Meeting Abstract

S3-1.6  Jan. 4  New light on an old problem: Insights into the development and evolution of the chaetognaths MATUS, D.Q.*; HEJNOL, A.; DUNN, C.W.; HALANYCH, K.M.; MARTINDALE, M.Q.; Kewalo Marine Laboratory, Univ. of Hawaii; Kewalo Marine Laboratory, Univ. of Hawaii; Kewalo Marine Laboratory, Univ. of Hawaii; Auburn Univ., Auburn; Kewalo Marine Laboratory, Univ. of Hawaii matus@hawaii.edu

Chaetognaths, or arrow worms, are one of the most ubiquitous and abundant members of pelagic zooplankton communities. In spite of this, they have remained one of the most recalcitrant groups of organisms to place within the metaozoan tree. They possess a suite of morphological and developmental characters that ally themselves with the deuterostomes, including a posterior blastoporal fate, a holoblastic radial cleavage program, a tri-partite coelomic arrangement, enterocoely, and a post-anal tail. However, molecular phylogenetics fail to find any affinity between the chaetognaths and the deuterostomes, despite being ambivalent about their placement within the protostomes. We have attempted to resolve the group�s phylogenetic position through a large-scale analysis of a conserved set of nuclear genes isolated from the pelagic chaetognath, Flaccisagitta enflata, via Expressed Sequence Tags (ESTs), since more traditional molecular phylogenetic approaches (e.g., 18S/28S ribosomal DNA) have failed to resolve their position within the protostomes. Additionally, we have isolated key developmental regulatory genes involved in axial patterning and mesoderm formation and are examining their expression via in situ hybridization to investigate both conserved and novel patterns of expression throughout development.