 An example is chitin a very durable structural protein used in surgical sutures as well as durable varnishes but is common to many animals especially crustaceans and insects.But is also found in the African clawed frog ("Xenopus laevis").Wagner et al., suggest that chitin might have a microscopic function observed in cell to cell signaling and the manufacture of insect cuticle for example might represent a recurrent change in the location of expression chitin
Speculative, but however Chitin synthase is maintained in many lineages where it does not have an obvious macroscopic function.