Sea worms are marine invertebrates that belong to the phylum Annelida. They have long, segmented bodies and can be found in various ocean habitats, from sandy shores to deep-sea environments. There are many types of sea worms, including polychaetes, which are known for their bristle-like structures called setae that help them move and burrow. These creatures play an essential role in the marine ecosystem by breaking down organic matter and serving as a food source for various animals, such as fish and crustaceans. Sea worms contribute to nutrient cycling in the ocean, making them vital for maintaining healthy marine environments.