  Yes, an oyster is a mollusk, a grouping with many various characteristics. Squid, clams, scallops, and starfish, etc. are also mollusks. They fit into the definition o … f invertebrates because they do not have a spine or backbone.    Additional interesting fact about oysters:   The oyster is usually ambisexual. It begins life as a male, then becomes a female, then changes back to being a male, then back to being female. A vertebrate i … s an animal that are a backbone, which affects its  body shape.   For example: we humans are vertebrates, so are cats, dogs, chimps,  elephants, etc...