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Chordates vs. Protochordates: What's the Difference?

By Janet White || Updated on November 22, 2023
Chordates are animals with a notochord at some stage, whereas protochordates are simpler, lacking a true backbone.

Key Differences

Chordates are a broad group of animals that, at some stage in their development, possess a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail. Protochordates, on the other hand, represent a sub-category of chordates that exhibit these features in a more primitive form and lack a true vertebral column.
The diversity among chordates is vast, ranging from fish to mammals, all sharing key developmental patterns. Protochordates, such as tunicates and lancelets, serve as a crucial link in understanding the evolution of chordates, demonstrating basic structural plans without developing into complex vertebrates.
In chordates, the notochord usually develops into a complex, segmented spine, a hallmark of vertebrates. Protochordates, in contrast, maintain the notochord throughout their lives as a simple, unsegmented rod, indicating their more basal position in the chordate lineage.
Chordates exhibit a high degree of developmental complexity, including intricate organ systems. Protochordates, while sharing the fundamental chordate plan, show much simpler anatomical structures, lacking the advanced systems found in higher chordates.
The study of chordates encompasses a wide range of animals from simple fish to humans, focusing on their shared evolutionary traits. Protochordates provide essential insights into the early stages of chordate evolution, offering a glimpse into the ancestral traits of this diverse group.

Comparison Chart


Possess a developed backbone or vertebral column
Lack a true backbone; have a notochord instead


Exhibit complex organ systems and higher body organization
Simpler body structures and organ systems

Evolutionary Stage

More advanced in the evolutionary timeline
Primitive, representing early chordate development


Include fish, amphibians, reptiles, birds, mammals
Mainly tunicates and lancelets


Notochord develops into spine in most
Notochord remains throughout life

Chordates and Protochordates Definitions


Chordates are characterized by having bilateral symmetry and a coelom.
Fish, with their bilateral symmetry, are classified as chordates.


Protochordates are primarily characterized by having a notochord throughout their life.
Tunicates, despite their simplicity, are considered protochordates due to their notochord.


Chordates are notable for their post-anal tail, which extends beyond the anus at some stage.
The embryonic development of a kangaroo shows a post-anal tail, a defining feature of chordates.


Protochordates show basic features of chordates but do not develop into complex vertebrates.
Sea squirts, living attached to rocks, are protochordates that exhibit basic chordate features.


Chordates are animals that at some point in their life cycle have a notochord, a dorsal hollow nerve cord, and pharyngeal slits.
Humans are chordates because they have these features during their embryonic development.


Protochordates are important for understanding the evolutionary link between invertebrates and vertebrates.
The study of amphioxus, a protochordate, helps scientists understand vertebrate origins.


In chordates, the notochord provides skeletal support, a feature seen in various forms across the group.
The presence of a spinal column in dogs is an evolution of the notochord, typical of chordates.


Protochordates are a subgroup of chordates that display primitive characteristics, lacking a true backbone.
Lancelets, as simple marine animals, are classic examples of protochordates.


Chordates encompass a vast group of animals ranging from simple sea creatures to complex mammals.
Birds, as diverse as they are, fall under the category of chordates.


Protochordates lack the advanced organ systems seen in higher chordates.
Cephalochordates, a group of protochordates, have simple body plans compared to more advanced chordates.


Any of numerous animals of the phylum Chordata, having at some stage of development a dorsal nerve cord, a notochord, and gill slits and including all vertebrates, the hagfishes, and certain marine animals such as the lancelets and the tunicates.


Plural of protochordate


Plural of chordate


Are humans considered chordates?

Yes, humans are chordates because they exhibit all the defining features during embryonic development.

What are protochordates?

Protochordates are a subgroup of chordates that retain primitive features and lack a true backbone.

How do protochordates differ from other chordates?

Protochordates are simpler, lacking complex organ systems and a developed backbone, unlike other chordates.

Are all fish considered chordates?

Yes, all fish, whether cartilaginous or bony, are classified as chordates.

Is the nervous system of protochordates complex?

Protochordates have a simpler nervous system compared to more advanced chordates.

Do protochordates have a heart?

Some protochordates have simple circulatory structures, but not a true heart as seen in higher chordates.

What defines a chordate?

Chordates are defined by having a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail at some life stage.

Can protochordates be found on land?

No, protochordates like tunicates and lancelets are exclusively marine animals.

Do chordates all have a similar life cycle?

While chordates share key developmental stages, their life cycles can vary greatly, from simple to complex.

Do all chordates have a backbone?

No, not all chordates have a backbone; protochordates, for example, do not develop a true vertebral column.

Do chordates always have a notochord throughout their life?

In many chordates, the notochord is replaced by a vertebral column during development.

How are chordates important in evolutionary studies?

Chordates are crucial for understanding the evolution of complex organ systems and vertebrates.

Are protochordates considered ancestors of vertebrates?

Protochordates are not direct ancestors but provide insights into the early evolutionary stages of vertebrates.

Do protochordates have lungs or gills?

Protochordates generally use their body surface or simple structures for gas exchange, not lungs or gills.

What role does the notochord play in protochordates?

In protochordates, the notochord serves as the main axial support structure throughout their life.

Are all chordates vertebrates?

No, not all chordates are vertebrates; protochordates are chordates without a vertebral column.

Can protochordates reproduce on land?

No, protochordates are marine animals and their reproduction is tied to aquatic environments.

Are birds classified as chordates?

Yes, birds, with their vertebral column and other chordate features, are classified as chordates.

How do chordates differ in their reproductive methods?

Chordates exhibit a wide range of reproductive methods, from simple spawning to complex live births.

Do protochordates play a role in marine ecosystems?

Yes, protochordates, like tunicates, play significant roles in marine food chains and ecosystem dynamics.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.

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