Table of Contents
What is Chordata?
Chordata is an animal kingdom phylum that comprises a diverse range of animals, including humans, and all creatures that have a notochord at some point in their lives belong to the Phylum Chordata.
A Phylum is a taxonomic classification that follows third in the hierarchy of classification after domain and kingdom. Creatures belonging to the same phylum possess similar features that distinguish them from organisms belonging to different phyla.
Chordata is a vast class of creatures that includes vertebrates, lancelets, and sea squirts, among others, and it includes several well-known vertebrates, such as reptiles, fishes, mammals, and amphibians.
What are Chordates?
Any animal belonging to the phylum Chordata is referred to as a “chordate.” “The chordates are the class of animals that, at least throughout some part of their development into adulthood, have four anatomical characteristics, namely;
(2) Dorsal nerve cord
(3) Post-anal tail
(4) Pharyngeal slits
a phylum of the animal world that includes all creatures with a notochord (a hollow dorsal nerve cord), pharyngeal slits, and a muscular tail reaching past the anus at some point in their lives. The subphyla Cephalochordata, Urochordata, and Vertebrata are included (vertebrates). From the Latin chorda, which means “cord” or “string.” chordate is a synonym for chordate.
Is it true that all chordates are vertebrates?
Chordates encompass all vertebrates. Not all chordates, however, are vertebrates.
Vertebrates have a post-anal tail, a notochord, pharyngeal slits, and a dorsal hollow nerve cord because they are chordates. Their notochord, on the other hand, develops into a spine, a column of bone vertebrae divided by discs.
Other common characteristics of chordates found in vertebrates include:
• Symmetry on all sides.
• Body with segments
• The firm’s full potential has been realized.
• A single nerve cord has a hollow dorsal end and a big anterior brain end.
• At any stage of growth, the tail projects far beyond the anus.
• There are pharyngeal pouches.
• A heart with a ventral location.
• A blood system that is completely closed.
• Blood vessels in the ventral and dorsal areas.
• A whole digestive system is available.
• Endoskeleton systems are cartilaginous and bony.
Chordates include pandas, crows, sharks, salamanders, alligators, sea squirts, and many others. So, to answer the question, which phylum contains amphibians, reptiles, and mammals, the answer is Chordata.
What about people... Are we chordates as a species?
Humans, too, are chordates. The human embryo generates a notochord, which eventually develops into a vertebral column, especially when the embryo develops into a baby. Any animal with a notochord at any time in its existence is called a chordate, as previously stated.
A notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail are all characteristics shared by animals in this phylum.
The notochord is a flexible rod that runs down the organism’s body’s anteroposterior axis (from top to bottom) and is located dorsal to the stomach and ventral to the body’s central nervous system.
In reality, the chordates get their name from the notochord. This flexible, rod-shaped structure can arise at any time throughout chordate development and can even last until maturity.
Chordates with a notochord that lasts their entire lives use it for skeletal stability. The notochord is replaced by a vertebral column (spine) in other chordates, such as vertebrates, after the embryonic period.
Between the nerve code and the stomach tube is the notochord, which plays a crucial function in coordinating growth and development in vertebrates and is largely engaged in signalling.
The notochord of vertebrates, in particular, stimulates neural tube growth. The process of development is known as notogenesis.
ii. The Dorsal Hallow Nerve Cord
The dorsal hollow nerve cord is a hollow tube generated from the ectoderm and positioned posterior to the notochord during the embryonic stage of vertebrates.
In chordates, it may be observed near the top of the notochord. This tube is made up of nerve fibres that eventually grow into the central nervous system, which consists mostly of the brain and spinal cord. The vertebral column protects the dorsal hollow nerve cord.
The nerve cord, on the other hand, is not exclusive to chordates. Other animal phyla have it as well. In other species, it is ventral or laterally situated, as opposed to chordates, where it is dorsal to the notochord.
iii. Pharyngeal Slits
The pharyngeal slits are the apertures in the pharynx which are located below the mouth (or oral cavity) and extend to the outside (environment). Invertebrate chordates utilise these apertures for filter feeding. As water enters the mouth and leaves through the pharyngeal slits, it filters food particles.
The pharyngeal slits of aquatic animals, such as fish, are eventually converted into gill supports or jaw supports (as in jawed fishes). The pharyngeal slits are present in other animals, such as mammals and birds, at the embryonic stage and eventually integrate as portions of the ear and tonsils.
iv. Post-anal Tail
The post-anal tail is a posterior extension of the body that extends beyond the anus. The post-anal tail of aquatic chordates contains skeletal components and muscles, making it crucial for the organism’s movement in the aquatic environment.
By definition, locomotion refers to an organism’s ability to move from one location to another. Animal locomotion includes activities such as running, swimming, leaping, flying, and hopping. In this sense, the post-anal tail, for example, plays an important function in facilitating fish movement. The tail is utilised for balance and signalling in terrestrial chordates.
v. Reproduction and Life Cycle
The phylum Chordata encompasses the entire new and diversified class of vertebrates with a vertebral column, tunicates, and lancelets. Internal fertilisation and external fertilisation are the two methods employed for sexual reproduction.
The sperm and eggs (collectively known as the gametes) combine within the body during internal fertilisation. Because the sperm fertilises the egg outside the body in external fertilisation, this type of fertilisation is only found in aquatic creatures.
Many small species of lancelets, which are small fish-like organisms with a nerve cord supported by the notochord instead of a spine, are found in the Cephalochordata subphylum.
Males and females generate sperm and eggs, which are released at the same time for fertilisation during the mating season. The gametes are expelled into the water during spawning when the gonads eventually burst. Sexual or asexual reproduction is possible in the subphyla Urochordata and Vertebrata.
In fish, reproduction happens through external fertilisation, in which males and females release a high quantity of gametes to ensure successful reproduction. Amphibians, too, reproduce by relying on external fertilisation.
The breeding site is where the male and female generally meet (a pond or well of the leaf). Females lay a large quantity of eggs, whereas males lay a large number of sperm.
Evolutionary History of Chordata
The chordates first arose in evolutionary history around 530 million years ago, during the early Cambrian period, when jawless fish fossils first appeared. In 1995, the earliest fossil of the Chordata family was discovered in China, and it was identified as Yunnanozoon lividum.
The researchers estimate that the oldest fossils of tetrapods, mammals, and birds were found roughly 363, 80, and 208 million years ago, based on extensive research on chordate evolution.
The main reason for chordate evolution is large habitat changes, and the earliest chordates documented in the literature were all aquatic species like tunicates and lancelets. As a result of their progressions and evolutions, they eventually made their way to freshwater ponds and ultimately to land.
Many amphibians still choose to dwell in both terrestrial and aquatic settings, demonstrating the intermediary phase in which chordates transition from water to land. In addition, the expansion of the aerial population of birds resulted in a wide spectrum of chordate phylum diversities.
The researchers looked at the chordate’s evolutionary history in depth and came up with four major options, which are the Paedomorphosis theory, the Inversion hypothesis, the Aboral-dorsalization hypothesis, and the Auricularia hypothesis.
The first hypothesis argued whether chordates’ forefathers were free-living or intelligent. Similarly, the remaining three hypotheses shed information on the biology underlying chordate evolution and how they descended from a common ancestor. As a result, all four models are linked, and supporting arguments in each of them may occasionally overlap.
Phylogeny of Chordates
Urochordata (Tunicata), Cephalochordata, and Vertebrata are the three subphyla of Chordata (Craniata). The notochord, nerve cord, branchial slits, endostyle, postanal tail, and myotome are the distinguishing traits that have been used to classify these three types.
Chordata, along with the phyla Hemichordata and Echinodermata, is included in the superphyletic Deuterostomia. The chordates developed from deuterostomes as their common ancestor. As a result, the majority of scientists believe that the Urochordata was the first chordate phyla to emerge, followed by Cephalochordata, and finally Vertebrata.
In the phylogeny of chordates, the term protochordate has been widely used. On the other hand, there are numerous questions that readers frequently have about chordate evolution, and it has been demonstrated that an acceptable solution to all of these issues can be found using molecular phylogeny.
The researchers were able to reclassify the metazoan groups on a phylum level thanks to the broader classification in this field of science. The conventional classifications for Bilaterians and tripoblasts were protostomes and deuterostomes.
Based on the modes of diverse formations in the body cavity, the protostomes were separated into acoelomates, Platyhelminthes, and pseudocoelomates.
The molecular phylogeny did not actively support the indicated groups, instead relying on DNA sequences and protein-coding gene sequences. Lophotrochozoa and Ecdysozoa were used to separate the protostomes into two primary groupings.
The echinoderms and hemichordates have established a clade. The urochordates, vertebrates, and cephalochordates make up another. The data from molecular phylogeny, mitochondrial and nuclear biology have all verified this. As a result, the Ambulacraria phylum is represented by the first clade, whereas the Chordata phylum is represented by the second.
In addition, cephalochordates were the first to develop in Chordata, with the remaining two species, urochordates and vertebrates, forming a sister class.
The phylum Chordata is divided into three subphyla: Urochordata, Cephalochordata, and Vertebrata. Only a few species are classified as Cephalochordata or Urochordata.
Most chordates, such as fish, animals, birds, and reptiles, are members of the Vertebrata (vertebrates) subphylum, with cartilage and bone backbones and a brain enclosed in a hard skull. There are over 50,000 species in this subphylum. They’re everywhere and can be found in a variety of environments, including marine, freshwater, and terrestrial.
Chordata have a unique feature: their bodies are bilaterally symmetric, making them different from other animal phyla. The chordates belong to the deuterostome family. The anus develops in the early embryonic stages before the mouth, which is one of the group’s hallmarks.
Fishes, birds, reptiles, amphibians, and mammals are only a few of the many kinds of vertebrates. Reptiles have scaly, water-resistant skins and are vertebrates which breathe air and lay shelled eggs. They are cold-blooded, which means they can not resist cold temperatures and rely on the temperature of their surroundings to keep their body temperature normal. They have four limbs in most cases. Some of the most frequent reptiles include turtles, chameleons, crocodiles, and snakes.
Amphibians are another well-known chordate group. The term “amphibian” refers to their ability to live in both terrestrial and aquatic environments. They are born in water and have tails and gills, but as they mature into adults, they develop lungs and legs, allowing them to live on land. Reptiles and amphibians have one thing in common: they are both cold-blooded animals, and the class includes frogs, newts, blindworms, salamanders, caecilians, and toads, among others.
The skeleton of chondrichthyes (cartilaginous fish) is made up of cartilage. They have an asymmetrical, upward-curling tail. Chondrichthyes have five to seven different gills on their bodies, and the reproductive cycle is carried out by modified fins that transfer sperm to the females. Rays, skates, sharks, and chimaeras are all members of the Chondrichthyes class. The Agnatha class of chordates, specifically vertebrates, is the oldest known class of chordates (jawless fish). The two main groups of Agnatha are hagifish and lampreys. Hagfishes are specialised scavengers, but lampreys are parasitic fishes that attach to other fishes and feed by sucking their blood.
Warm-blooded animals that make milk in their bodies and use it to feed their young are classified as Mammalia. They have the ability to regulate body temperature in any setting and keep the same temperature throughout their bodies. Their brains are larger than those of other vertebrates. Bears, camels, bats, dolphins, monkeys, and cheetahs are just a few of the most well-known Mammalia animals.
Ecological Importance of Chordata
Chordates play a critical function in maintaining the balance of our biosphere by preying on accessible insects and devouring algae and decaying plants that may flood ponds and streams, amphibians serve a critical role in wetland ecology. Furthermore, they serve as reliable markers of environmental health.
Similarly, the other chordates that are available are the primary source of sustenance for humans. Fish and a variety of other huntable creatures are examples of chordates. In addition, we have a variety of different mammals who live with us as pets and help us with a variety of daily activities. As a result, their utility and impact on our ecosystems are enormous.
As one of the many huge phyla present in our ecosystem, Chordata has many common instances. The lamprey, for example, is a vertebrate belonging to the Vertebrata subphylum. It’s a jawless fish that feeds on filter feeds and grows into an adult with an oral disc covered in sharp teeth that it uses to latch on to other fish (to obtain nourishment). Their bodies are made up of gills for breathing, a cartilage skeleton, a notochord, and a nerve cord. To capture the food particles, a mucus-secreting organ is used.
Sea squirts are another example of Chordata. They’re tunicates with a barrel-shaped body that’s linked to a substrate. Filter feeders, the adults of this species feed using specialised structures called syphons.
The vertebrates, such as bears, camels, bats, dolphins, monkeys, cheetahs, frogs, newts, blindworms, salamanders, caecilians, and toads, are among the chordates most of us are familiar with.
Chordates are organisms that have a structure called the notochord at some point during their development into mature organisms. The Chordata phylum is divided into three subphyla: Cephalochordate, Vertebrata, and Urochordata. Chordates have a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail, among other features.
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