carolina is not known definitely. 

 Doctor Belding," working in Massachusetts, found the limit to be 30' 

 months, and that very few live to be 2 years old. Under present 

 conditions few live to be 2 year,s old in North Carolina. However, 

 that means little, for nearly all are caught by the time they are 18 or 

 20 months old. A few scallops live to be 2 years or more old. Ex- 

 treme destruction of adult scallops by scallop fishermen makes it 

 difficult to tell what proportion would survive if spared by man. 

 There is some indication that a considerable proportion Avould 

 survive to be 2 or nearly 2 years of age. 



ENEMIES AND DESTRUCTIVE AGENCIES 



The ])rincipal natural enemy of the scallop seems to be the star- 

 fish. The scallop falls a comparatively easy prey to this persistent 

 predacean. Protection for the scallop lies in its power of perception 

 and locomotion. The starfish annually destroys large numbers of 

 scallops in North Carolina but is not known to be a menace in any 

 locality. 



'A Report upon the Scallop Fishery of Massachusetts, by D. L. Belding. Boston, 1910, 



