Difference Between Radial and Spiral Cleavage

Key Difference – Radial vs Spiral Cleavage
 

Cleavage can be of two groups that highly depend on the amount of yolk in the egg. These two types are holoblastic (entire) cleavage or meroblastic (partial) cleavage. Radial and Spiral cleavage two types of holoblastic cleavage. Radial cleavage is present in deuterostomes while spiral cleavage is present in protostomes. This is the key difference between radial and spiral cleavage.

In the context of embryology, cleavage is defined as the division of cells during early embryo development. This is followed by the fertilization process, where this transfer is facilitated and triggered by the activation of cyclin-dependent kinase complex.

CONTENTS

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

What is Radial Cleavage?

Radial cleavage is defined as a type of cleavage that is present in deuterostomes, which is characterized by the arrangement of the blastomeres. They are arranged in a position that blastomeres of each upper tier are directly over those of the next lower tier. Deuterostomes that show radial cleavage include some vertebrates and echinoderms.

This arrangement results in radial symmetry that exists around the pole to pole axis of the embryo. In other terms, this arrangement could be described as an arrangement where the spindle axes are present parallel or present at right angles to the polar axis of the oocyte.

What is Spiral Cleavage?

Spiral cleavage is defined as a type of cleavage that is typically present in protostomes. Similar to radial cleavage in deuterostomes, spiral cleavage is also characterized by the presence of different special features. It is mainly the arrangement of the blastomeres of each upper tier over the cell junctions that are present in the lower tier, result in making the blastomeres arranged spirally around the pole to pole axis of the embryo.

Most of the animals that develop this type of spiral cleavage are referred to as spiralians that include taxa lophotrochozoa.  It is said that most of the spiralians undergo equal spiral cleavage whilst some of them undergo unequal spiral cleavage.

What are the Similarities Between Radial and Spiral Cleavage?

• Both Radial and Spiral Cleavage are holoblastic cleavages.
• Both occur in the embryonic stage.
• Blastomeres are involved in both Radial and Spiral Cleavage.
• Blastomeres are arranged in two tiers; upper tier and lower tier in both cleavages.

What is the Difference Between Radial and Spiral Cleavage?

Summary – Radial vs Spiral Cleavage

Cleavage is defined as the division of cells during early embryo development. Cleavage can be of two groups; holoblastic and meroblastic. Radial cleavage and spiral cleavage are two components of holoblastic cleavage. Radial cleavage is present in deuterostomes while spiral cleavage is present in protostomes. In radial cleavage, the developing embryo divided right angles to the previous division, resulting in four blastomeres situated directly above four others. In spiral cleavage, the division of cells in the developing embryo occurs in a spiral manner. This is the difference between radial and spiral cleavage.

Reference:

1.Valentine, James W. “Cleavage Patterns and the Topology of the Metazoan Tree of Life.” Proceedings of the National Academy of Sciences of the United States of America, The National Academy of Sciences of the USA, 22 July 1997. Available here
2.“Spiral Cleavage.” Merriam-Webster, Merriam-Webster. Available here  
3.“Radial Cleavage.” Merriam-Webster, Merriam-Webster. Available here 

Image Courtesy:

1.’Protovsdeuterostomes’By WYassineMrabetTalk – Own work, (CC BY-SA 3.0) via Commons Wikimedia 
2.’Spiral cleavage in Trochus’By Morgan Q. Goulding (CC BY 2.5) via Commons Wikimedia