Judy Taylor
[lwptoc]
Introduction: Horses and Chordata phylum
The horse, scientifically known as Equus ferus caballus, is a domesticated mammal that belongs to the Chordata phylum. Chordates are animals that possess a notochord, dorsal nerve cord, pharyngeal gill slits, endostyle or thyroid gland, post-anal tail, bilateral symmetry, segmented muscles, and deuterostome development at some point in their life cycle. These characteristics set chordates apart from other animals and justify the inclusion of horses in this phylum.
Presence of notochord in horses
One of the defining characteristics of chordates is the notochord, a long and flexible rod that runs beneath the nerve cord. In horses, the notochord is present during embryonic development and is eventually replaced by the vertebrae. The notochord provides support and allows for movement in chordates, making it essential for the development of the musculoskeletal system in horses.
Dorsal nerve cord in horses
Another feature of chordates is the dorsal nerve cord, which is situated above the notochord and runs along the length of the body. In horses, the dorsal nerve cord is protected by the vertebrae and plays a crucial role in transmitting neural signals throughout the body. This structure is responsible for the coordination of movement, sensation, and cognition in horses, making it a vital component of their nervous system.
Pharyngeal gill slits in horses
Pharyngeal gill slits are another characteristic that justify the placement of horses under the Chordata phylum. These structures are present in the developing embryo and are used for respiration and feeding in aquatic chordates. Although horses are not aquatic animals, they still possess pharyngeal gill slits during embryonic development, which eventually become the eustachian tubes and the middle ear cavity.
Endostyle or thyroid gland in horses
The endostyle or thyroid gland is a structure located in the pharynx of chordates and is responsible for the production of iodine-containing hormones that regulate metabolism. In horses, the endostyle develops into the thyroid gland, which plays a crucial role in maintaining metabolic homeostasis. The thyroid gland produces hormones that regulate the rate of metabolism, growth, and development in horses, making it a vital structure in their physiology.
Post-anal tail in horses
The presence of a post-anal tail is another feature that sets chordates apart from other animals. The post-anal tail is a muscular structure that extends beyond the anus and is used for balance, movement, and communication in some chordates. Although horses do not possess a tail in the traditional sense, they do have a vestigial structure called the coccygeal vertebrae that is considered a remnant of the post-anal tail in their evolutionary history.
Bilateral symmetry in horses
Bilateral symmetry is a characteristic that refers to the arrangement of body structures in a mirror image along a central axis. Chordates, including horses, exhibit bilateral symmetry, which allows for the development of specialized structures for feeding, sensing, and locomotion. The presence of bilateral symmetry in horses is evident in their paired limbs, sensory organs, and other structures that are arranged in a symmetrical pattern along the body.
Segmented muscles in horses
Chordates also possess segmented muscles, which are muscles that are arranged in repeating units along the length of the body. In horses, segmented muscles are evident in the arrangement of the myotomes, which are the individual units that make up the skeletal muscles. This arrangement allows for precise and coordinated movements, making it an essential feature of the musculoskeletal system in horses.
Deuterostome development in horses
Finally, chordates undergo deuterostome development, which is a type of embryonic development characterized by the formation of the anus before the mouth. This type of development is unique to chordates and sets them apart from other animals. In horses, deuterostome development is evident in the formation of the anus before the mouth during embryonic development.
Conclusion: Horses as Chordates
In conclusion, horses possess all the defining characteristics of chordates, including the presence of a notochord, dorsal nerve cord, pharyngeal gill slits, endostyle or thyroid gland, post-anal tail, bilateral symmetry, segmented muscles, and deuterostome development. These features justify the placement of horses under the Chordata phylum, making them part of a diverse group of animals that share a common ancestry and evolutionary history.
