Question

What are the differences between Cephalochordates and agnathas? Why aren't cephalochordates included in agnathas?

Answer 1

Answer:

The key difference between Agnathans and Cephalochordates is that Agnathans are organisms that do not possess a jaw while Cephalochordates are organisms with jaws. This key difference plays a major role in the form of feeding they undergo. Agnathans are jawless fish. Cephalochordates are fish that have jaws.

Explanation:

acrania, any of more than two dozen species belonging to the subphylum Cephalochordata of the phylum Chordata. Small, fishlike marine invertebrates, they probably are the closest living relatives of the vertebrates. Cephalochordates and vertebrates have a hollow, dorsal nerve cord, pharyngeal gill slits, and a notochord. In most vertebrates, the embryonic notochord is eventually replaced by bony vertebrae or cartilaginous tissue; among cephalochordates, the notochord is retained into adulthood and is never replaced by vertebrae. There are about 20 species in two families, each with a single genus. Branchiostoma was formerly called Amphioxus, a name that is retained as an informal term. The other genus is Epigonichthys, also called Asymmetron. The genus Asymmetron is sometimes retained for some species. The cephalochordate fossil record extends back to about 525 million years ago during the early part of the Cambrian Period.

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Answer 2

Answer:

1. The key difference between Agnathans and Cephalochordates is that Agnathans are organisms that do not possess a jaw while Cephalochordates are organisms with jaws. ... Agnathans are jawless fish. Cephalochordates are fish that have jaws.
2. Cephalochordates have notochord and nerve cord present throughout life along the entire length of the body.