* Backbone: Seahorses have a vertebral column, also known as a spine, which is a series of interconnected bones that provides support and flexibility.
* Internal Skeleton: They have an internal skeleton made of bone, not cartilage, which gives them structural support.
* Bilateral Symmetry: Their body is symmetrical along a central axis, with a head, tail, and paired fins.
* Notochord: While it's not visible in adults, they have a notochord, a flexible rod that supports the body during embryonic development.
* Dorsal Nerve Cord: They have a dorsal hollow nerve cord, a tube of nerve tissue that runs along their back.
In addition to these defining features, seahorses also share common ancestry with other vertebrates, indicating their evolutionary connection. They belong to the class Actinopterygii, which includes most bony fish.
It's easy to forget that seahorses are fish because of their unique shape and lifestyle, but their internal structure and evolutionary history clearly place them within the vertebrate group.