Sand dollars

(I'm interested in finding out more about "sand dollars". I know what they look like what am curious to know what kind of shell? they are and what they look like alive. Can you perhaps tell me)

Sand Dollars are not really "shells" in the strict sense. The shells that most collectors collect are from a group of animals called molluscs (or mollusks), which includes clams, oysters, scallops, snails, conchs, octopus, and their relatives. Sand Dollars belong to an entirely different phylum of animals called echinoderms, which also includes sea urchins, starfishes, sea cucumbers and their relatives. A sand dollar you find on the beach may be either smooth white or slightly fuzzy brown. If it's brown, it is a fresh specimen and looks just as it did in life, and is covered with microscopic spines. If it is white the spines have fallen off after death and it has been bleached by the sun.
(Answer by M. Paul Monfils via the Forum)