Cefalocordados

Cefalocordados, commonly known as lancelets or amphioxus, are a small subphylum of marine invertebrates belonging to the phylum Chordata. They are considered to be one of the closest living relatives to vertebrates, possessing key chordate characteristics throughout their lives. These characteristics include a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Lancelets are distinguished from other chordates by retaining these features into adulthood, a state known as paedomorphosis or neoteny.

These segmented, bilaterally symmetrical animals typically inhabit shallow, sandy or muddy bottoms in temperate and tropical seas worldwide. They are filter feeders, using their oral hood and tentacles to strain plankton and other organic particles from the water. Their burrowing behavior helps them find shelter and access food. Lancelets are generally small, ranging from 3 to 7 centimeters in length, with a translucent, fish-like body shape.

Historically, cephalocordates were significant in understanding the evolutionary links between invertebrates and vertebrates. Their unique combination of chordate features and simpler body plan made them valuable models for early developmental and evolutionary biology studies. While not as widely recognized as fish or mammals, lancelets play a role in marine ecosystems as detritivores and a food source for other organisms. The subphylum contains a single class, Leptocardii, with only a few genera and around 30 described species.