Chaetognatha, also known as arrow worms, are a phylum of small, predatory marine invertebrates. They are characterized by their elongated, slender bodies and their retractable, chitinous spines, which they use for defense and to capture their prey. Chaetognatha are carnivorous and feed on small planktonic organisms, such as copepods and other small crustaceans. They have a simple digestive system and lack a true circulatory system, but have a well-developed nervous system and sense organs. Chaetognatha play an important role in marine food webs as predators, and their abundance and distribution is often used as an indicator of the health of marine ecosystems. Despite their importance, chaetognatha are often overlooked because of their small size and elusive nature.