STRUCK, T.S.*; Auburn University, Auburn: Annelid rDNA phylogeny and implications for progenetic origins

Annelids show a broad range of length from only a few hundred �m up to 6 m. Some small, meiofaunal polychaetes, such as Dinophilidae, some �Dorvilleidae� (e.g., Parapodrilus), Protodrilida, exhibit morphological simplicity in that they lack features typical of larger polychaetes, for example parapodia and/or head appendages. Due to the general resemblance of adult meiofaunal stages to juveniles of larger forms, paedomorphic processes, like progenesis, have been invoked to explain the evolutionary origins of such taxa with increasing frequency over the past four decades. The phylogenetic assessment of �simplistic� meiofaunal forms based on morphological data is often ambiguous. Autapomorphic characters uniting one or the other of these taxa with a specific annelid taxon are often missing. This is usually due to the reason that the larval and juvenile characters, which support the hypothesis of progenetic origin, can also be found in several other annelid taxa. In this presentation the phylogenetic position of hypothesized progenetic taxa will be examined using molecular data. Specifically rDNA data will be used to test the hypothesized progenetic origin of different meiofaunal taxa, like Protodrilida, Dinophilidae and the dorvilleids Parapodrilus and Microdorvillea. In some cases (e.g., Parapodrilus and Microdorvillea) the molecular phylogeny is consistent with the hypothesized progenetic origin and thus gives additional evidence for this evolutionary scenario. In Dinophilidae and Protodrilida the results seem to refute the supposed progenetic origin. However, I will also exemplify the limitations of the molecular approach. Although molecular data are usually more accurate in the phylogenetic assessement of these taxa than morphological data, morphology on the other hand is a necessity to substantiate the hypothesis of progenesis.