Jaw growth and replacement in Polychaeta

Mandibles and maxillae of Australonuphis teres (family Onuphidae) continue to grow throughout life without replacement. Mandibles are solid structures that grow by external depositions, leaving a series of growth rings. Maxillae are hollow without any growth rings. New teeth are added to a maxilla by the division of its most distal tooth. Overall growth of the maxillae is thought to occur from the inner epidermal layer of the cavity. The same mode of growth is expected in all extant Eunicoidea with exception of Dorvilleidae, where maxillae are periodically replaced.