The Thaliacea is a class of Tunicata comprising three groups of pelagic tunicates, the Pyrosomida, Doliolida and Salpida. All are free-swimming holoplanktonic organisms with complex life histories and prodigious capabilities as filter-feeding herbivores in the plankton. These three orders have worldwide distributions yet together number fewer than 100 described species. In some cases phenotypic variability has confused prior efforts at systematic classification and left open the possibility of cryptic species among many seemingly cosmopolitan forms. Existing classifications and phylogenies are all based on a limited number of morphological characters, which have been inadequate to resolve many questions about relationships at the genus and species level. Preliminary genetic evidence suggests that the Thaliacea are monophyletic within the Tunicata and that salps, doliolids and pyrosomes are well-constrained monophyletic orders. However relationships below the ordinal are unclear, with some conflicts already arising between classical and molecular trees. Despite their global distribution and apparent ecological significance there are few scientists today working on any aspect of Thaliacean biology. Partly this may be due to the difficulty for non-specialists in identifying species, particularly as specimens are often damaged in collection. This project brings together two molecular zoologists and one expert in Thaliacean ecology and life history. The research team will seek to reconcile morphological and genetic data to develop a phylogeny for the Thaliacea, based on data from as many of the described species as can be obtained, probably at least 70%. Because these groups are fairly small, this is a feasible goal, and will enable not only a well-supported consensus phylogeny and classification, but also a monographic treatment of the Class that will be useful for species identification by nonexperts. Broader impacts of the proposed research include the contribution of results to the global Census of Marine Zooplankton and the provision of a practical identification guide to Thaliacea for biological oceanographers. The project will support a postdoctoral investigator at WHOI and involve undergraduate students at the University of Connecticut. Project objectives and results will be made widely available via one or more websites hosted at WHOI or the University of Connecticut.
