Practice question

Branchiostoma amphioxus, commonly called lancelet, lives half-buried in sandy shallow seas, filter feeding via pharyngeal basket. Body laterally compressed, translucent, pointed at both ends, lacking distinct head, paired fins, cranium or pigmented eyes, with segmented chevron-shaped myotomes visible and continuous dorsal, ventral and caudal fins. Herdmania is tunicate urochordate with tunic and siphons, Petromyzon is cyclostome lamprey with sucking disc, Myxine is hagfish lacking vertebrae. Anatomical simplicity, absence of cranium and lifelong notochord clearly distinguish amphioxus as cephalochordate textbook example of basal chordate organization.