Linked from
The 10 pages that link to Mycoplasma, each with the reason it gives.
BacteriaBroader topic: They are bacteria that break the common pattern of a peptidoglycan wall.
Cell wallCompared with: Mycoplasmas show that bacteria can live without the usual rigid wall.
BacteriumBroader topic: They show that a bacterial cell wall is not universal.
Mycoplasma pneumoniaeNarrower topic: M. pneumoniae is one member of this broader genus.