The name "Haikouichthys" comes from the Greek: "Ichthys" which means fish "Fish of the Chinese city of Haikou". And you put that name is very characteristic. I mean, a fish is a fish, and you do not name it except that fish being fish special. And here it is ... because the Haikouichthys is the first fish of evolution. Not only that, it is also one of the first vertebrates that existed, and which all others come from trout, shark, elephant, hen, you and me.
Anyway, this post, the first vertebrate, the first fish of prehistory, he shares with his contemporary, the Pikaia. Both of others lived in the Cambrian, appeared at the beginning of the famous Cambrian explosion of life. 530 million years ago.
The Haikouichthys, was not a giant of the oceans, in fact, was about 2.5 cm (3 in). With your thumb we could have ended the life of one of the most important animal in the history of evolution.
(It occurs to me cuanticocosmictemporal dysfunction, if we traveled back in time to 530 million years ago and we killed the fish in Haikou that evolved in all vertebrates, we would not exist, and therefore we could not kill the Haikouichthys, so he would survive and we too .... anyway ... I do not follow me head implodes and the blog is not about that).
A further feature is that Haikouichthys had a distinct head of the body. Until then, prehistoric animals seemed tubes, it was not known or where to eat or where defecated ... at first glance. And far fewer had a clear center differential that controlled the other body part. But with the Haikouichthys this was more evident. Had a head, eyes and mouth of millimeters. And then a "long" body with dorsal and pectoral fin that served to move like fish in water.
The movement is really important. We must bear in mind that at the beginning of the Cambrian, most of the oceans was occupied by large arthropods, sponges or slow and slimy worms. And suddenly, a small chordate appears, a young vertebrate with a capacity that others had: was agile and quick. And though not great, thanks to its speed and agility, he could escape their large predators and become the main protagonist in the formation of large animal phyla: vertebrates.