A slender transparent worm-like animal with fins, having spines on the head for grasping prey. It is common in marine plankton.Also called chaetognath.
Phylum Chaetognatha.
Chaetognaths (commonly named arrow worms) are transparent marine metazoans, ranging in size from 2 to 120 mm....
As mentioned, the chaetognaths (‘arrow worms’) are clearly orthodox bilaterians.
Early Cambrian ‘protoconodonts’ are currently believed to be the unrelated remains of chaetognaths (or ‘arrow worms’).