Fish are by far the most diverse group of vertebrates with more species than all other groups of vertebrates combined. Now we said that the evolution of jaws was a very important step, but before we had jawed fish, we had jawless fish, and jawless fish actually lack a backbone, but they have cartilage vertebrae. We're going to look at 2 types of agnathans fish, which are also called cyclostomes, which basically means, like, circle mouth. You'll see why in a second, though much to your chagrin. And the first organism we're going to look at is the hagfish. This is maybe one of nature's grossest animals. These are scavengers that actually swim like snakes, and the reason they're so gross is see all these little dots along the hagfish? Well, they actually secrete this water-absorbing preslime material. And basically, that preslime, as it's secreted from those glands along the body, sucks up the water around the hagfish and turns into this gross mucus-like kind of slime, substance. This is useful. It allows the hagfish to, you know, escape if a predator is going after it or something, but it is also the reason that hagfish are horrifying and disgusting, as we can see right here.
Now lampreys, arguably worse than hagfish. I don't know. This is tough. Both of these guys are kind of, well, they're no one's favorite animal, let me put it that way. Lampreys are parasites with that characteristic circular mouth, except theirs is filled with these horrible teeth that they use to feed on their hosts. They have a cartilage skeleton similar to how hagfish have cartilage vertebrae. Though it should be noted that their cartilage is actually not made from collagen. Lamprey cartilage is not made from collagen, which is one of the main components in most cartilage we see in animals.
With that, let's flip the page and turn to some more pleasant organisms.