Practice question

Chaetognatha represent distinctive phylum of transparent dart-shaped pelagic carnivores known as arrow worms owing to arrow-like streamlined body divided into head armed with grasping spines, trunk and tail with horizontal caudal fin enabling rapid darting swimming. Anterior head with eyes, corona and vestibular ridge. All marine predominantly holoplanktonic, important predators of copepods and fish larvae. Historically considered deuterostomes due to enterocoely, but molecular data place them within gnathiferan protostomes near rotifers. Coelomate with large cavities, direct development, ancient lineage dating to Cambrian fossils showing long evolutionary persistence and ecological importance in oceans.