Cambrian suspension-feeding tubicolous hemichordates
Karma Nanglu Email author View ORCID ID profile, Jean-Bernard Caron, Simon Conway Morris and Christopher B. Cameron
BMC Biology201614:56
DOI: 10.1186/s12915-016-0271-4 © Nanglu et al. 2016
Received: 4 April 2016Accepted: 8 June 2016Published: 7 July 2016
Abstract
Background
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.
Results
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.
Conclusions
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.
Keywords Enteropneusta Hemichordata Cambrian Burgess Shale
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