SYSTEMATIC BIOLOGY
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RELATIVE NUMBERS OF LIVING CRANIATE SPECIES BY CLASS

The nine craniate classes with extant taxa together have more than 54,703 living species.  Clearly, the Osteichthyes is, by far, the most speciose class with almost half of the known species.  The Myxini and Petromyzontida each has less than 0.5% of the living Craniates.