coxiellaceae coxiellaceae the coxiellaceae are a family in the order legionellales. coxiellaceae coxiella burnetii, the causative agent of q fever scientific classification domain: bacteria phylum: pseudomonadota class: gammaproteobacteria order: legionellales family: coxiellaceae genera aquicella coxiella diplorickettsia rickettsiella "ca. berkiella" coxiella burnetii is a species in this order. another is rickettsiella melolonthae.