Question

Are cephalochordates vertebrates?

Answer 1

Cephalochordates are chordate animals that belong to the Cephalochordata subphylum. They're also known as amphioxus or lancelets. They are chordates with all five synapomorphies, which are traits shared by all chordates in their larval or adult stages.

Complete answer:
Cephalochordate, also known as acrania, any of the more than two dozen species in the phylum Chordata's subphylum Cephalochordata. They are tiny, fish-like marine invertebrates that are possibly the vertebrates' closest living relatives. A hollow dorsal nerve cord, pharyngeal gill slits, and a notochord are found in cephalochordates and vertebrates.Lancelets (Cephalochordata) are aquatic species that share many of the characteristics of chordates, with the exception that the notochord extends into the brain.

The embryonic notochord is gradually replaced by bony vertebrae or cartilaginous tissue in most vertebrates; however, the notochord is preserved in cephalochordates until adulthood and is never replaced by vertebrae. There are approximately 20 species divided into two families, each with its own genus.

The vertebrates are the most well-known chordate group. In addition to the Vertebrata subphylum, the phylum Chordata comprises two invertebrate subphylum: Urochordata and Cephalochordata. At some point during their growth, members of these groups also have a notochord, a dorsal hollow nerve cord, pharyngeal slits, post-anal tail.Urochordates and cephalochordates, unlike vertebrates, never grow a bony backbone.

The lancelets, named for their blade-like appearance, are the only living members of Cephalochordata. Lancelets are small, buried in sand at the bottom of warm temperate and tropical seas, and are only a few centimetres long. They are suspension feeders, much like tunicates. The lancelet and Pikaia, which have notochords and paired muscle blocks, may belong to the chordate group of animals from which vertebrates descended.

No, they are not vertebrates. About 700 and 650 million years ago, they separated from the rest of the chordate subphylum.

Note: While they lack a true brain, the notochord extends into the head, giving the subphylum its name ("cephalo" is Greek for "head"). Pikaia, the oldest known cephalochordata, is an extinct member of this subphylum. Pikaia fossils were discovered in Canada's Burgess shales and dated to the middle of the Cambrian period, indicating that they are over 500 million years old.