Animal Taxonomy Part 1: Phylum Chordata Characteristics

Study Notes

Phylum Chordata

Phylum Chordata is the most notable phylum, including all human beings, animals, and birds.
The distinguishing character of all animals in this phylum is the presence of notochord.
Chordates show four features at different stages in their life:
Notochord
Dorsal Nerve Cord
Post-anal tail
Pharyngeal slits

Dorsal Nerve Cord

A bundle of nerve fibers that connects the brain, muscles, and other organs.
Formation of Nerve Cord: a dorsal, hollow, longitudinal rod made of cartilage, running between the nerve cord and the digestive tract.
Its main function is to support the nerve cord.

Pharyngeal Slits

Openings that connect the mouth and the throat.
Allow the entry of water through the mouth, without entering the digestive system.

Subphylum Craniata

Occupy almost every environment: surface of the earth, marine and freshwater habitats, and terrestrial habitats.
Primitive members are agnathans (without jaws), lacking rigid hinged elements supporting the borders of the mouth.
Most members have the vertebral column that replaces the notochord and are called vertebrates.
They possess jaws and are known as Gnathostomata.

Common Features of Craniate

Bilateral symmetry: the arrangement of the organ systems in the right and left halves of the animal is exactly similar.
Cephalization: the anterior end of the animal is differentiated into a distinct head region.

Body Organization

Body is divisible into three regions: head, trunk, and tail.
Possess a well-developed head region and cranium.
Notochord is replaced by vertebral column either partly or wholly in the adult.
Nerve cord is differentiated into brain and spinal cord in the adult.

Organ Systems

Possess well-developed organ systems showing a higher grade of organization and functional efficiency.
Circulatory system: blood is confined to arteries, veins, and sinusoids with a well-developed muscular heart with two, three, or four chambers.
Respiratory system: in the lower forms, by paired gills, and in terrestrial species, by lungs.
Excretory system: the paired excretory organs (kidneys) discharge through ducts or ureters near or through the anus.
Nervous system: the brain becomes regionally differentiated as to structure and function.

Reproductive System

The sexes are separate, and each has a pair of gonads.
Development of the embryos may take place in different ways, and they can be: Oviparous, Ovoviviparous, and Viviparous.

Endocrine Glands

Provide hormones, transported by the bloodstream, that regulate bodily processes, growth, and reproduction.

Division (i): Agnatha

Marine or freshwater forms, distinct from other Vertebrates in the absence of jaws and paired fins or appendages.

Division (ii): Gnathostomata

Higher vertebrates possessing true jaws.
In most vertebrates, the embryonic notochord is replaced by a vertebral column.
They are further divided into two superclasses: Pisces and Tetrapoda.

Superclass: Pisces

Includes cartilaginous and bony fishes.
Mouth terminal or subterminal with different types of feeding habitats.
Four pairs of gills present, covered by a flexible plate called an operculum.
Gills are filamentary type, and an air bladder or swim bladder is often present.

Superclass: Tetrapoda

Means "four legs".
All tetrapods have a basic pentadactyl (five-digit) limb structure.
Amphibians, reptiles, birds, and mammals are the major groups of the Tetrapoda.
Tetrapods include all land-living vertebrates and also include a number of animals that live in the water, such as sea turtles, sea snakes, whales, and dolphins.

Class: Amphibia

Amphibians are the first tetrapods showing many transitional modifications from aquatic to terrestrial life.
The name Amphibia refers to a double life, leading a life both on land and in water.
They are partially terrestrial, as they have to return to water for breeding and development.
Cold-blooded vertebrates, viviparous vertebrates which give birth to young ones, except monotremes which are egg-laying mammals.

Description

Learn about the key characteristics of animals in the phylum Chordata, including the presence of a notochord and a dorsal nerve cord. Explore the unique features that define chordates at different life stages.