Chupacabra: Depending on the canid or the humanoid, it would probably be Canus vampyrus or Saurosapiens vampyrus
Mermaid: Homo piscis
Centaur: Homo equus
Selkie: Pinnipedia sapiens or Homo pinnipedia
Siren: Homopteryx musicis
Manticore: Leomorph scorpiones