the root (no rank)
Viruses (domain)
retroid viruses (subkingdom)
Retroviridae (family)
Orthoretrovirinae (subfamily)
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Alpharetrovirus (genus)
Betaretrovirus (genus)
Deltaretrovirus (genus)
Epsilonretrovirus (genus)
Gammaretrovirus (genus)
Lentivirus (genus)