Vertebrata are a subphylum of Chordates. These, of course, have all the characteristics of any chordate, but have a number of other characteristics unique to their group. These additional traits include the presence of a braincase and a tripartite brain, with cranial nerves. During development the ectoderm pinches off to form the neural crest and cells migrate throughout the body to form a variety of structures. These have the ability to form teeth, pigment cells, bone, muscles and more. Rather than simple filter feeding, muscles now control the action of taking in water for both breathing and feeding. Likewise, muscles now control the digestive tract and move the nutrients along through peristalsis. The pituitary gland has been split into both adenohypophyis and neurohypophysis hormonal control. Furthermore, the optic tectum is present in vertebrates, providing better visual information processing.
A specific class of Vertebrata is called the Cyclostomata, which may be further divided into Myxinoidea, the hagfish, and Petromyzontida, lampreys. Hagfish have no bones and their skeleton is mostly made of cartilage. However, they do have vestiges of a hemal spine, ventral to their notochord. While they do not have true eyes, they do have eyespots used to detect light. Hagfish have a single nostril on the top of their head and a single semicircular ear canal. Their skin is covered in a number of mucus pores, which produce large amounts of mucus and slime when the fish is agitated. These fish are mainly considered scavengers, though may be known to eat smaller marine worms. Their mouths contain keratinized teeth which they use to pierce prey with and burrow inside or by sucking the nutrients out.
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