Introduction:
Scientists investigating the mysterious body plan of starfish have made an astonishing discovery – the starfish head is essentially its entire body. This finding not only solves a longstanding puzzle but also offers insights into how animal forms evolve. Starfish, also known as sea stars, belong to a group of animals called echinoderms, which have unique body plans that differ from typical bilaterian animals like humans.
The Mystery of Echinoderms:
- Echinoderms, including starfish, lack a distinct head or tail end, instead having five lines of symmetry radiating from a central point.
- Despite these differences, echinoderms share a common ancestry with bilaterian animals.
- Scientists have struggled to compare equivalent body parts in echinoderms and bilaterians due to their profound differences in morphology.
The Study Approach:
- Researchers at Stanford University decided to study a set of genes known to govern the head-to-tail organization in bilaterian animals.
- These genes are expressed in specific patterns in the developing embryo, indicating which point on the head-to-tail axis it will become.
- The team aimed to uncover a “molecular anatomy” hidden in echinoderms by examining gene expression patterns.
The Surprising Findings:
- The genes that determine the head end in bilaterians were expressed in a line running down the middle of each arm on the underside of the starfish.
- Genes normally expressed in the trunk of bilaterians were absent in the outer layer of the starfish.
- This suggests that starfish have eliminated their trunk regions, allowing the outer layer to evolve in new directions.
Implications of the Discovery:
- The body of an echinoderm, particularly the outer body surface, can be seen as a walking head on the seafloor.
- This finding raises questions regarding the role of ecological factors in shaping the evolution of anatomy.
- Understanding underlying conserved patterns in development provides valuable insights into the evolution of different body plans.
By unraveling the mysteries of starfish anatomy, scientists are gaining a deeper understanding of the diversity and evolution of animal forms.
