21. It has also proved difficult to produce a detailed classification within the living chordates . 22. The mycobacterial arabinogalactan is recognized by a putative immune lectin intelectin present in chordates . 23. Is it known what the primitive state of this ability in early chordates was? 24. FAM76A is conserved in most chordates but is not found in other regulating transcription. 25. Previous generations of scientists had thought that chordates evolved in the later Ordovician geological period. 26. The identification of the new specimen as a chordate will be controversial, scientists said. 27. On the basis of these findings, they constructed a new scenario for chordate evolution. 28. In the early embryonic stage, it looks like the hollow nerve cord of chordates . 29. If the ancestral chordates had perished, creatures with central nervous systems might never have developed. 30. In some chordates , it persists throughout life as the main ventral to the neural tube. 