Marine experts have made a fascinating discovery about the anatomy of starfish and other echinoderms. According to a study conducted by researchers at the University of Southampton, these creatures more closely resemble disembodied heads than multi-limbed creatures.
The study aimed to understand how echinoderms, which have a fivefold body plan, evolved from an ancestor with twofold symmetry. This body plan is common in animals such as insects, molluscs, and vertebrates. For a long time, scientists have been puzzled by the unclear relationship between different body parts of echinoderms and other organisms.
To unravel this mystery, the team focused on the adult body plan of starfish and analyzed which genes were active in the outermost layers of the animal. They compared these genes to the ones found in acorn worms and vertebrates, which have twofold symmetry. Interestingly, the majority of genes switched on in the outermost layers of the starfish body were similar to those activated in the heads of acorn worms and vertebrates.
Furthermore, the researchers discovered that different parts of the starfish arms correspond to different parts of the head. This finding suggests that starfish arms are more like extensions of the head rather than limbs as we would traditionally think of them. In essence, starfish can be described as a mostly head-like animal with five projections.
Dr. Jeff Thompson, a co-author of the study, explained that the study sheds light on how echinoderms ended up with their unique five-fold forms. The results also suggest that genes responsible for the trunk were lost from the outermost layers of echinoderms during evolution.
The implications of this research go beyond understanding starfish anatomy. Knowing how echinoderms evolved can provide valuable insights into interpreting early echinoderm fossils and comparing different brain regions between humans and echinoderms.
While the study focused on starfish, the researchers believe that the findings are likely applicable to other echinoderms as well. These findings represent a radical transformation of the ancestral bilaterian body plan and open avenues for further research into the evolution of marine life.
The study’s findings have been published in the journal Nature, accompanied by an opinion piece from Thurston Lacalli of the University of Victoria in British Columbia. Lacalli noted that the research not only enhances our understanding of echinoderms but also provides a foundation for interpreting early echinoderm fossils and comparisons between human and echinoderm brain regions.