Meeting Abstract
Sipuncula (peanut worms) is an ancient group of marine worms with a global distribution, divergent life histories and a unique larval form, the pelagosphera. Life history patterns range from direct development without a larval stage to a conspicuous diversity of pelagic larval forms. Adult characteristics include a retractable introvert with a crown of tentacles, and a U-shaped digestive architecture. Recently, the unsegmented Sipuncula were relocated to an early branch within the tree of predominantly segmented annelid worms, such as polychaetes and earthworms. If they are truly members of Annelida, sipunculans provide an appropriate contrast for investigating the evolution of segmented body plans, and yet another example of flexibility among a broader group of animals that share a similar and directly comparable program of early development known as spiral cleavage (e.g. mollusks, annelids, nemerteans, sipunculans). In this presentation, confocal and compound light micrographs will showcase developmental diversity of sipunculan life history characteristics, with an emphasis on comparing ciliary, muscular and digestive organ systems. Comparative development of representative characters such as ciliary bands, circular and retractor muscles, or a functional gut suggest there are life history-specific ‘developmental priorities’ in the timing of essential behaviors such as swimming, crawling or feeding, respectively. Thus far, developmental evidence of segmentation within these and other organ systems is questionable. Complementary molecular studies are also in progress, and those efforts will be introduced to show how gene expression patterns and recent next-generation sequencing projects on comparative developmental transcriptomes are moving sipunculan worms forward as valuable research models.
