Micromacro Natural History

NH3008:The 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.