The word Cephalochordata is formed from the Greek word Kephale meaning head and chorda meaning chord. They are commonly called lancelets. First they are described as Amphioxus (amphi = both means both ends, ends = oxys means sharp). Later, according to the law of precedence, they were named Branchiostomata (branchia = gill, stoma = mouth). Cephalochordates are called invertebrate chordates. In 1774 scientist Peter Simon Pallas (1774) described Branchiostoma lanceolatum. Their number of species is 33.