Phylum Chordata: Definition, Characteristics, Examples, Classification, Facts, Reproduction

Introduction to Phylum Chordata

Phylum Chordata is a significant grouping in the field of biology because the animals belonging to this phylum have a notochord at some point in the development process. Subphyla in this include

• Urochordata (also called Tunicates)

• Cephalochordata (also known as Lancelets)

• Vertebrata (which includes all vertebrates like fish, amphibians, reptiles, birds, and mammals)

Formation of the notochord, open dorsal nerve cord, and pharyngeal slits can be considered as a hallmark of chordates. These chordates are very important in the study of the evolution of animals because they show a rich variation extending from the simplest filter-feeding organisms like tunicates to the highest-developed forms like mammals, birds, and reptiles. It is, therefore, apparent that this evolutionary history outlines the factors that have made chordates live in different environments, as well as demonstrating their roles in the study of biology and evolution.

General Characteristics of Chordata

The phylum Chordata is defined by a set of unique features that appear at some stage in the life cycle of all chordate animals. These features include the notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. The characteristics are described below.

• Notochord

The notochord is a muscular, fluid-filled rod, which is the precursor of the vertebral column and the embryonic organiser. It does in cephalochordates throughout life, but in vertebrates, it is replaced by a vertebral column to have a more supportive and protective structure.

• Dorsal Hollow Nerve Cord

This long, threadlike bundle of nerve cells transmits impulses, and in vertebrates, it makes up the brain and the spinal cord. Dorsal nerve cords of chordates are compared to ventral nerve cords of arthropods and annelids, and the basic and functional differences are discussed.

• Pharyngeal Slits

A branchial cleft in the embryonic pharynx, which was concerned with filter feeding and then became modified for respiratory purposes in fish and among the higher vertebrates, becomes the auditory and pharyngeal opening. These slits change their roles to serve as the respiratory apparatus in fish and the development of structures in terrestrial vertebrates.

• Post-Anal Tail

The post-anal tail is involved in movement and stability and used in propulsion within a water environment. Although useful in the locomotion of many chordates, the tail is partially developed or absent in some forms, such as humans, in various amounts depending on the evolutionary pressures on a certain species.

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Phylum Chordata Classification

The Phylum Chordata is divided into three major subphyla: Urochordata, Cephalochordata, and Vertebrata. The classification of chordata helps in organizing a wide variety of animals, from simple tunicates to complex mammals. The classification is described as

1. Subphylum Urochordata (Tunicates)

Subphylum Urochordata includes Tunicates, which have a bag-like body and are protected by a skin called a tunic. They have a notochord and nerve cord only at a larval stage. Members of this group are important in their biome as filter feeders and also as a food source for other marine organisms.

2. Subphylum Cephalochordata (Lancelets)

Subphylum Cephalochordata includes Lancelets, which are characterised by their elongated, fish-like body structure and also contain a notochord throughout their body and a very simple nervous system. It is found buried in sandy substrates with its head pointed up, and it filters on microorganisms. Lancelets are known to feed on various matters found in the sea and to constitute a significant part of the marine trophic pyramid. Besides, they are believed to be ideal for the study of vertebrate evolution owing to their plesiomorphic features.

3. Subphylum Vertebrata

Class Agnatha (Jawless Fishes)

Lampreys and hagfish, as well as other related species, do not have jaws and paired appendages. They possess cartilaginous skeletons and pucker-like mouths and do not possess paired limbs or limbs in general. Lampreys are found both in sea and freshwater habitats, mostly as parasites, while hagfish are found in the deep sea and feed on dead and dying fish.

Class Chondrichthyes (Cartilaginous Fishes)

Class Chondrichthyes includes cartilaginous fishes like sharks, rays, and skates. These fish have skeletons made of cartilage (not bone), making them lightweight and flexible. They have paired fins, a powerful tail, and leathery skin covered with tiny placoid scales (tooth-like structures). They exhibit good sense organs and features that would contribute to efficient hunting for an organism. Sharks and rays are important predators in the marine food chain, which regulates the populations of the species in the marine biomes.

Class Osteichthyes (Bony Fishes)

Class Osteichthyes can be of different forms and sizes depending on the number of bones found in them and are characterised by a skeletal system of bone. They are found in different ecosystems, from freshwater to deep-sea environments forms. As the world’s major protein source, they constitute a critical link in food chains and have distinct importance for human diets and the economy.

Class Amphibia

Amphibians, including frogs, salamanders, and newts, begin their lives in water but live on land as adults. They have features such as slimy skin to do cutaneous breathing and limbs for moving on land. Actually, amphibians are very sensitive to any changes and the presence of pollutants in the environment and thus can serve as very good bioindicators. Conservation measures are essential because their populations decline due to habitat destruction, the alteration of climate, and diseases, such as chytridiomycosis.

Class Reptilia

Terrestrial adaptations found in reptiles include having armored skin that is keratinized to reduce the rate at which water is lost, efficient lungs for breathing air, and laying eggs on land through amniotic eggs. Reptiles include snakes, lizards, turtles, alligators, and crocodiles. It can be used as pest control, food for other animals, and boost the delicacy of an ecosystem by hunting for food and taking part in the scavenging process.

Class Aves (Birds)

The species of aves have light bones, structures called feathers and highly developed flight muscles. This makes them reside in different ecosystems ranging from forests and wetlands to cities and towns and even the ocean. Different species of birds are endangered due to many factors such as loss of habitat, climate change, and pollution. Nevertheless, they are threatened for many reasons, and still, they host over one hundred and ten thousand individual species differentiated within various ecological positions.

Class Mammalia

Mammals are outlined by the possession of mammary supplements, which produce milk, body hair or fur, and thermoregulation. These features allow them to survive in many habitats. All mammals have many specific branches resulting from limb modifications like special teeth and a developed brain, which helps them to live in hot deserts or polar regions or forests. Thus, flexibility has brought out the ability of mammals to inhabit all the habitats on this planet.

Phylum Chordata Examples

The classification of Phylum Chordata with examples is commonly asked in exams. Here are the major classes of chordates with examples from each group:

• Urochordata: Herdmania

• Cephalochordata: Branchiostoma (Amphioxus)

• Agnatha: Petromyzon (Lamprey)

• Chondrichthyes: Scoliodon (Dogfish)

• Osteichthyes: Labeo (Rohu)

• Amphibia (Amphibians): Frog, Salamander, Toad

• Reptilia (Reptiles): Snake, Lizard, Crocodile

• Aves (Birds): Eagle, Sparrow, Penguin

• Mammalia (Mammals): Human, Elephant, Dolphin

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