Fungal cell walls . Thus, NAG is present in all 3 Domains of life. Moore-Landecker, E. 1996. Fundamentals of the Fungi. Layers external to the cell wall .
Many bacteria produce extracellular layers that serve different functions in different critters.
Capsules help bacteria attach to surfaces - e.g. Streptococcus mutans attaches to your teeth using a capsule. Capsules also function as a protective layer - as in S. pneumoniae which can avoid phagocytyosis in the blood only if it has a capsule. The main functions of fimbriae are attachment and transport. The site of attachment of the flagellum to the cell wall is more complex, however. This motor is under complex control in bacteria.