chaetognath

Chaetognaths, commonly known as arrow worms, are a phylum of marine invertebrates. They are small, predatory organisms that inhabit all oceans of the world, from the surface to the deep sea. Their bodies are typically elongated and transparent, resembling small arrows, which gives them their common name. A key characteristic of chaetognaths is the presence of chitinous spines, or "bristles" (from which their phylum name is derived, meaning "bristle jaw"), located around their mouths, which they use to grasp prey.

These creatures are an important part of the marine food web, feeding on planktonic crustaceans, other chaetognaths, and small fish larvae. In turn, they are preyed upon by larger marine animals, including fish and squid. Chaetognaths play a role in the biological pump, contributing to the transport of carbon from the surface to the deep ocean. Their distribution and abundance can serve as indicators of oceanographic conditions.

Reproductively, chaetognaths are hermaphroditic, possessing both male and female reproductive organs, although they typically cross-fertilize. They are bilaterally symmetrical and possess a coelom. Despite their relatively simple body plan, they have a complex nervous system and well-developed sensory organs. Their evolutionary relationships have been a subject of debate among scientists, with ongoing research attempting to clarify their position within the animal kingdom.