Jaw Morphology and Ontogeny in Five Species of Ophryotrocha Martin Oliver Macnaughton, 1 * Katrine Worsaae, 1 and Danny Eibye-Jacobsen 2 1 Marine Biological Laboratory, University of Copenhagen, Helsingør, Denmark 2 Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark ABSTRACT Detailed scanning electron microscopy of jaws within the genus Ophryotrocha (Dorvilleidae, Anne- lida) was performed on 871 jaw parts. The investigations resulted in new understandings of the ontogeny and jaw morphology and have systematic implications for the family. Five species in the genus (Ophryotrocha albor- ana, O. diadema, O. gracilis, O. hartmanni, and O. lab- ronica pacifica) were kept in culture, and the develop- ment of the jaws was studied by sampling throughout their life history. Ophryotrocha species have mandibular plates that remain the same throughout ontogeny, whereas the posterior shafts elongate. Both mandibular plate morphology and shaft ontogeny have species-spe- cific distinctions. In Ophryotrocha, the maxillae can be assigned to three to four distinct types, which are replaced by moulting. The maxillary morphology and de- velopmental stages at which moults occur are species specific, although with broad intervals. A redefinition is given for some of the basic jaw elements, and new homologies are proposed for structures that are also present across other dorvilleid taxa. J. Morphol. 271: 324–339, 2010. Ó 2009 Wiley-Liss, Inc. KEY WORDS: Dorvilleidae; ctenognath; mandibles; maxillae; moulting INTRODUCTION The complex pharyngeal jaw apparatus is an important diagnostic feature in Dorvilleidae (Purschke, 1987), a member of the order Eunicida, which is morphologically well characterized by the presence of ventral mandibles and dorsal maxillae (Orensanz, 1990; Rouse and Pleijel, 2001; Struck et al., 2006). Scolecodonts (fossilized polychaete jaw parts) assigned to the Dorvilleidae occur from the early Jurassic (around 200 million years ago; Szaniaw- ski and Gaz ´dzicki, 1978; Szaniawski, 1996), possi- bly making them the most ancient living represen- tatives of Eunicida (Orensanz, 1990; Paxton, 2000). During the Jurassic, a subgroup of several genera, including Ophryotrocha, gave rise to a divergence in the fossilized jaw record that has remained in the family to the present. Although most extant dorvilleids retain ctenognath P-type (from German: primitiv) maxillae, the divergent genera may, in the later stages of jaw ontogeny, form K-type (kompliziert) maxillae, where the ba- sal parts are greatly enlarged and resemble ice tongs. Between the ventral mouth opening and the dor- sal esophagus, lies the pharyngeal lumen with three sets of folds projecting rostrally into it (Purschke, 1987). The anteroventral- and postero- dorsal-most folds (pharyngeal and esophageal) sep- arate the pharynx proper from the mouth opening and esophagus, respectively. The middle folds carry the maxillary apparatus and are set apart from the other folds by a dorsal invagination. The two lateral sides of the fold are set off at the site of the maxillary plates and fuse sagittally at the beginning of the carriers. In the context of this ar- ticle, the term ‘‘carrier’’ is functional and used with the conditional that it is carrier-like, but homology to carriers in other families in Eunicida is neither implied nor denied. Ventral to the maxil- lae, the mandibles are anchored by the epithelium of a muscular pharyngeal bulb, and the anterior bulbous muscles attach to the posterior mandibu- lar shafts. A well-developed and complex system of musculature lies posterior to the mandibles, con- necting maxillary elements to the carriers, the mandibular muscles to the maxillary ones, and interconnecting to the musculature of the folds and bulbus, respectively. The hard jaw elements are complex structures, which are formed as sclerotized projections of the pharyngeal cuticle (see Fig. 1). The ventral mandi- bles are anchored by their shafts in deep epider- mal follicles in the bulbous muscular tissue (Tzetlin and Purschke, 2005) but have additional muscle attachments at the apophyses. The ante- Contract grant sponsor: Danish Natural Science Research Coun- cil; Grant number: FNU 272-06-0260. *Correspondence to: M.O. Macnaughton, Marine Biological Labo- ratory, University of Copenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark. E-mail: momacnaughton@snm.ku.dk Received 11 June 2009; Revised 12 August 2009; Accepted 16 August 2009 Published online 13 October 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jmor.10800 JOURNAL OF MORPHOLOGY 271:324–339 (2010) Ó 2009 WILEY-LISS, INC.