Author

Linda Holland

Additional Author(s): Takayuki Onai

Published on SDB CoRe: Nov 14 2012

Organisms: Invertebrates
Early Embryogenesis: Blastula
Morphogenic Movements: Gastrulation; Neurulation
Morphogenesis: Cell Movements; Cell Shape Changes
Mesoderm-derived: Notochord; Somites
Ectoderm-derived: Nervous System
Organism: Amphioxus
Stage of Development: Embryo

Object Description

Embryos of amphioxus (Branchiostoma floridae) from blastula to early neurula. Animal pole is at the left. Amphioxus are marine chordates. They are the earliest diverging subphyla in the Phylum Chordata and thus hold clues to the origins of vertebrates. Amphioxus embryos gastrulate by simple invagination. At the late blastula stage (2.5 hr at 30°C), the vegetal half is distinguished by slightly larger blastomeres. At the onset of gastrulation (3.5 hr), the vegetal half of the embryo flattens and begins to invaginate into the animal half. By 4.0 hr, the mesendoderm has almost completely invaginated. At 4.3 hrs, the blastopore is open wide, but begins to close by 4.5 hr. There is no involution of tissues over the blastopore lip. By 5 hrs, the blastopore is nearly closed and the neural plate (np) has begun to flatten. In the mesendoderm, a single medial groove (arrowhead) and two dorsolateral grooves (asterisks) have begun to form. The medial groove will form the notochord and the dorsolateral ones will be partitioned into the anterior somites. At the early neurula stage (6.0 hr), the ectoderm on either side of the neural plate detaches from the neural plate and "walks" over it by means of lamellipodia (arrows). These sheets of ectoderm will fuse in the dorsal midline and then the neural plate will round up into the neural tube. WIREs Dev Biol 2012. DOI: 10.1002/wdev.11

References

Holland, L.Z., Onai,T. Early development of cephalochordates (amphioxus). WIREs Dev Biol, 2012, 1:167-183.

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