Deuterostome

Deuterostome

Phylogenetic tree showing the major deuterostome groups

A deuterostome is a member of a major evolutionary lineage of animals that includes vertebrates (such as fish, amphibians, reptiles, birds, and mammals) as well as some invertebrates. The name "deuterostome" comes from the fact that during embryonic development, the first opening that forms becomes the anus, while the second opening becomes the mouth. This is in contrast to protostomes, where the first opening becomes the mouth.

Evolutionary History

Deuterostomes first appeared in the fossil record during the early Cambrian period, approximately 540 million years ago. They are believed to have evolved from a common ancestor with protostomes, which are another major group of animals. The exact relationship between deuterostomes and protostomes is still a subject of scientific debate.

Classification

Deuterostomes are divided into several major groups, including:

Chordates

Phylogenetic tree showing the major chordate groups

Chordates are a subphylum of deuterostomes that includes all vertebrates. They are characterized by the presence of a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail at some point during their development. Chordates are further divided into several classes, including fish, amphibians, reptiles, birds, and mammals.

Echinoderms

Diversity of echinoderms

Echinoderms are a phylum of deuterostomes that includes starfish, sea urchins, sea cucumbers, and sea lilies. They are characterized by their radial symmetry, a water vascular system, and a unique endoskeleton made of calcified plates. Echinoderms play important roles in marine ecosystems and have a fossil record dating back to the early Cambrian period.

Hemichordates

Hemichordates are a phylum of deuterostomes that includes acorn worms and pterobranchs. They are marine animals that exhibit a combination of chordate and echinoderm-like characteristics. Hemichordates are considered to be the closest living relatives of chordates and provide valuable insights into the evolutionary transition between invertebrates and vertebrates.

Importance

Deuterostomes, particularly chordates, have had a significant impact on the evolution and diversity of life on Earth. Vertebrates, which are a subgroup of chordates, have colonized almost every habitat on the planet and have evolved a wide range of adaptations for survival. They play crucial roles in ecosystems as predators, prey, and ecosystem engineers.

See Also

• Protostome
• Evolution of vertebrates
• Phylum Chordata
• Phylum Echinodermata
• Phylum Hemichordata