In this article, we discuss everything there is to know about the phylum chordate. We discuss the distinctive traits that qualify the classification of animals as chordates, and conclude with a list of prominent members of the chordate family.
What animals are in the phylum chordata?
Animals that belong to the phylum chordata include all species of vertebrates and two groups of invertebrates. The vertebrates include: birds, fishes, mammals, amphibians and reptiles, while the invertebrates include: Urochordata (tunicates) and Cephalochordata (lancelets).
The phylum chordata
The phylum chordata is one of the several phylums existing and belonging to the broader group called the Kingdom Animalia.
The phylum itself is named after the longitudinal, flexible and rod shaped structure called the notochord located between the digestive tube and nerve cord of all embryonic stage chordates, and in some species of adults.
The phylum chordate boasts of more than 65,000 vertebrate species half of which are bony fishes belonging to the Osteichthyes class of fishes or Pisces and two clades of invertebrate species
All chordate animals: vertebrates and invertebrates, possess four main characteristics (in at least one lifecycle stage) which are peculiar to the group.
These traits are:
1] All chordates have notochord, otherwise known as column or vertebral column in most adult vertebrates. The notochord is a longitudinal and cartilaginous flexible rod located between the digestive tube and the nerve cord in all embryonic stage chordates and in some species of adults. It develops into a vertebral column in all vertebrates and disappears completely in tunicates. The notochord serves as a skeletal support throughout the entire length of the body of chordates with bones. In chordates which lack bones, muscles work against the notochord to confer locomotion to the animal.
2] All chordates posses a postnatal tail: The postnatal tail is an extension of the body (the notochord and nerve cord) beyond the anus. The tail is made up of skeletal elements and muscles and serves as a means of locomotion in aquatic species such as fishes and whales. In some species such as the kangaroos, the tail helps them balance their entire body weight while in other species, the tail helps in courtship and signaling danger. In humans and other species such as frogs, the tail is vestigial, meaning it’s non-functional, and it’s very reduced in size, almost or completely inconspicuous.
3] All chordates posses a dorsal nerve chord: The dorsal nerve chord is a hollow tube dorsal or longitudinal to the notochord. This means that it is located above the notochord. It is present in the embryo stages of most chordates and then develops into a brain and spinal chord, collectively known as the central nervous system in the adult stage. In non-chordates, such as annelids (eg. snails) and arthropods (the spider family), the position of the dorsal nerve chord is ventral or lateral.
4] All chordates posses a pharyngeal silts: The pharyngeal slits are series of openings between the throat (pharynx) and the outside. In primitive chordates, the pharyngeal slits are used to filter food particles. In fishes and amphibians, the slits form gills which are used for gaseous exchange. In terrestrial chordates like humans, the pharyngeal slits is only present in the embryonic stage.
The family tree of chordates
All animals are divided into two groups based on their patterns of embryonic development. The protostomes and the dueterostomes. All of the members of these two groups are bilaterally symmetrical.
Bilaterally symmetrical means that the organisms have body shapes that are mirror images of one another along a midline called the sagittal plane. The internal organs, however, are not necessarily distributed symmetrically. Humans are perfect examples, both their left sides and right sides are perfect mirror images of one another.
In protostomes, the sister clade to dueterostomes, the mouth forms before the anus during the embryonic development stage, whereas in dueterostomes, reverse is the case, the anus forms first.
Under dueterostomes, three phyla or groups exist, they include:
Chordata, the group we are most interested in, consist of members that are referred to as chordates. Most of the members are vertebrate animals (animals posseing a backbone in their adult stages), except for the invertebrates, the tunicates and lancelets clade of invertebrates. More appropirately, we can say that the phylum chordata is sub divided into three sub-phyla which are:
- Cephalochordata (tunicates)
The family tree of chordates
Hemichordate (which includes the acorn worms) was once classified as the fourth member group under the phylum chordata, but modern revisions have now drafted it under the phylum ambulacraria which also includes the echindermata. Ambulacraria now forms the sister phylum of chordates.
Based on all the information above, the defining characteristic of all chordates can be weakly extended to include two more traits which are.
- All chordates are billaterally symmetrical
- All chordates are members of the dueterostomes group, or have their anus formed first before their mouth during their embryonic development stage.
Members of the phylum chordata
a) Vertebrates: this group is further divided into five classes namely:
- Birds: Examples include, vultures and chickens.
- Mammals: Examples include, humans and felids.
- Fishes: Examples include, sharks and mackerel fish.
- Reptiles: Examples include, snakes, lizards and crocodiles.
- Amphibians: Examples include, toads, frogs.
To understand more about how organisms are grouped, read under the subheading “is fish an animal?” in this article: is fish an animal?
b) Invertebrates: two groups namely Urochordata (tunicates) and Cephalochordata (lancelets) exists.
- Urochordata: These are invertebrates that can take either the form of sea squirt or salps as adults. At this stage, the adult stage, they lack the four standard features that define chordates, but in their embryonic stages, all the features are present. Urochordata have soft bodies and are filter-feeders that feed primarily on planktons.
- Cephalochordata: These are marine invertebrates that are widely recognized as burrowing filter-feeders. They vaguely look like fishes and are small, lack brains (in embryo-hood and adulthood), clearly defined heads and specialized sense organs.
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Cite this Article ” (APA Format)
Bunu. M. (2020, May 30). What animals are in the phylum chordata?. Retrieved from http://emborawild.com/animals-in-phylum-chordata/