Branchiostoma lanceolatum, the European or Mediterranean amphioxus (also known as lancelet), is a marine invertebrate filter feeder belonging to the subphylum Cephalochordata, which, along with tunicates and vertebrates, forms the phylum Chordata. Cephalochordata is divided into three genera (Asymmetron, Epigonichthys, and Branchiostoma) encompassing at least 35 species. Currently considered the most basal group within the chordate lineage, the amphioxus Branchiostoma lanceolatum shares several key characteristics with vertebrates. These include a dorsal nerve cord, notochord, segmental muscles, perforated pharynx with gill slit, a post anal tail, and homolog of the pronephric kidney, and vertebrate adenohypophysis and thyroid gland. Amphioxus is widely distributed in sandy habitats of tropical and temperate seas, where it spends most of its lives buried in the sea floor. The embryonic and larval stages of amphioxus are planktonic, while the adults are benthic. Amphioxus is gonochoristic with distinct male and female animals, and the spawning season varies between species. Adult amphioxus with mature gonads can be artificially induced to spawn in the laboratory to achieve in vitro fertilization. Morphological distinctions among adults from various amphioxus species can be made by evaluating general body symmetry. Additionally, comparisons of the total count of muscle segments, dorsal and anal fin chambers, and pharyngeal slits serve as distinguishing factors. Over the last decades, amphioxus has emerged as a valuable model organism for developmental and evolutionary studies, and comparative genomics. Molecular and genomic studies have highlighted that amphioxus genome closely mirrors that of vertebrates, exhibiting similarity in both gene family content and genomic linkage. However, a crucial distinction lies in the fact that the amphioxus genome has not undergone the two rounds of whole-genome duplication commonly observed in vertebrate genomes. Therefore, the morphological and genomic simplicity of cephalochordates, in comparison to vertebrates, makes amphioxus an attractive model for studying chordate biology and gaining insights into the origin and evolution of vertebrates.