Fig. 8.

Summary of mucin and FCGBP protein evolution. The VWD domain seems to occur in a restricted number of protists, but not in combination with the C8 or TIL domains. The combination of VWD/C8 appears in choanoflagellates and the structure characteristic of gel-forming mucins as well as the FCGBP_N-containing proteins appear in Ctenophora. The F5_F8 and CysD domains occur in Bilateria. A protein with FCGBP_N and multiple VWD–C8–TIL domains appears later in evolution as it is observed only in cephalochordates and vertebrates.