Jaw growth and replacement in 'Diopatra aciculata' (Annelida:Onuphidae)

Abstract

Jaw development was studied in 1- to 45-day old 'Diopatra aciculata' (fertilisation to 44-chaetigers). Both mandibles and maxillae became visible in 4- to 6-chaetiger worms. The initial protomandibles become embedded in the adult mandibles. The larval maxillae consist of a left fang-like and right small serrated element, a pair of serrated plates, distal ridges, and a single carrier. Larval maxillae were replaced by juvenile maxillae in 14- to 15-chaetiger worms. Juvenile maxillae have adult-like carriers, MII and MIV, but MI are proximally dentate with a distal hook; MIII and MV are absent. First adult maxillae were seen in 21-chaetiger worms. Each subsequent moult results in larger but otherwise identical apparatuses. The moult increment (difference in size between successive moults) was established as 1.34 and used to extrapolate estimates of size classes. Based on these calculations our largest worms had their fourth set of adult maxillae, having moulted the adult maxillae every three to four days.