Difference Between Urochordata and Cephalochordata

Key Difference – Urochordata vs Cephalochordata
 

Urochordata and Cephalochordata are subphyla of Chordata. The key difference between Urochordata and Cephalochordata is based on their notochord extension. In Urochordata, the notochord is extended towards the posterior part, forming a tail in the larval stages. In Cephalochordata, the notochord is extended to the anterior part.

Phylum Chordata is composed of organisms having a notochord, a dorsal nerve cord and the pharyngeal slits. The Phylum Chordata is further divided into subphyla; Urochordata and Cephalochordata.

CONTENTS

1. Overview and Key Difference
2. What is Urochordata
3. What is Cephalochordata
4. Similarities Between Urochordata and Cephalochordata
5. Side by Side Comparison – Urochordata vs Cephalochordata in Tabular Form
6. Summary

What is Urochordata?

Urochordata is a sub phylum of the phylum Chordata. Urochordata are small sessile marine organisms in which the notochord is developed into a tail in the larval stages. The nerve cord present in the larval forms is dorsal and tubular. These organisms do not have a notochord or a nerve cord in the adult stages but possess a simple network of nerve ganglia.

The adult has a lump-like unsegmented body that is covered by a tunic. It has an inlet and an outlet for water flow. The interior of the Urochordates is a barrel-shaped structure. This is the main device in which food is stored. This barrel-shaped device also houses the internal gills that form the pharyngeal gill slits. Sea squirts and tunicates are organisms belonging to Urochordata.

What is Cephalochordata?

In Cephalochordata, the notochord develops into the anterior of the body structure, and the notochord is the main skeletal structure of the organism. The notochord remains throughout the lifetime and gives stability to the organism. The nerve cord is a dorsal nerve cord but is not fully developed to possess a true brain.

The organisms belonging to the subphylum Cephalochordata are marine and exist as solitary forms. They are usually buried in the sand. The digestive system is complete consisting of a tubular structure. The pharyngeal gill slits are highly developed and act as the feeding device in Cephalochordata. The body structures are developed as segmented bodies. Cephalochordates resemble the ancestral chordates. Amphioxus or lancelets are examples of Cephalochordates.

What are the Similarities Between Urochordata and Cephalochordata?

• Both Urochordata and Cephalochordata are marine organisms belonging to phylum Chordata.
• Both Urochordates and Cephalochordates subphyla possess a well-developed coelom.
• Both sub phyla possess pharyngeal gill slits.

What is the Difference Between Urochordata and Cephalochordata?

Summary – Urochordata vs Cephalochordata

Sub phyla Urochordata and Cephalochordata are two marine forms of chordates that have a varied development in relation to its notochord and nerve cord. The notochord and nerve cord in Urochordata are observed only during their larval stages, whereas in Cephalochordata they are observed throughout the adult lifespan. The presence of pharyngeal gill slits characteristic of chordates is observed in both subphyla.

Reference:

1.Satoh, Noriyuki, et al. “Chordate Evolution and the Three-Phylum System.” Proceedings of the Royal Society B: Biological Sciences, The Royal Society, 7 Nov. 2014. Available here  
2.Shaw, Michael, and University of Manitoba. “Animal Diversity I I Kingdom Animalia.” Biology 1030 – Biological Diversity, Function & Interactions. Available here  

Image Courtesy:

1.’Tunicate komodo’By Nhobgood Nick Hobgood – Own work, (CC BY-SA 3.0) via Commons Wikimedia  
2.’Branchiostoma lanceolatum’By © Hans Hillewaert (CC BY-SA 4.0) via Commons Wikimedia