Final answer:
The hooks arrow worms have: some having two hooks and others having up to four on each side.
Step-by-step explanation:
Arrow worms, also known as Chaetognaths, have a unique structure called grasping spines that resemble hooks. These hooks are found on either side of their head and are used for capturing prey. The number of hooks can vary among different species of arrow worms. Some species have two hooks, while others can have up to four hooks on each side of their head.
These hooks play a crucial role in arrow worms' feeding behavior. When hunting, arrow worms use the hooks to grasp and immobilize their prey, which mainly consists of small zooplankton. By anchoring themselves onto the prey, arrow worms can inject enzymes to digest their food externally before consuming it.
In conclusion, the number of hooks found on arrow worms can differ depending on the species. However, it is common for arrow worms to have two to four hooks on each side of their head.