Lancelet Branchiostoma (formerly Amphioxus). This filter-feeding
cephalochordate superficially resembles a fish and clearly foreshadows
the evolution of vertebrates. Notice that the anterior end terminates
in a rounded projection called a rostrum. Behind this are the
oral cirri that direct food into the vestibule which leads to
the mouth. The mouth is located in a thin membrane called the
velum. Projecting forward from the base of the velum are several
finger-like, ciliated patches that comprise the wheel organ.
Behind the mouth is the large pharynx, which is perforated by
many gill slits supported by gill bars. Also note the dorsal
fin (supported by fin rays), the supporting notochord.les.