The protochordates (amphioxus and tunicates) occupy a pivotal position in chordate phylogeny, being the closest living invertebrates to the vertebrates. In spite of their evolutionary significance, these animals do not feature commonly in modern developmental biology research. This has not always been the case; indeed, amphioxus ranked as one of the principal animals for embryological description in the early part of this century. The ascidia (one group of tunicates) have received intensive study as a model for determinative development, and considerable experimental and molecular data have been accumulated over the past few decades (1).
The realization that many genes playing key roles in early development have been widely conserved in animal evolution has helped bring protochordates back toward the mainstream of developmental biology research. The existence of homologous control genes in divergent species is a starting point for investigating evolutionary changes in developmental control; ascidia and amphioxus are a natural choice for inclusion in such studies, since they occupy such important phylogenetic positions.
Here we give protocols for obtaining embryos and larvae of one ascidian species, Ciona intestinalis, and one amphioxus species, Branchiostoma floridae.
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