Additional Author(s): Nick Putnam
Evolutionary Developmental Biology: Origins of Complexity; Genomic Evolution
Stage of Development: Adult
Four adult amphioxus (Branchiostoma floridae). Shown are three females (top) and one male (bottom). Anterior is to the left, dorsal up. Amphioxus, also known as lancelets, are marine animals that grow to a maximum size of ~5 cm. Their development is particularly rapid—under three months from fertilized egg to sexually mature adult. They have 26-28 gonads on each side of their body which are visible through the body wall ventrally.
Amphioxus are the earliest diverging chordate subphylum, and thus are the sister group to the urochordates (tunicates) plus vertebrates. This phylogenetic position, plus the finding that its divergence predates the two rounds of whole genome duplication in the chordate lineage, allows amphioxus to serve as a genomic surrogate for the proto-vertebrate ancestor (Putnam et al., 2008).
Putnam, N.H., et al. The amphioxus genome and the evolution of the chordate karyotype. Nature, 2008, 453: 1064-1071.