The notochord divides the animal kingdom

The idea

By absence or presence of a notochord, a flexible rod-shaped structure, animals are non-chordata (invertebrates) or chordata; chordata comprise protochordata and vertebrata, and in some chordates the notochord precedes the vertebral column.

A rod inside

Some animals have a flexible rod-shaped structure inside the body. Others do not.

What do you think scientists can do with this difference?

• Use it to divide animals into two big groups
• Use it to decide the animal's colour
• Use it to decide where it lives

Splitting Animalia

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Present or absent

The notochord splits the animal kingdom first into two. In some chordates the notochord comes before the vertebral column, the backbone, which forms later.

By the absence or presence of a notochord, a flexible rod-shaped structure, animals are non-chordata (invertebrates) or chordata; chordata comprise protochordata and vertebrata, and in some chordates the notochord precedes the vertebral column.

Notes

Animals are non-chordata (invertebrates) or chordata by absence or presence of the notochord; chordata are protochordata and vertebrata.

Check yourself

What is the notochord?

Animals without a notochord are called ...

Chordata are further divided into ...

In some chordates, the notochord ...

• A hard shell outside the body. The notochord is a flexible rod-shaped structure, not a shell.
• A tissue that carries water. Xylem is the tissue that carries water in plants.
• A flexible rod-shaped structure — correct. Yes!
• non-chordata (invertebrates) — correct. Yes!
• chordata. Chordata are animals that have a notochord.
• vertebrata. Vertebrata are chordates with a vertebral column.
• fish and amphibians. Fish and amphibians are two of the five groups of vertebrates.
• protochordata and vertebrata — correct. Yes!
• Porifera and Cnidaria. These are two groups of non-chordata.
• replaces the brain. The book says the notochord acts as a precursor of the vertebral column, not of the brain.
• is a kind of fruit. The notochord is a rod-shaped structure in animals.
• acts as a precursor for the development of the vertebral column — correct. Yes!