Function of the pseudomaxillary fold in the mouth opening of the coelacanth, Latimeria chalumnae

The oral region of a coelacanth, Latimeria chalumnae, from the Comoro Islands, was examined in fresh condition, and the complex folding of the membrane between the lower jaw and the skull, and a strut-like structure in the membrane were found. When the mouth opened, the pseudomaxillary folds covered the lateral walls of the mouth. The movement of the membrane is inferred from the observation of the specimen. Coelacanths developed a way of covering the lateral sides of mouth that is different from that of other fishes; especially the pseudomaxillary fold above the strut is unique to coelacanths, but the pseudomaxillary fold below the strut is similar to the lower lip fold of the lepidosirenoid lungfish.