Nitrosopumilus piranensis is a marine ammonia-oxidizing archaeon in the phylum Thaumarchaeota, isolated from sediments in the Adriatic Sea near Piran, Slovenia. Like other Nitrosopumilus species, it performs chemolithoautotrophic nitrification by oxidizing ammonia to nitrite and is highly abundant in marine environments. Its discovery contributed to our understanding of archaeal diversity in coastal sediment ecosystems.