A small (6-7 cm.) fish-like animal that some consider to be the precursor of the vertebrates. Also known as amphioxus (from the Greek for "both (ends) pointed" or lancet worm. There are 22 known species of lancets belonging to two families:
Phylum: Chordata
Class: Cephalochordata (sometimes considered a subphylum)
Family: Branchiostomidae (formerly Amphioxus) and Epigonichthyidae (formerly Asymmetronidae)
Lancets spend most of their time buried in sand where they feed on detritus. They resemble fish in many ways: a streamlined body, a notochord, separate sexes, and a dorsal fin that extends around the tail as a caudal fin and continues underneath the body as a ventral fin. However, they have neither bones nor cartilage and only the tiniest vestige of a brain. They are filter feeders, using cilia to drive water through the mouth and out the gill slits where food particles are trapped.