title: Cambrian suspension-feeding tubicolous hemichordates.
abstract: The combination of a meager fossil record of vermiform enteropneusts and their disparity with the tubicolous pterobranchs renders early hemichordate evolution conjectural. The middle Cambrian Oesia disjuncta from the Burgess Shale has been compared to annelids, tunicates and chaetognaths, but on the basis of abundant new material is now identified as a primitive hemichordate.
  
  
  
  Notable features include a facultative tubicolous habit, a posterior grasping structure and an extensive pharynx. These characters, along with the spirally arranged openings in the associated organic tube (previously assigned to the green alga Margaretia), confirm Oesia as a tiered suspension feeder.
  
  
  
  Increasing predation pressure was probably one of the main causes of a transition to the infauna. In crown group enteropneusts this was accompanied by a loss of the tube and reduction in gill bars, with a corresponding shift to deposit feeding. The posterior grasping structure may represent an ancestral precursor to the pterobranch stolon, so facilitating their colonial lifestyle. The focus on suspension feeding as a primary mode of life amongst the basal hemichordates adds further evidence to the hypothesis that suspension feeding is the ancestral state for the major clade Deuterostomia.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 2J7, Canada. karma.nanglu@alum.utoronto.ca.
authors.forename: Karma
authors.identifier: 0000-0002-0595-2225
authors.initials: K
authors.lastname: Nanglu
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 2J7, Canada.|Department of Natural History Palaeobiology, Royal Ontario Museum, Toronto, Ontario, M5S 2C6, Canada.
authors.forename: Jean-Bernard
authors.initials: JB
authors.lastname: Caron
authors.affiliation: Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Conway Morris
authors.affiliation: Département de sciences biologiques, Université de Montréal, Montréal, PQ H2V 2S9, Québec, Canada.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Cameron
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002816:Chordata, Nonvertebrate / Q000033:anatomy & histology / Q000145:classification*; D005580:Fossils; D005880:Gills / Q000033:anatomy & histology; D010802:Phylogeny
keywords: Burgess Shale; Cambrian; Enteropneusta; Hemichordata