Section 33-3: Exploring Form And Function In Chordates

Last Modified: Published: 2023/05
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Chordates are a diverse group of animals that includes vertebrates and some invertebrates. They are known for their notochord, a flexible rod-like structure that runs the length of their body. In this article, we will explore the form and function of chordates in Section 33-3 of our biology textbook.

The Evolution of Chordates

The earliest chordates were marine animals that lived over 500 million years ago. They were small, filter-feeding animals that resembled modern-day lancelets. Over time, chordates evolved into more complex animals, including fish, amphibians, reptiles, birds, and mammals.

Chordate Anatomy

All chordates have a notochord, which provides support and allows for movement. In vertebrates, the notochord is replaced by the vertebral column. Chordates also have a dorsal nerve cord, which runs along their back, and pharyngeal slits, which are used for feeding and gas exchange.

The Function of Chordate Features

The notochord provides support for the body and allows for movement, while the dorsal nerve cord serves as the main pathway for communication between the brain and the rest of the body. Pharyngeal slits are used for feeding and gas exchange in aquatic animals and are modified for other functions in terrestrial animals.

Chordate Classification

Chordates are classified based on their features, including the presence of a backbone, the type of jaw, and the presence of limbs. The three main groups of chordates are fish, amphibians, and reptiles/birds/mammals.


Fish are aquatic animals with gills and fins. They are classified into three groups: jawless fish, cartilaginous fish, and bony fish. Jawless fish include lampreys and hagfish, while cartilaginous fish include sharks and rays. Bony fish include both ray-finned and lobe-finned fish.


Amphibians are animals that live both on land and in water. They are classified into three groups: frogs/toads, salamanders/newts, and caecilians. Amphibians are known for their ability to breathe through their skin and for undergoing metamorphosis.


Reptiles, birds, and mammals are all classified together because they share certain characteristics, including amniotic eggs and a four-chambered heart. Reptiles include snakes, lizards, and turtles, while birds are known for their feathers and ability to fly. Mammals are characterized by their hair/fur and ability to produce milk for their young.


Chordates are a diverse group of animals that have evolved over millions of years. They are known for their notochord, dorsal nerve cord, and pharyngeal slits. Chordates are classified into three main groups: fish, amphibians, and reptiles/birds/mammals. By understanding the form and function of chordates, we can better appreciate the diversity of life on Earth.



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