(amphioxus or lancelets): a model for understanding the evolution of chordate characters.
Cephalochordate (amphioxus) embryos: procurement, culture, and basic methods.
The present study is concerned with two cephalochordates representing different genera: namely, the Florida amphioxus, Branchiostoma floridae Hubbs, 1922, and the Bahamas lancelet, Asymmetron lucayanum Andrews, 1893.
For the cephalochordates considered here, the exceptionally long separation of the parent taxa--since the latter part of the Mesozoic Era--raises interesting questions about how the divergent gene regulatory networks from the two parents function together and how the hybrid genotype directs the development of the hybrid phenotype.
One of these speculations might have a chance of being correct if the basal cephalochordate was Branchiostoma-like in having Hatschek's left diverticulum; in that case the absence of the structure in Asymmetron would represent a loss in that evolutionary line.
The later embryos and larvae of cephalochordates have some unusual anatomical characters with names unfamiliar to most biologists.
The present discussion calls attention to the importance of settling the current disagreement about the course of evolution within the cephalochordates. The controversy could probably be resolved by adding nuclear genes to the phylogenetic analysis of the group and by sequencing the genome of a species of Asymmetron for comparison with that of Branchiostoma floridae (Putnam et al., 2008).
These data clearly demonstrate that Hb capable of reversible oxygen binding is expressed in two species of cephalochordates, thus expanding the known range of expression among chordates to include nonvertebrate chordates.
The existence of intracellular Hb dimers in cephalochordates is not unexpected because their nearest vertebrate relatives (the lamprey) also produce Hb dimers (12,13,14).
The endostyle is a specialized organ in the pharynx of tunicates, cephalochordates, cyclostomates, and certain prosobranchiates (Orton, 1912).
In future studies, we should use these probes to isolate endostyle-specific genes from cephalochordates, cyclostomes, and hemichordates.