This video says about itself:
Amphioxus embryonic development from fertilization to mid-neurula. The movie was done at the Laboratoire Arago, Banyuls sur Mer, France, by Alain Camasses and Hector Escriva.
From the University of California – San Diego, in the USA:
Fluorescent proteins found in nature have been employed in a variety of scientific research purposes, from markers for tracing molecules in biomedicine to probes for testing environmental quality. Until now, such proteins have been identified mostly in jellyfish and corals, leading to the belief that the capacity for fluorescence in animals is exclusive to such primitive creatures.
Scientists at Scripps Institution of Oceanography at UC San Diego have discovered fluorescent-light emitting features in an evolutionarily important marine organism and say such a capacity may be much more prevalent across the animal kingdom than previously believed.
In the cover story of the October issue of Biological Bulletin, Dimitri Deheyn and his colleagues in La Jolla, Calif. and Japan describe finding green fluorescent proteins (GFPs) in amphioxus, a fish-like animal closely studied by scientists due to its evolutionarily important position at the base of a large phylum of animals called chordates. The researchers say amphioxus’ GFPs are very similar to those of corals, an interesting fact since the two animal groups are separated by hundreds of millions of years of evolution.
The finding emphasizes the idea that evolutionary preservation of fluorescence must play an important ecological function, Deheyn said. Many animals haven’t been tested for fluorescence and its prevalence in the animal kingdom remains unknown.