Naturalists have long struggled to make heads or tails of sea stars, aka starfish. While most animals have a head-to-tail body plan, the anatomy of sea stars, with their five radiating arms, defies usual classifications. Considering that they have no brain, you might conclude they have no head at all.
Au contraire. Far from headless, starfish are mostly head, according to a study from Stanford and UC Berkeley that used genetic and molecular tools to create a 3D atlas of gene expression throughout sea stars’ bodies. The researchers found genetic signatures associated with head development in other animals distributed throughout the sea star’s arms and center, while discovering a small amount of genetic patterning for a tail and none for a trunk.
“It’s as if the sea star is completely missing a trunk and is best described as just a head crawling along the seafloor,” lead author Laurent Formery, a postdoc in the lab of Stanford biology professor Christopher Lowe, said in a news release. The fossil record shows sea stars’ ancestors appeared to have torsos, which raises a new question: When in evolutionary time did sea stars lose their swim trunks?
Sam Scott is a senior writer at Stanford. Email him at sscott3@stanford.edu.
