Marine invertebrates are animals that live in the ocean and do not have a backbone. This diverse group includes creatures like jellyfish, octopuses, and sea urchins. They play essential roles in marine ecosystems, serving as food for many fish and helping to maintain the balance of ocean life. These animals come in various shapes and sizes, from tiny plankton to large squid. Marine invertebrates can be found in different habitats, such as coral reefs, deep-sea environments, and sandy shores. Their unique adaptations allow them to thrive in the ocean's many conditions, making them fascinating subjects of study.