Meeting Abstract
Pilidiophoran ribbon worms (phylum Nemertea), characterized by the planktotrophic, iconic pilidium larva, figure prominently among the biota of the Southern Ocean. We report on pilidiophorans collected by the British Antarctic Survey in the Weddell, Amundsen, and Bellingshausen Seas, as well as the Antarctic Peninsula and Scotia Arc, and by the New Zealand National Institute of Water and Atmospheric Research in the Ross Sea and Chatham Rise. Samples were collected by epibenthic sled or Blake trawl between 100 to 2100 meters and preserved in 95% ethanol. Of the 354 nemerteans collected, we generated 163 16s ribosomal DNA and 75 cytochrome oxidase subunit 1 DNA sequences and continue our sequencing efforts. The order Pilidiophora is represented by 62% of the sequences. Phylogenetic analyses reveal 10 distinct pilidiophoran lineages, including Baseodiscus antarcticus and two probable new species of Baseodiscus. Haplotype network analysis reveals that four of these 10 lineages have circumpolar distributions, of which one can be identified by proboscis morphology as Oligodendrorhynchus hesperides, whereas the others require further study. These four species match pilidial larval sequences deposited in GenBank by previous NIWA research that barcoded zooplankton. Pilidia of the Southern Ocean differ from those of other oceans in attaining unusually large sizes (up to 2 mm), and one species, Parborlasia corrugatus, is known to have a long larval phase. The pilidia have unusual morphological adaptations of the episphere and lappets that may favor long distance dispersal. Taken together these data suggest planktotrophic pilidia larvae are able to drift with the currents of the Southern Ocean and maintain genetic connections between vastly separated populations.
