Buzz
Experts have long established an evolutionary timeline detailing when and how animals first evolved anal openings. However, as Amy Maxmen notes in Science, this timeline was recently challenged by footage of comb jellies defecating. The scientist responsible for the video showcased his discoveries at Ctenopalooza (a comb jelly research symposium) in St. Augustine, Florida, earlier this month.
Sea walnuts are part of a group of jellyfish-like creatures known as comb jellies or ctenophores, which lack tentacles. Their unique appearance sets them apart: they resemble translucent, gelatinous orbs adorned with shimmering, rainbow-like lights, as if a glowing Las Vegas were encased in a massive, wobbly dome.
Similar to many ocean-dwelling invertebrates, comb jellies possess a remarkably basic anatomy: a soft, tubular structure with one opening serving both as a mouth and an anus. At least, that was the prevailing belief—until William Browne’s video emerged, challenging this assumption.
The evolutionary biologist from the University of Miami has been cultivating sea walnuts (Mnemiopsis leidyi) and their relatives, sea gooseberries (Pleurobrachia bachei), in his laboratory. During his experiments, he recorded them expelling waste through their anal openings. By using small crustaceans and zebrafish genetically modified to emit a red fluorescent glow, he successfully tracked the entire digestive process from consumption to excretion.
Though it might seem insignificant or even amusing to some, the identification of anal openings in comb jellies is a groundbreaking revelation for scientists. The evolution of anuses marks a significant divergence in animal development. For eons, creatures functioned without them. Once they evolved, every subsequent species inherited them. Ctenophores, existing for over 550 million years, were presumed to belong to the pre-anus era. However, this discovery challenges that assumption.
When Browne presented the enlightening footage, the audience of specialists was left in awe. “It appears I’ve been mistaken for three decades,” marine biologist George Matsumoto remarked to Science. “Without seeing this video, people simply won’t accept it.”
This isn’t the first instance where sea walnuts have disrupted evolutionary theories. In 2014, geneticists discovered that these jellies appear to have carved out a unique evolutionary trajectory in the development of their nervous systems.
