The "pneumoniae" group contains the clusters of "M. muris", "M. fastidiosum", "U. urealyticum", the currently unculturable haemotrophic mollicutes, informally referred to as haemoplasmas (recently transferred from the genera "Haemobartonella" and "Eperythrozoon"), and the "M. pneumoniae" cluster. This cluster contains the species (and the usual or likely host) "M. alvi" (bovine), "M. amphoriforme" (human), "M. gallisepticum" (avian), "M. genitalium" (human), "M. imitans" (avian), "M. pirum" (uncertain/human), "M. testudinis" (tortoises), and "M. pneumoniae" (human). Most, if not all, of these species share some otherwise unique characteristics including an attachment organelle, homologs of the "M. pneumoniae" cytadherence-accessory proteins, and specialized modifications of the cell division apparatus.