The green crab, scientifically known as Carcinus maenas, is a small, invasive species of crab native to the North Atlantic Ocean. It typically has a greenish color with a hard shell that can grow up to 4 inches wide. Green crabs are known for their adaptability and can thrive in various environments, including estuaries and coastal areas. These crabs are omnivorous, feeding on a wide range of organisms, including clams, oysters, and small fish. Their presence can significantly impact local ecosystems, often outcompeting native species for food and habitat. As a result, green crabs are considered a threat to marine biodiversity in regions where they have been introduced.