Reference: Biol. Bull., 147: 321-332. (October, 1974) LARVAL DEVELOPMENT OF THE GIANT SCALLOP PLACOPECTEN MAGELLANICUS (GMELIN) * JOHN L. CULLINEY Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138 The giant sea-scallop, Placopecten magellanicus (Gmelin) ranges along the east coast of North America from Labrador to Cape Hatteras (Abbott, 1954). Although primarily a continental shelf species, it may be found one meter below low tide in the Gulf of Maine (Read, 1967). At the southern end of its range, off North Carolina, P. magellanicus generally occurs in water over 150 feet (46 meters) deep (Porter, 1974). A regional fishery for P. magellanicus, chiefly off New England and eastern Canada, has stimulated some research on the biology of this scallop including studies of length-weight relationships and gonad development (Haynes, 1966) ; thermal tolerances and acclimation (Dickie, 1958) ; and growth rates in different geographical regions (Stevenson and Dickie, 1954 and Merrill, Posgay and Nichy, 1966). Up to the present, however, research on the giant scallop has been confined to the adult stage. The dearth of information concerning larval biology of P. magellanicus has formed a conspicuous gap in knowledge of the life history of this species. The purpose of this paper is to describe the complete larval development of P. magellanicus, including observations on larval salinity tolerance and settling behavior. Information derived from rearing larvae in the laboratory may help to confirm the identification of P. magellanicus larvae from the plankton and will aid future mariculture efforts with this valuable food species. MATERIALS AND METHODS Sexually mature scallops were collected by SCUBA diving at Isles of Shoals, New Hampshire on September 21, 1973. They were placed in sea water in a styrofoam chest and held for 8 hours at approximately 5 C until returned to the laboratory. I selected small adults ( 3"-5" diameter) to minimize stresses to the animals from confinement in limited volumes of water both during transport and in subsequent spawning containers in the laboratory. Males and females were separated for spawning, which was stimulated therm-ally by raising the temperature 3-5 C. Gametes and developing larvae were generally handled as recommended by Loosanoff and Davis (1963) and Culliney, Boyle and Turner, ( 1974) . Larvae were reared in cylindrical glass jars containing two liters of sea water filtered to remove particles larger than one micron in size. The sea water was changed every two days. Salinity during development was nearly constant at 1 This research was supported by ONR Contract Number NOOO 14-67A-0298-0027 with Harvard University. 321
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