A bulla is an attachment organ that is usually formed after initial attachment of the parasite to the host. Host tissue is penetrated and part of the parasite is inserted. Transformation of the embedded part of the parasite occurs to complete the formation of the bulla. The result is effectively an anchor deep within the host and provides very secure attachment.
Salmincola forms its bulla from modified mouthparts, and uses it to attach to the external surface of fish.
