title: The development of the enteropneust hemichordate Balanoglossus misakiensis KUWANO.
abstract: We describe development from fertilization to metamorphosis of the enteropneust hemichordate Balanoglossus misakiensis. This is the first report to describe the complete development of an indirect-developing hemichordate under laboratory conditions. Mature adults were induced to spawn by shifting the temperature of seawater from 23 to 28 degrees C. Eggs (200 microm diameter) were enclosed within a non-mucilaginous membrane, and dispersed readily in seawater. After artificial insemination, a fertilization envelope was elevated from the egg surface beneath the egg membrane; this was followed by the formation of the first and second polar bodies within the envelope. Zygotes cleaved at 20-min intervals to form blastulae, and gastrulation started 9 h after fertilization. Embryos hatched 1 day after fertilization to become typical feeding tornaria larvae. The larvae metamorphosed 7-10 days after fertilization without undergoing the first (Müller) or forth (Krohn) stage of indirect-developing hemichordate development. Larvae that were not fed failed to metamorphose. Juveniles completed adult body formation within a week of settling in sand at the bottom of the culture tube. We discuss heterochronical modifications of B. misakiensis development, and make the case for this species as a potential model organism for the investigation of indirect-developing hemichordates.
authors.affiliation: Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Japan. urata@bio.sci.osaka-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Urata
authors.forename: Masaaki
authors.initials: M
authors.lastname: Yamaguchi
mesh_terms: D000818:Animals; D002970:Cleavage Stage, Ovum / Q000502:physiology*; D007448:Invertebrates / Q000196:embryology* / Q000502:physiology; D007564:Japan; D007814:Larva / Q000254:growth & development; D008675:Metamorphosis, Biological / Q000502:physiology*; D010063:Ovum / Q000166:cytology*; D013997:Time Factors