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What's a Phylum?

Samantha Savage Grace, Jeffrey Sack
  • Author
    Samantha Savage Grace

    Samantha has taught science, mathematics, and engineering for over 5 years. They have a Master's in the Art of Teaching with a focus in inclusive and equitable STEM education from Goucher College and a Bachelor's in Biology from University of Maryland Baltimore County with minors in Psychology and Emergency Health Services. In addition to teaching licenses in multiple disciplines they also hold certifications through Project Lead the Way for engineering and are AVID certified.

  • Instructor
    Jeffrey Sack

    Jeff is a Biology teacher and has a Doctorate in Educational Leadership

In this lesson, see the definition of a phylum and how phylum classification is organized. Understand some reasons why organisms are put into different phyla. Updated: 07/25/2021

What is a Phylum?

Human beings have always had a desire to organize and classify the world around them. What was once the work of ancient philosophers, now is its own branch of scientific inquiry. Taxonomy is the scientific discipline whose goal it is to classify and organize living things based on their characteristics and ancestry. The most widely used classification system is the taxonomic rank developed primarily by Carl Linnaeus. This hierarchical system divides the living world into progressively smaller and more specific groups. From broadest classification to most specific, the system is divided as follows:

  • Domain: The broadest and most recently added taxonomy group, it divides organisms into Bacteria, Archaea, and Eukaryota
  • Kingdom: The second most broad level of classification, it divides living things into the groups Animalia, Plantae, Fungi, Protista, Archaea, and Bacteria. However, this classification group is the source of much debate and revision as it's often considered inaccurate.
  • Phylum: The third most broad taxonomical group which further divides organisms based on their morphological characteristics or evolutionary relatedness.
  • Class: This is the fourth most broad taxonomical group which divides organisms based on a shared feature. This was the broadest category proposed by Linnaeus, but it is not often used by botanists due to modern findings rendering it less accurate.
  • Order: Order is the fifth taxonomical group and further subdivides organisms, there is no agreed upon rationale for placing organisms into different orders.
  • Family: This is the sixth taxonomical group where organisms are further subdivided, it again is decided at the taxonomist's discretion.
  • Genus: This is the seventh taxonomical group and is a specific collection of organisms and the first part of an organism's scientific name.
  • Species: This is the eighth and final taxonomical group, it is the most specific of the taxonomical classifications.

Binomial nomenclature is the process of assigning organisms a scientific name using both it's genus and species. When written out the genus always comes first and is always capitalized, while the species is always second and is always lowercase. When writing an organism's scientific name both the genus and species are always italicized, for example the scientific name for polar bear is written as Ursus maritimus. Ursus is the genus, while maritimus is the species. When an organism is referred to repeatedly in the same paper the genus may be abbreviated, for example Ursus maritimus may be shortened to U. maritimus.

What Is a Phylum?

The living world is very diverse. There are millions of different organisms that have been discovered, and it is estimated there are millions more yet to be found. If science did not have some kind of organized way of keeping track of all these critters, it would be very difficult to conduct any research, and information about particular creatures would never pass around the scientific community.

Just like books in the library, living things are grouped according to similar characteristics. These may be physical, behavioral, or genetic. Phylum is one of the eight major categories that can be used to organize the relationships between organisms. In order, they are: domain, kingdom, phylum, class, order, family, genus, and species.

In Ancient Greece, a man named Aristotle was one of the first to classify organisms. He put all living things within two main groups - plants and animals. He then put each of these into a smaller group depending upon where the creature lived.

It wasn't until the 18th century, when a botanist named Carl von Linné developed a system still used today. He was frustrated by the fact that some organisms had several descriptive names and others had none. He also realized that certain organisms are found all over the world, which caused them to have multiple common names. So Linné designed a system using Latin names that removed the confusion. He assigned a hierarchical classification scheme for all living things that gave each organism a two-word Latin name that was unique to it. This system of classification is called binomial nomenclature.

Taxonomy is the classification of organisms. The advent of genetic technology and DNA fingerprinting has allowed for a much more accurate and complete analysis of how organisms are related. Modern taxonomists have found that organisms that were once thought to be related are not connected at all, and others that show no external similarities are actually very similar genetically.

There are over 30 animal phyla. Let's go over some examples.

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  • 0:30 Definition
  • 1:35 Binomial Nomenclature
  • 2:29 Example Phylum: Chordata
  • 3:42 Example Phylum: Arthropoda
  • 4:32 Example Phylum: Echinodermata
  • 5:35 Plant Phyla
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Phylum Classification?

Taxonomical groups become progressively specific as they move from domain to species. Each level is further subdivided based upon characteristics and features shared by members of the group. Organisms are classified into their respective phylum based on shared morphological features or evolutionary relatedness. The Bacteria phylum Aquificae are all hyperthermophilic bacteria that live in areas with extreme high temperatures. Mollusca are a phylum of Animalia, grouped together due to all members being invertebrates with distinct areas for their head and feet. The kingdom Archaea has only two phylums, Euryarchaeota and Crenarchaeota which are divided based on rNA sequences and their DNA polymerase. In the kingdom of Plantae the phylum Angiospermophyta are all organisms who use flowers to reproduce while the phylum Coniferophyta are all evergreens.

Phylum Examples

The kingdom Animalia can be further organized into seven phyla: Porifera, Cnidaria, Platyhelminthes, Annelida, Arthropoda, Chordata, and Mollusca.

Example Phylum: Chordata

You are a member of a phylum Chordata. It contains all of the vertebrate animals (fish, birds, reptiles, amphibians, and mammals), as well as a couple of invertebrate ones. All members of this phylum have certain structures, though sometimes they only show up during the embryo phase.

These structures include: pharyngeal slits- a series of openings in the throat connecting to the outside of the 'neck'. These are often, but not always, used as gills.

A dorsal nerve cord- a bundle of nerve fibers that runs down the top of the animal. It connects the brain with the muscles and other organs.

A notochord- a cartilaginous rod running underneath and supporting the nerve cord.

A post-anal tail- an extension of the body past the anal opening.

Ancestral Chordate
Ancient Chordate

There are a couple of organisms in this phylum that are invertebrates. One such creature is called the sea squirt, marine organisms that are very good at filtering water. They create a current of water using a tube called a siphon. Inside of the animal's body is mesh-like tissue that filters out plankton.

Sea Squirt
Sea squirt

Example Phylum: Arthopoda

The phylum Arthropoda is the largest animal phylum. It contains all the insects, crabs, lobsters, spiders, and scorpions. It is believed there are more than one million types of insects alone on the planet, with many of them yet undiscovered.

General characteristics of arthropods include jointed legs and an exoskeleton. The exoskeleton offers protection to the animal but does not grow with it. When the animal gets too large for the exoskeleton, it needs to shed it and then grow a new one. As it climbs out of its old shell, its body is very soft. It will harden up over time. The exoskeleton breaking is the crunching sound you hear when you step on a bug or crack open a lobster.

Lobster - Phylum Arthropoda
Lobster meal

Example Phylum: Echinodermata

The phylum Echinodermata contains those animals with a 'spiny skin.' The animals in this phylum are the sea stars, sea urchins, bristle stars, sand dollars, and sea cucumbers.

Sea Cucumber - Phylum Echinodermata
Sea Cucumber

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Video Transcript

What Is a Phylum?

The living world is very diverse. There are millions of different organisms that have been discovered, and it is estimated there are millions more yet to be found. If science did not have some kind of organized way of keeping track of all these critters, it would be very difficult to conduct any research, and information about particular creatures would never pass around the scientific community.

Just like books in the library, living things are grouped according to similar characteristics. These may be physical, behavioral, or genetic. Phylum is one of the eight major categories that can be used to organize the relationships between organisms. In order, they are: domain, kingdom, phylum, class, order, family, genus, and species.

In Ancient Greece, a man named Aristotle was one of the first to classify organisms. He put all living things within two main groups - plants and animals. He then put each of these into a smaller group depending upon where the creature lived.

It wasn't until the 18th century, when a botanist named Carl von Linné developed a system still used today. He was frustrated by the fact that some organisms had several descriptive names and others had none. He also realized that certain organisms are found all over the world, which caused them to have multiple common names. So Linné designed a system using Latin names that removed the confusion. He assigned a hierarchical classification scheme for all living things that gave each organism a two-word Latin name that was unique to it. This system of classification is called binomial nomenclature.

Taxonomy is the classification of organisms. The advent of genetic technology and DNA fingerprinting has allowed for a much more accurate and complete analysis of how organisms are related. Modern taxonomists have found that organisms that were once thought to be related are not connected at all, and others that show no external similarities are actually very similar genetically.

There are over 30 animal phyla. Let's go over some examples.

Example Phylum: Chordata

You are a member of a phylum Chordata. It contains all of the vertebrate animals (fish, birds, reptiles, amphibians, and mammals), as well as a couple of invertebrate ones. All members of this phylum have certain structures, though sometimes they only show up during the embryo phase.

These structures include: pharyngeal slits- a series of openings in the throat connecting to the outside of the 'neck'. These are often, but not always, used as gills.

A dorsal nerve cord- a bundle of nerve fibers that runs down the top of the animal. It connects the brain with the muscles and other organs.

A notochord- a cartilaginous rod running underneath and supporting the nerve cord.

A post-anal tail- an extension of the body past the anal opening.

Ancestral Chordate
Ancient Chordate

There are a couple of organisms in this phylum that are invertebrates. One such creature is called the sea squirt, marine organisms that are very good at filtering water. They create a current of water using a tube called a siphon. Inside of the animal's body is mesh-like tissue that filters out plankton.

Sea Squirt
Sea squirt

Example Phylum: Arthopoda

The phylum Arthropoda is the largest animal phylum. It contains all the insects, crabs, lobsters, spiders, and scorpions. It is believed there are more than one million types of insects alone on the planet, with many of them yet undiscovered.

General characteristics of arthropods include jointed legs and an exoskeleton. The exoskeleton offers protection to the animal but does not grow with it. When the animal gets too large for the exoskeleton, it needs to shed it and then grow a new one. As it climbs out of its old shell, its body is very soft. It will harden up over time. The exoskeleton breaking is the crunching sound you hear when you step on a bug or crack open a lobster.

Lobster - Phylum Arthropoda
Lobster meal

Example Phylum: Echinodermata

The phylum Echinodermata contains those animals with a 'spiny skin.' The animals in this phylum are the sea stars, sea urchins, bristle stars, sand dollars, and sea cucumbers.

Sea Cucumber - Phylum Echinodermata
Sea Cucumber

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Frequently Asked Questions

What is the term phylum?

The term phylum refers to the third most broad category of taxonomical hierarchy. This level comes after kingdom, but before class. Organisms are sorted in this level based on shared morphological features and/or shared ancestry.

What is an example of a phylum?

A phylum is the third most broad category of taxonomy, falling between kingdom and class. One example of a phylum is Chordata, a phylum of the kingdom Animalia. This group of organisms all have a notocord and almost all have a backbone.

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