title: Xenoturbella bocki exhibits direct development with similarities to Acoelomorpha.
abstract: Xenoturbella bocki, a marine animal with a simple body plan, has recently been suggested to be sister group to the Acoelomorpha, together forming the new phylum Xenacoelomorpha. The phylogenetic position of the phylum is still under debate, either as an early branching bilaterian or as a sister group to the Ambulacraria (hemichordates and echinoderms) within the deuterostomes. Although development has been described for several species of Acoelomorpha, little is known about the life cycle of Xenoturbella. Here we report the embryonic stages of Xenoturbella, and show that it is a direct developer without a feeding larval stage. This mode of development is similar to that of the acoelomorphs, supporting the newly proposed phylum Xenacoelomorpha and suggesting that the last common ancestor of the phylum might have been a direct developer.
authors: Department of Biological and Environmental Sciences, University of Gothenburg, Kristineberg 566, SE-451 78 Fiskebäckskil, Sweden. h.nakano@kurofune.shimoda.tsukuba.ac.jp
authors: Hiroaki
authors: H
authors: Nakano
authors: Kennet
authors: K
authors: Lundin
authors: Sarah J
authors: SJ
authors: Bourlat
authors: Maximilian J
authors: MJ
authors: Telford
authors: Peter
authors: P
authors: Funch
authors: Jens R
authors: JR
authors: Nyengaard
authors: Matthias
authors: M
authors: Obst
authors: Michael C
authors: MC
authors: Thorndyke
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000648:ultrastructure; D005247:Feeding Behavior; D005306:Fertilization; D007814:Larva / Q000166:cytology / Q000254:growth & development; D018613:Microscopy, Confocal; D008954:Models, Biological; D008969:Molecular Sequence Data; D010063:Ovum / Q000166:cytology / Q000648:ultrastructure; D013550:Swimming; D014419:Turbellaria / Q000166:cytology / Q000196:embryology* / Q000502:physiology / Q000648:ultrastructure