Cephalochordates (amphioxus or lancelets): a model for understanding the evolution of chordate characters.
The amphioxus genome illuminates vertebrate origins and cephalochordate biology.
The intermediate degree of gill slit deflection in the hybrid cephalochordates
would be particularly interesting to study because of existing background information on pharyngeal patterning in Branchiostoma species (Holland and Holland, 1996; Escriva et al, 2002; Schubert et al.
The later embryos and larvae of cephalochordates
have some unusual anatomical characters with names unfamiliar to most biologists.
Recent genomic comparison has provided evidence that urochordates, not cephalochordates
, represent the closest living relatives of vertebrates (Delsuc et al, 2006), although this has been contended (Bourlat et al.
It is present in urochordates, cephalochordates
, and larval lampreys, and its function is secretion of a mucous net to retain particles during feeding (Olsson, 1965; Deibel and Powell, 1987; Hiruta et al.
, urochordates, hemichordates, and echinoderms); but complete genome sequences have not yet been obtained for species representative of these phyla.
The myotome tissue of cephalochordates
consists of chevron-shaped bundles of cells, and the notochord tissue consists of a lamellar structure of stacked cells surrounded by a fibrous sheath.
The transmission electron micrographs suggest that the contractile vessel-like structure in the ventral midline of larval cephalochordates
is not the sub-intestinal blood vessel, but rather the ventral coelom.
The endostyle is a specialized organ in the pharynx of tunicates, cephalochordates
, cyclostomates, and certain prosobranchiates (Orton, 1912).
A homologous structure may also occur in cephalochordates
(Lacalli, 1994; Lacalli et al.