Meeting Abstract

36.1  Wednesday, Jan. 5  Evolution of the annelid body plan: developmental insights from the unsegmented sipunculan worm Themiste lageniformis SEAVER, Elaine C.*; BOYLE, Michael J.; MEYER, Neva P.; University of Hawaii; Smithsonian Marine Station at Fort Pierce; University of Hawaii seaver@hawaii.edu

Sipuncula are a monophyletic group of coelomate marine worms. A growing number of molecular phylogenetic studies suggest that sipunculans belong within Annelida. The typical annelid body plan is overtly segmented, whereas sipunculans are non-segmented. Therefore, although these two lophotrochozoan groups may be closely related at the molecular scale, they are morphologically distinct from each other in many ways. To begin to understand the phenotypic transitions that have occurred over time between annelids and sipunculans, we investigated cellular and molecular differences in their developmental programs. In the sipunculan Themiste lageniformis, we examined the expression of ‘segmentation’ genes along with markers that characterize formation of the gut, mesoderm, nervous system and terminal growth. We then compared these data with similar studies in the polychaete annelid, Capitella teleta. Our results reveal that in some cases molecular coordinates are conserved between the two species. For example, in both species wnt1 is expressed in a small domain in the posterior of the body. In other cases, species-specific differences in the expression patterns of developmental regulatory genes can be explained by their association with particular anatomical features such as the gut, which is positioned in disparate parts of the body in Themiste lageniformis and C. teleta. By examining multiple developmental characters and making direct comparisons between a polychaete and a sipunculan, we aim to uncover molecular mechanisms underlying the diversity of body plans found within Annelida.