Walk along almost any canal in the metro Phoenix area and you're sure to find thousands of shells each smaller than a quarter. What are they and how did they get there? 
Those are the questions reporter John D'Anna wonders about every time he walks his dog George along the neighborhood canal path. This week, Valley 101 is answering them. 
The shells' official name is Corbicula fluminea, but they're more commonly referred to as Asiatic clams. They were first spotted in the U.S. in 1938, then in Phoenix in 1956.