not a fish, one is a fish, and the other is not a fish. Amphioxus is a chordate. It looks like a small fish, and its side is flat, about 5 cm long, translucent, with a pointed head and tail. There is a notochord in its body, including dorsal fin, gluteal fin and caudal fin. Living in coastal sediment, eating plankton. Amphioxus said it was a "fish", but it was not a fish. It is an animal between invertebrates and vertebrates, and tends to vertebrates. Amphioxus is a rare specialty in Xiamen, Fujian Province, commonly known as Crocodile Insect. It was once said that it was a myth that amphioxus was produced in Liuwudian. In history, amphioxus was the most popular after the shore. Amphioxus is a rare and precious marine wild cephalochordate, which is listed as the second-class key protected object in China.

Branchiostoma belongs to Chordata phylum Cephalopoda. 5 million years ago, the earliest transition from invertebrate to spine on earth-chordates appeared in the ocean. This is amphioxus, whose fins are scales and have no real fins. After a long time, amphioxus evolved into various vertebrates, including apes. Therefore, amphioxus is of world significance in species classification and fauna.