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taylorvich writes:

https://phys.org/news/2023-11-presumed-starfish.html

For centuries, naturalists have puzzled over what might constitute the head of a sea star, commonly called a "starfish." When looking at a worm, or a fish, it's clear which end is the head and which is the tail. But with their five identical arms—any of which can take the lead in propelling sea stars across the seabed—it's been anybody's guess how to determine the front end of the organism from the back. This unusual body plan has led many to conclude that sea stars perhaps don't have a head at all.

But now, labs at Stanford University and UC Berkeley, each led by Chan Zuckerberg Biohub San Francisco Investigators, have published a study finding that the truth is closer to the absolute reverse. In short, while the team detected gene signatures associated with head development just about everywhere in juvenile sea stars, expression of genes that code for an animal's torso and tail sections were largely missing.

Researchers used a variety of high-tech molecular and genomic techniques to understand where different genes were expressed during the development and growth of sea stars. A team at Southampton used micro-CT scanning to understand the shape and structure of the animal in unprecedented detail.

In another surprising finding, molecular signatures typically associated with the front-most portion of the head were localized to the middle of each of the sea star's arms, with these signatures becoming progressively more posterior moving out towards the arms' edges.

[...] "It's as if the sea star is completely missing a trunk, and is best described as just a head crawling along the seafloor," said Laurent Formery, a postdoctoral scholar and lead author of the new study. "It's not at all what scientists have assumed about these animals."

Journal Reference:
Formery, L., Peluso, P., Kohnle, I. et al. Molecular evidence of anteroposterior patterning in adult echinoderms. Nature (2023). https://doi.org/10.1038/s41586-023-06669-2

Original Submission