For centuries, scientists have puzzled over whether sea stars, also known as starfish, have defined heads and tails due to their unique body plan. New genetic research has revealed that sea stars are largely heads without torsos or tails and likely lost those features over time through evolution.
Unique Body Plan
Sea stars, part of the echinoderm group that includes sea urchins, sand dollars, and sea cucumbers, have a unique body plan with five equal sections. This differs from the symmetric head-to-tail bodies of bilateral animals that have left and right sides mirroring each other.
From Bilateral to Pentaradial
Sea stars begin as fertilized eggs with a bilateral body plan but transform into a star shape, or pentaradial body, as they develop. This process has been a mystery for centuries.
Genetic Research Reveals Hidden Molecular Axis
Using micro computed tomography scanning and advanced analytical techniques, researchers identified genes that control the development of a sea star’s ectoderm, including its skin and nervous system. The study found genetic signatures associated with head development all over sea stars, concentrated in the center of the star and the center of each limb, while gene expression for torso and tail sections was largely absent.
Decoupling of Head and Trunk Regions
Sea stars “have the most dramatic example of decoupling of the head and the trunk regions that we are aware of today,” said lead study author Laurent Formery. The echinoderm body plan is roughly equivalent to the head in other animals.
Evolutionary Insights
The research suggests that sea stars and echinoderms evolved their unique body plans as their ancestors lost their trunk regions, allowing them to move and feed differently from other animals.
Complex Evolution
These findings have changed how scientists think about echinoderms and their evolution. Understanding these unusual creatures can shed light on the diverse ways different species remain healthy and help solve ecological and biomedical problems.
Broadening Biological Perspective
Exploring unusual animals and their unique ways of operating broadens the perspective of biology and contributes to solving complex scientific problems.