Chordates and Hemichordates Evolution Quiz

The origin of chordates and hemichordates is a topic of great evolutionary and taxonomic in-ter-es-te. Chordates are a phylum of animals characterized by the possession of a notochord, a dorsal, hollow neural tube (nerve cord), branchial slits, an endostyle, myotomes, and a postanal tail. Hemichordates, on the hem-i-chord-ates, are a phylum of bilateral animals most closely related to chordates. Although hemichordates are not classified as true chordates, they share some similar traits and are closely related to chordates.

Chordates are classified into three subphyla: Urochordata (Tunicata), Cephalochordata, and Vertebrata. Urochordates, or "Tunicates," are characterized by a notochord, a dorsal neural tube, branchial slits, an endostyle, myotomes, and a postanal tail. Cephalochordates, or "acorn worms," are characterized by a notochord, a dorsal neural tube, branchial slits, an endostyle, myotomes, and a postanal tail. Vertebrates, or "chordates with a dorsal nerve cord," are characterized by a notochord, a dorsal neural tube, branchial slits, an endostyle, myotomes, and a postanal tail.

Hemichordates, on the hem-i-chord-ates, are classified into three classes: Enteropneusta (acorn worms), the most familiar living ones, and the pterobranchs. Hemichordates are distinguished by a tripartite (threefold) division of the body: a preoral lobe, a collar, and a trunk. Some DNA-based studies of evolution suggest that hemichordates are actually closer to echinoderms, which are also closely related to chordates.

Chordates and hemichordates share some similar traits, such as the possession of a notochord, a dorsal neural tube, and branchial slits. However, the development of chordates has been largely unstudied for 50 years, with a few exceptions. Modern phylogenies have established that the Hemichordata is a sister group to Echinodermata. The anteroposterior maps of gene expression domains for 38 genes of chordate neural patterning are highly similar for hemichordates and chordates, even though hemichordates have a diffuse nerve-net.

Chordates are thought to have originated from a common ancestor (or ancestors) of the deuterostomes. The prevailing view holds that the phylum Chordata consists of three subphyla: Urochordata (Tunicata), Cephalochordata, and Vertebrata. However, the taxonomic ranking of the three chordate groups themselves has not been intimately discussed.

Chordates and hemichordates have been studied for more than a century, but the origin and evolution of chordates have not been extensively discussed. The phylogeny of chordates has been a topic of great evolutionary and taxonomic in-ter-es-te, with four major scenarios proposed to explain chordate origin and evolution: the paedomorphosis hypothesis, the auricularia hypothesis, the inversion hypothesis, and the aboral-dorsalization hypothesis. Further studies of hemichordates and chordates are still in-ter-es-te to reveal the evolutionary origins of chordate traits such as the nerve cord, notochord, gill slits, and tail.

Hemichordates, with their tripartite body plan and similar larvae, could reveal the evolutionary origins of chordate traits. The anteroposterior maps of gene expression domains for 38 genes of chordate neural patterning are highly similar for hemichordates and chordates, even though hemichordates have a diffuse nerve-net. The change from the ancestor has occurred in the chordate line in the dorsoventral dimension, particularly in the centralization of the nervous system and the origination of the notochord; an inversion of the Bmp–Chordin axis might also have occurred.

Chordates and hemichordates are closely related, and their evolutionary origins are still a topic of great in-ter-es-te. Further studies of their gene sequences and expression domains, as hemichordates and chordates share some similar traits, could reveal more about the common ancestor and the origin of chordates. The phylogeny of chordates is still a topic of great evolutionary and taxonomic in-ter-es-te, with more studies and evidence still in-ter-es-te to support the prevailing view of the phylum Chordata and its subphyla.

Hemichordates, with their tripartite body plan and similar larvae, could reveal the evolutionary origins of chordate traits such as the nerve cord, notochord, gill slits, and tail. The anteroposterior maps of gene expression domains for 38 genes of chordate neural patterning are highly similar for hemichordates and chordates, even though hemichordates have a diffuse nerve-net. The change from the ancestor has occurred in the chordate line in the dorsoventral dimension, particularly in the centralization of the nervous system and the origination of the notochord; an inversion of the Bmp–Chordin axis might also have occurred.