Chordata is divided into three subphylums, namely
1. Subphyla of Chordata, such as sea otters and sea otters.
2. Cephalopoda, such as amphioxus.
3. Vertebrate subphylum, which is divided into Cirrhonchus, Chondrichthyes, teleost, Amphibia, Reptilia, Birds and Mammalia.
Circadian is the lowest vertebrate, such as blind eel and lamprey, but they are not fish.
Fish is divided into two outlines:
One is cartilaginous fishes, such as sharks, Chinese sturgeons, manta rays, silver sharks, rays and so on.
Second, bony fishes, such as crucian carp, carp, perch, sole, hairtail and so on.
Therefore, amphioxus is not a fish, but a fish-shaped cephalochordate.
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