Final answer:
Arrow worms, or chaetognaths, have lateral fins that extend along the sides of their body. These fins are used for stabilizing and maneuvering while swimming.
Step-by-step explanation:
Arrow worms, also known as chaetognaths, have a unique type of fin called lateral fins. These fins are long and slender and extend along the sides of the body. They are used for stabilizing and maneuvering while swimming. The arrangement and shape of the lateral fins vary among different species of arrow worms.