Additional Author(s): Aoba Hosono
Published on SDB CoRe: Jun 29 2012
Tools & Techniques: Microscopy
Early Embryogenesis: Cleavage
Morphogenic Movements: Gastrulation; Neurulation
Morphogenesis: Cell Movements
Ectoderm-derived: Nervous System
Stage of Development: Embryo
Ascidians (sea squirts) are invertebrate chordates (subphylum Urochordata or Tunicata, class Ascidiacea). Ascidian eggs develop into tadpole larvae through a relatively simple manner of development with a small number of constituent cells. The larvae represent the basic body plan of chordates, having a dorsal neural tube and notochord flanked by bilateral muscle. The time lapse movie shows embryogenesis of Halocynthia roretzi from a fertilized egg to a hatched larva (35 hours of development). The movie highlights invariant cleavage patterns, gastrulation movements, closure of the dorsal neural tube at neurula stage, tail elongation, and sensory pigment cell formation in the brain. The notochord, a characteristic feature of chordata, is visible in the tail of the larva, consisting of exactly 40 cells in a single line. The total number of cells of the hatched larva is approximately 3000. The embryogenesis is invariant and cell lineages are well described. Embryos develop within the vitelline membrane. The diameter of the egg is 280 µm and the larva is 1.5 mm long.
Nishida, H. Specification of embryonic axis and mosaic development in ascidians. Dev. Dyn., 2005, 233:1177-1193.
Lemaire, P., Smith, W.C., and Nishida, H. Ascidians and the plasticity of the chordate developmental program. Curr. Biol., 2008, 18:R620–R631.