Jaw Mineralogy in Eunicean Polychaetes (Annelida)

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Abstract
X-ray diffraction analysis of jaws from representatives of five fmilies of eunicean polychaetes indicates that three different types of mineralization are represented. Aragonite is reported for the first time from species within the families Onuphidae and Eunicidae. Jaws of species in the Lumbrineridae are mineralized with calcite, as are those of Lysarete. Other lysaretids and members of the Arabellidae have jaws which are amorphous to X-rays, as are those of the unrelated glycerids and nereidids. In combination with other morphological characters, the mineralogy of the jaws is a useful taxonomic character within the superfamily Eunicea at the family level. The calcified jaws and those of the nereidids are weakly sclerotized, and may have relatively low fossilization potential. This may explain the relative rarity of polychaete jaws in post-Devonian rocks in contrast to the abundance of jawed polychaetes in the modern oceans.