MARINE ANIMALS THAT ARE POISONOUS TO EAT 105 



The number of toxic dinoflagellates in the water varies according 

 to the season of the year and the abundance of nutrient chemical 

 substances that are available in the water. It has been observed 

 over a period of time that the dangerous period of the year is during 

 the warm season, which varies somewhat, but, in most instances, is 

 from March to November. It is during the warm period of the year 

 that dinoflagellates multiply. The Alaskan butter clam, Saxidomus 

 giganteus (Deshayes), is somewhat of an exception to this rule, in 

 that dangerous toxicity levels may occur at almost any time of the 

 year. 



Localities in which paralytic shellfish poisoning has occurred 

 are: the Pacific coast of North America, from the Gulf of Cali- 

 fornia to Alaska ; New Brunswick and Nova Scotia, Canada ; along 

 the Coasts of Norway, England, Germany, Belgium, Netherlands, 

 France; South Africa, and New Zealand. 

 Species of Shellfish Most Commonly Involved in Human 



Poisonings : 



Common Cockle, Cardium edule Linnaeus (Fig. 62, Top Left). 

 Inhabits European Seas. 



White Mussel, Donax serra (Chemnitz) (Fig. 62, Top Right). 

 Inhabits South Africa. 



Solid Surf Clam, Spisula solidissima (Dillwyn) (Fig. 62, Lower 

 Left). Occurs from Labrador to North Carolina. 



Gaper or Summer Clam, Schizothaerus nuttalli (Conrad) (Fig. 

 62, Lower Right). Found from Prince William Sound, Alaska, 

 south to Scammons Lagoon, Baja California, and northern Japan. 



Soft-Shelled Clam, Mya arenaria Linnaeus (Fig. 63, Top Left). 

 Inhabits Britain, Scandinavia, Greenland, Atlantic coast of North 

 America, south to Carolina ; Alaska, south to Japan, and Vancouver, 

 British Columbia ; California and Oregon coasts. 



Common Mussel, Mytilus calif ornianus Conrad (Fig. 63, Top 

 Right) . Inhabits Unalaska, Aleutian Islands, eastward and south- 

 ward to Socorro Island. 



Bay Mussel, Mytilus edulis Linnaeus (Fig. 63, Lower Left). 

 Ranges from the Arctic Ocean to South Carolina, Alaska to Cape 

 San Lucas, Baja California; practically worldwide in temperate 

 waters. 



Northern Horse Mussel, Volsella modiolus (Linnaeus) (Fig. 63, 

 Lower Right) . Found along the Pacific Coast of America from the 

 Arctic Ocean to San Ignacio Lagoon, Baja California; circumboreal. 



Atlantic Jackknife, or Razor Clam, Ensis directus Conrad 

 (Fig. 64, Top). Ranges from the Gulf of St. Lawrence River to 

 Florida. 



