Amphibia/Seiren is the eighth Cardian whos name comes from the Italian word, "Sirena". Alan and Ann send to gather energy for the Doom Tree. She is a mermaid that has pink hair that can extend and constrict enemies and drain their energy She can also shoot blasts of water from her mouth and use a pollen powder that can put anyone who touches it to sleep. She appeared in Episode 8 of Sailor Moon R.
Alan and Ann summoned Amphibia at the Autumn Festival after raising the audience's energy level when Sarah Howe convinced them to dress up as aliens for the fashion show. Amphibia made everyone fall asleep with her powder but Serena, Amy, Raye, Lita, and Mina escaped the attack. Amphibia used her hair to drain Raye's energy but the others transformed and stopped her. Amphibia began draining their energy but Raye transformed into Sailor Mars and stopped her attack with Mars Fire Ignite however, this was not enough to destroy her. Just then, Moonlight Knight appeared and stopped Amphibia's attack. When she swung her tail and knocked over the music that Raye worked so hard on, Sailor Mars used a new technique, the Mars Firebird Strike, to damage Amphibia and restore the other Sailor Scouts' energy. Sailor Moon then destroyed Amphibia with her scepter.
- Amphibia could only repeat her name in the original version but int he English dub she is capable of speaking.