Table of Contents
- Classification of Cephalochordata
- General Characteristics of Cephalochordata
- Frequently Asked Questions
Cephalochordata is a subphylum in the phylum chordata. The animals belonging to this subphylum are known as cephalochordates, lancelets or amphioxus. They are marine animals that possess a segmented and elongated body. They also contain a notochord that extends from the head to the tail.
All in all, they possess many typical chordate features but lack true vertebrate features, hence their separate division. The cephalochordates have been believed to diverge from the chordate subphylum around 700 million years ago. Read this article to learn more about cephalochordates.
Classification of Cephalochordata
General Characteristics of Cephalochordata
- The subphylum cephalochordata is found inhabiting shallow temperate and tropical oceans, buried in coarse sand.
- Cephalochordates possess five characteristics that are found in all chordates at some point in their life. They are:
- A notochord
- Dorsal hollow nerve cord
- Pharyngeal slits
- Post-anal tail
- The subphylum cephalochordata possesses around thirty species in two families, making it the smallest phyla in the animal kingdom.
- Branchiostoma of the family Branchiostomatidae is the most common genus of the subphylum.
- They are also known as acraniates because they do not possess a true brain, braincase or cranium as found in vertebrates.
- The pharynx has many gill slits that are surrounded by an atrium for protection.
- The body of lancelets, like other vertebrates, is made up of segments that are known as metameres.
- The segmentation helps in the more effective locomotion of the organisms.
- A secondary body cavity, similar to coelom in vertebrates, is also found in cephalochordates.
- Externally, they have a dorsal fin that extends from the upper surface of the body and continues into a caudal fin around the tail and finishes as a ventral fin to the lower surface of the atrium.
- There are no paired fins found.
- The notochord extends through the entire body and provides the required support to the organisms.
- The nervous system is composed of the hollow nerve cord that possesses a small swelling which is barely qualified as the brain.
- Small eyelike organs are found in the nerve cord that detect light, its direction and change in intensity.
- For digestion, their mouth is covered with an oral hood that is the entrance for incoming food particles.
- The edges of the oral hood have Buccal cirri that are filament-like projections. They filter out any large food particles from entering the buccal cavity.
- Respiration takes place with the help of gills that possess gill slits.
- The circulatory system of cephalochordates is closed and is very similar to vertebrates. The only striking difference is that they lack a heart.
Visit BYJU’S Biology for more information.
You might also be interested in:
- Phylum Chordata – Characteristics, Classification and Examples
- Protochordate – Characteristics, Classifications and Examples
- Difference between Lancelets and Tunicates