Amphioxous and Lancelets (Cephalochordata)

The Cephalochordata are most known for their relation to basal vertebrates.  The adult from provides insight in to intermediary structures between invertebrates as they are one step closer to the Vertebrata than the Tunicates.  This Chart shows stages through development (1 – 12) with tissue derived from the ectoderm coloured grey, from the endoderm coloured grey-green and the mesoderm coloured yellow.  Using the longitudinal section of the adult (14) note the four typical chordate features the pharyngeal gill slits (SF), dorsal, hollow nerve cord (starting at NP), notochord (Ch) and post-anal tail (posterior to A).