Branchiostoma

Branchiostoma is a genus of lancelets, small, laterally compressed marine animals that belong to the subphylum Cephalochordata. Commonly called amphioxus, they are filter feeders that inhabit shallow coastal sands and muds in temperate and tropical seas. Branchiostoma species are transparent to pale; individuals range from 2 to 5 centimeters long, with a pointed anterior oral hood and a series of gill slits along the pharynx.

Anatomy: Like other cephalochordates, Branchiostoma retain a notochord that extends along most of the body, a dorsal hollow nerve cord, segmented myomeres, and a pharynx with numerous gill slits. Water is drawn in through the mouth and pharyngeal slits, passes into a surrounding atrial cavity, and exits via the atriopore. They lack paired fins and jaws, but possess sensory tentacles and cirri around the mouth. The endostyle secretes mucus for filter feeding. Development includes a free-swimming, tadpole-like larva before metamorphosis to an elongate, eel-like adult.

Taxonomy and biology: Branchiostoma is one of the main cephalochordate genera, alongside Asymmetron. The genus includes several species, notably Branchiostoma lanceolatum (European amphioxus) and Branchiostoma floridae (the Florida amphioxus), with others in the Indo-Pacific. Branchiostoma species have long been used in studies of vertebrate origins and early chordate evolution; their genome and embryology provide insight into the evolution of the vertebrate nervous system, notochord, and sensory structures.

Habitat and distribution: Branchiostoma species occur in shallow seas, typically buried in sandy or muddy substrates, from temperate to tropical regions. They are sensitive to environmental conditions and are often used as indicators of coastal ecosystem health.