text: [MARINE_BIOLOGY_INTERNATIONAL] Study Sheds Light On Tunicate Evolution | Science News
  [MARINE_BIOLOGY_INTERNATIONAL] Study Sheds Light On Tunicate Evolution
  Woods Hole, MA  Woods Hole Oceanographic Institution (WHOI) researchers have filled an important gap in the study of tunicate evolution by genetically sequencing 40 new specimens of thaliaceans, gelatinous, free-swimming types of tunicates. Tunicates are a phylum of animals closely related to vertebrates, with a firm, rubbery outer covering called a tunic, from which the name derives.
  There are approximately 72 described species of thaliaceans classified in three subgroups--the pyrosomes, salps, and doliolids, all of which are planktonic open-ocean animals that people seldom see. Govindarajan and her colleagues found a close relationship between thaliaceans and other types of tunicates, including sea squirts--bottom-dwelling tunicates that commonly overgrow docks and pilings.
  "The Thaliacea was monophyletic, indicating that the pyrosomes, salps, and doliolids arose from a common ancestor," she said. "Within the salp lineage, we unexpectedly found the cyclosalp group to be closely related to another salp lineage, despite many morphological and behavioral differences. We also were able to clarify the uncertainty around the salp Weelia (Salpa) cylindrica. Previous work suggested that this species was closely related to species in the genus Salpa, but our results strongly indicated that it is distinct and warrants placement in a separate genus."
  Previous tunicate studies have been based on18S rDNA sequences, but thaliaceans were very poorly represented, Govindarajan said. "There are relatively few thaliacean specialists, and specimens are difficult to obtain and identify. Better thaliacean representation allowed us to make new insights on evolutionary relationships both within the Thaliacea and between thaliaceans and other tunicates."