Phylum Chordata – Definition, Characteristics, Classes

Phylum Chordata Definition

“The chordates are a class of animals that have four anatomical characteristics, which are (1) nochord (2) dorsal cord of nerves, (3) post-anal tail and (4) Pharyngeal slits, at the very least, during a portion of their growth into maturity.”

Or

A phylum within the animal kingdom, which includes all animals that have at least one time in their lives, a noochord (a hollow nerve) and pharyngeal slits along with a tail of muscle that extends beyond the anus. It includes three subphylas: Cephalochordata, Urochordata, and Vertebrata (vertebrates). 

Etymology: comes from Latin chorda, which means “cord”, “string”. Synonym: chordate.

• Chordata belongs to the phylum that comprises the animal kingdom, which includes an array of animals, including humans.
• Animals in the Phylum Chordata include all animals with an ochord, at least at some point in their lives.
• A phylum is a classification that is ranked third after kingdom and domain within the order of classification. The organisms that belong to a phylum share characteristics that distinguish them from other organisms belonging to another phylum.
• Chordata is a family of animals which includes vertebrates as well in sea squirts and lancelets. Many well-known vertebrates like reptiles, fishes and mammals and amphibians are found within the family of Chordata.
• The word “chordate” is used to describe any animal that belongs to the phylum Chordata. 

General features of Phylum Chordata

Vertebrates are an euchordate, possess post-anal tails and a notochord. They also have the pharyngeal slits and a dorsal hollow nerve. However, their notochord evolves into a spine. This is a bony column vertebrae that are separated by discs. Other common characteristics of chordates in vertebrates include:

• Bilateral symmetry
• Segmented body
• A fully developed and fully functioning coelom
• A huge anterior brain end with an empty dorsal single nerve cord
• The extension of tail well over the Anus in any stage
• The existence of pouches for the pharyngeal region.
• A ventral heart
• The closed system of blood supply.
• Dorsal and Ventral blood vessels.
• The possibility of having an entire digestive system.
• The existence of cartilaginous and bony systems of the endoskeleton.

Pandas, crows salamanders, alligators sea squirts and many more are all examples of chordates. In essence in order for the purpose of answering: reptiles, amphibians, and mammals are part of the same group? The answer is simple: they are all part of the Chordata phylum. Chordata. What about humans… are we chordates? Yes, we are chordates. At some stage the human embryo creates an onotochord. It will eventually transform into a vertebral column in particular when the embryo is developing into an embryo. Like we said the animal with a notochord at some point in its life is deemed as a chordate.

Characteristics of Phylum Chordata

Animals that belong to this phylum share four essential characteristics: a notochord dorsal hollow nerve cordand pharyngeal openings, and the post-anal tail. We will discuss each of them below.

a. Notochord

• It is rod with a flexible structure which is located on the anteroposterior axis (i.e. from top to the bottom) of the body of organisms. It is located dorsal to the gut and ventral the central nervous system of the body.
• The notochord is, as a matter of fact, the place from which the chordates got their names. The rod-shaped and flexible structure can appear at any stage of development in the chordate or even persist into adulthood.
• The chordates with a notochord that lasts for their entire lives, utilize it for an skeletal support. Other chordates for instance vertebrates the notochord is replaced by a vertebral column (spine) beyond the stage of embryogenesis.
• The notochord is located between the intestinal tube and nerve code. It plays a major role in signaling , and in vertebrates, plays an important role in coordinating growth as well as development. Particularly the vertebrate noochord triggers neural tube growth. This process is termed notogenesis.

b. The dorsal hollow nerve cord

• The dorsal hollow cord is a hollow tube that originates from the ectoderm at the embryonic stage in vertebrates. It lies in the dorsal region of the notochord. This is why it can be found in the middle of the notochord when chordates are being performed.
• This tube is composed of nerve fibers that eventually develop into the nervous system central, where the brain as well as the spinal cord comprise the major constituents.
• The dorsal hollow nerve can be protected from vertebral columns.
• It is important to note that the nerve, however it is not a unique characteristic of chordates. It’s also found in other phyla of animals.
• In some animals, it’s located either laterally or ventral in contrast to chordates that are located between the notochord and the ventral.

c. Pharyngeal slit

• The pharynx’s openings, i.e. the area below the mouth (or the oral cavities) and extends outwards to the outside (environment) are referred to as the slits of the pharynx. These slits are utilized by the chordates of invertebrates to filter feed. The mouth is filled with water to filter food particles, and the water leaves through the slits of the pharyngeal passages.
• In aquatic vertebrates like fish, Pharyngeal slits can be transformed into gill supports, or Jaw supports (as for the jawed fishes).
• For vertebrates other than vertebrates like birds and mammals The pharyngeal openings are present in the time of embryogenesis. They then are incorporated into the tonsils and the ear.

d. Post-anal tail

• The posterior extension of the body which goes beyond anus is known as the post-anal tail.
• In aquatic chordates the post-anal portion of the tail contains muscles and skeletal elements, which are vital to the organism’s movement within the aquatic environment. By definition, locomotion is the capacity for an animal to travel from one spot to another.
• Jumping, swimming, running in the air, flying and hopping are just a few examples of locomotion in animals.
• In this respect the post-anal tail has an important role in facilitating fishes to move around for example.
• In terrestrial chordates the tail is employed to balance and for signaling.
• Humans and other apes this tail is considered to be a vestigial part which means it is present during the development of embryos but it shrinks or disappears at the time of birth.

Reproduction and Life Cycle of Phylum Chordata

• The entire new and diverse class of vertebrates comprising the vertebral column, tunicates and lancelets is represented in the phylum Chordata. Two methods are employed for the reproduction of sexually transmitted eggs: (1) internal fertilization and (2) external fertilization.
• Through in-vitro fertilization process, the sperm as well as the eggs (collectively called the gametes) join within the body.
• External fertilization occurs when the sperm fertilizes eggs outside of the body. thus, this type of fertilization is restricted to aquatic species.
• The subphylum Cephalochordata is a number of tiny species of lancelets which are tiny fish-like creatures with a nerve cord which can be supported by the noochord, instead of spine. In the season of mating the males and females both produce eggs and sperms, which are released simultaneously to fertilize. During the spawningprocess, the gametes are flushed into the water through eventually breaking gonads. The subphyla Urochordata and Vertebrata reproduction could be sexual or anasexual.
• In fish, reproduction takes place via external fertilization, in which numerous gametes released by males as well as females to ensure a successful reproduction. In the same way, amphibians reproduce by external fertilization. Females and males usually meet at an area of breeding (a pool or well in an area of). Females deposit numerous eggs, while males deposit many fertilized sperms.

A diagram that illustrates the life-cycle of different chordates is provided below.

Phylogeny of Phylum Chordates

• It is possible to identify three Chordata subphylas i.e. Urochordata (Tunicata), Cephalochordata as well as Vertebrata (Craniata).
• The most prominent features that each of the three classes are classified are the notochord, nerve cord endostyle, branchial slits postanal tail and a myotome.
• Chordata is now part of the superphyletic Deuterostomia together with the other phylums Hemichordata along with Echinodermata.
• The common ancestor that the chordates evolved are called deuterostomes. So, the majority scientists believe that, of all three phyla of chordates, the initial one to evolve was Urochordata which was followed by Cephalochordata and then Vertebrata.
• The term”protochordate” is extensively employed to describe the chordate phylogeny. The in-depth analysis of classic reviews on the phylogeny and evolution of chordates has been outlined in the image below. However there are many queries that are often on readers’ minds about the development of chordates. It has been observed that an acceptable answer to these questions can be easily provided by using molecular phylogeny.
• The broad classification of this area of science has enabled scientists to change the classification of the metazoan groups at the level of phylum. Protostomes and deuterostomes were conventional categories within which the Bilaterians and triloblasts were classified.
• The protostomes were split into acoelomates Platyhelminthes and pseudocoelomates. They were according to the ways in which they formed different formations within the body’s cavity.
• These categories did not have the support of the molecular phylogeny , but rather on the basis DNA sequences and sequences of proteins in the gene-coding.
• The protostomes are again split into two main groups: Lophotrochozoa as well as Ecdysozoa. A clade has been created from the echinoderms as well as the hemichordates. Another one is made by vertebrates, urochordates and cephalochordates. This is confirmed by findings from molecular phylogeny and mitochondrial nuclear biology. Therefore, it is conclusively concluded that the first Clade is an Ambulacraria phylum. Ambulacraria and the second is that it is the Chordata phylum.
• In addition there is Chordata Cephalochordates were the first to emerge and the two other groups, urochordates and vertebrates, form an identical class. The most recent look at the phylogeny and phylogeny of chordates has been presented in the following image.

Classes of Phylum Chordata

Phylum Chordata is divided into three subphylas:

1. Urochordata (tunicates),
2. Cephalochordata (lancelets)
3. Vertebrata (vertebrates).

Subphylum Urochordata along with Cephalochordata are collectively referred to as protochordates. These are marine mammals. They are invertebrates, but they have the characteristics of chordates.

Urochordata

• The adults are attached to the substratum.
• It’s also known as Tunicate since the adult’s body is enclosed in the tunic, which is made of cellulose, a substance that is also known as tunicin.
• Notochords are only visible during the larval stage, and disappears when adults are born.
• The nerve that is present in the larva gets replaced by a dorsal-ganglion in adults.
• The larva moves and undergo a metamorphosis.
• For e.g., Ascidia, Salpa, Doliolum.

Cephalochordata

• The atrium is visible.
• The larval stage and the adult stage are both motile.
• The tail is present all through the course of.
• They display the progression of metamorphosis.
• The notochord can be found in all aspects of all of.
• Many well-developed pharyngeal gill openings are found.
• For e.g., Lancelets possess the nerve cord and notochord throughout their lives. However, they don’t have bone vertebral columns and brains similar to Branchiostoma.

Vertebrata

The distinctive features of vertebrates are:

• They are advanced chordates and contain craniums around the brain.
• The notochord is replaced with the vertebral column in adulthood. This is the reason why it’s claimed that all vertebrates are chordates, but all chordates aren’t vertebrates’.
• A high level of cephalization can be observed.
• The epidermis has multiple layers.
• They are composed of three kinds of muscles: unstriped, stripes and cardiac.
• They have a developed coelom.
• The alimentary canal has been made completely complete.
• The heart is a three-chambered or four-chambered.
• They have developed respiratory and excretory systems.
• The glands for hormones are found throughout.
• They are unisexual, and reproduce sexually, with the exception of hagfish. the exception.
• For e.g., humans.

Subphylum Vertebrata It is also divided into 7 classes. They include:

• Cyclostomata
• Chondrichthyes
• Osteichthyes
• Amphibia
• Reptilia
• Aves
• Mammalia

Ecological Importance of Phylum Chordata

• The chordates play an extremely important role in maintaining an equilibrium in our ecological system.
• The amphibians play an extremely important part in the ecology of wetlands through preying on insects, eating algae and dead plants that can be found in streams and ponds.
• They can be a good indicator of the state of health in the environment.
• The other chordates are the primary source of human food. These include fishes as well as various other animals that may be hunted. There are also other mammals who live in our house as pets, and help us with our everyday tasks. Their function and influence on the ecosystem are huge.

Examples of Chordata Phylum Chordata

There are many examples of Chordata because it is among the numerous phylas in our world like:

Lampreys

• Lamprey, for example, is a vertebrate that belongs to the subphylum Vertebrata.
• It is a jawless fish that can be seen living on feeds that are filtered and then grown to an adult who has an oral disk with teeth sharp enough to bind fish (to get food).
• Their body is made up of gills to breathe and a skeleton comprised by cartilage noochord and a nerve cord. Mucus-secreting organs are used to collect food particles.

Sea Squirt

• They are tunicates with bodies that is barrel-shaped and attached to the substrate.
• These adults filter feeders that use special structures known as siphons.