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How are chordates related to echinoderms?
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Chordate
X-ray fish (Pristella maxillaris), is an example of a chordate with a visible backbone.
Chordates and echinoderms are related as members of the Deuterostomia, a major group of animals classified together based on shared embryological development and molecular criteria.1
The relationship is defined by several key developmental characteristics:
- Embryonic Development: In both groups, the mouth develops from an opening other than the blastopore, which instead becomes the anus.1
- Coelom Formation: Both phyla are coelomates, meaning they possess a fluid-filled body cavity lined with mesoderm. In both echinoderms and primitive chordates like amphioxus, the coelom forms through the development of outpocketings from the embryonic gut (archenteron).12
- Evolutionary Lineage: Some zoologists propose a "diphyletic" theory of evolution, which suggests that higher metazoans diverged into two main lines of descent: one leading to annelids, arthropods, and mollusks, and the other leading to echinoderms and chordates, both of which are thought to have emanated from an ancient flatworm ancestor.3
While they share these fundamental developmental patterns, they are distinct phyla with unique anatomical features, such as the chordate notochord and the echinoderm water-vascular system.43