Phylum-Chordata

Introduction

In biology, a phylum is the third level of categorisation, after domain and kingdom. A phylum’s organisms are distinct from other phyla because they have a shared set of features. Chordata is a broad class of species that comprises not just vertebrates but also lancelets and sea squirts, among other things.

The phylum Chordata includes various vertebrates such as amphibians, mammals, fish, and reptiles. Chordata is a phylum of animals that includes both invertebrate and vertebrate chordates. Phylum is a big and varied group of organisms. It has around 60,000 different species.

Chordata 

 Animals of the phylum Chordata are known as chordates. It is possible to describe chordates as having four anatomical characteristics, namely, notochord, dorsal nerve cord, a post-anal tail, and pharyngeal slits. One of the characteristics of Chordata, as the name indicates, is that it has a strong, dorsal supporting rod at some point throughout its life cycle (the notochord).

Anus and anus-like structures like the hollow nerve cord that extends above and below the anus are also seen in chordates. In addition, chordates have an endostyle (or its descendant) or endoscopy (a mucus-secreting structure) in between gills, as well as a tail that runs behind the anus.

Chordata features

A notochord, pharyngeal slits, a post-anal tail, and a dorsal hollow nerve cord are all traits shared by animals in this phylum.

Notochord

What gives Chordata its name is the notochord, a rigid yet supple rod of cells and interconnecting tissue (from the Greek roots ‘noto’ denoting back and ‘chord’ denoting string). Some chordates rely heavily on the notochord for structural stability. No adult form of a vertebrate or bird has a notochord; only the developing embryo does.

Since they develop bony, clustered vertebrae in their later stages, these organisms are categorized as Vertebrata. Because they have a notochord that does not develop a vertebral column, they are classified as invertebrate chordates.

Pharyngeal slits

As the name suggests, the pharyngeal slit is located below the mouth (or oral cavity) and spreads into the surroundings. Invertebrate chordates utilize these apertures for internal fertilization. The pharyngeal slits allow water to enter the mouth, filtering food particles as it departs.

The pharyngeal slits of aquatic animals like fish ultimately become gills or jaw supports (as in jawed fishes). The pharyngeal slits like those seen in mammals and birds are visible at the embryonic stage and later become part of the ears and tonsils.

Dorsal hollow nerve tube

Above the notochord, the dorsal hollow neural tube transmits nerve tissue to muscles and other parts. The nerve tube’s walls get thicker as it develops, reducing the empty middle area to a minimum. In the embryonic and adult stages, every Chordata, including humans, have a dorsal hollow nerve tube.

Post-anal tail

The post-anal tail is a term used to describe the posterior extension of the body, which continues beyond the anus. Skeletal elements and muscles may be found in the post-anal tail of aquatic chordates. The post-anal tail is critical to the organism’s ability to move about in its aquatic environment.

General Characteristics of the Phylum Chordata 

• A proportion of cephalisation may be found
• The phylum Chordata is symmetrical on both sides
• Chordates are the richest diversified phylum in the animal world, even though they are not the largest
• They have a complete circulatory system (blood remains contained inside vessels at all times)

Life Cycle and Reproduction

The phylum Chordata includes all vertebrates that have a vertebral column, tunicates, and lancelets. When it comes to sexual reproduction, two techniques are employed: internal and external fertilization. It is thought that sperm and eggs join together inside the body during internal fertilization to produce a child. Because sperm fertilizes the egg outside the body when external fertilization is used, aquatic creatures are the only ones capable of this kind of implantation.

Instead of a spine, several species of lancelets in the subphylum Cephalochordata have a nerve cord supported by the notochord, like a small fish. During the mating season, males and females generate sperm and eggs that may be fertilized simultaneously. The gonads eventually burst during spawning, flushing the gametes into the water. Reproduction may be sexual or asexual in the subphyla Urochordata and Vertebrata.

Male and female fish release gametes in large quantities for external fertilization, ensuring a successful reproductive process in fish. Amphibians also use external fertilization to reproduce. 

Classification of Phylum Chordata

Urochordata, Cephalochordata, and Vertebrata are the three subphyla. In comparison to complicated vertebrates, the first two are primitive.

There are additional classifications and traits to examine invertebrates. The initial two subphyla are protochordate and are marine. The notochord is exclusively found in the embryonic tail of the Urochordata. Cephalochordata, on the other hand, possesses a notochord across its body. The classification of Chordata includes Ascidia, Doliolum, Salpa, and Amphioxus.

A notochord, triploblastic, dorsal nerve cord, and coelomate are all frequent components in chordates. Vertebrates are the phylum Chordata’s last categorization. They are further divided into subclasses based on factors such as circulation and metabolism.

Conclusion

Chordates are organisms that typically contain a feature known as the notochord for a portion of their evolution into mature organisms. Cephalochordate, Vertebrata, and Urochordata are the three subphyla of Chordata.