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If you’ve had hayfever this summer, or even suffered from the common cold, spare a thought for sea sponges. Far from being able to grab a hanky, these creatures are among the oldest extant multicellular organisms on Earth, and guess what? They sneeze too. 

Before now, it was commonly assumed that sponges transported waste products out of their bodies along with the water flow, through their central outflow opening called an osculum. However, the removal of sediments has even been seen from the seawater inlet pores (ostia) rather than the osculum.  

While marine experts have known about this behavior for a long time, new research published in the journal Current Biology has revealed a new waste disposal system. These sponges move mucus, containing waste particles, against their internal flow of water out of their ostia and into the surrounding water column by a period of surface contractions – or “sneezing”. 

Researchers recorded a time-lapse video of the stove-pipe sponge (Aplysina archeri). In the video, the sponge can be seen expelling particulate matter through its inlet pores. 

The video also shows that mucus is continually moving across the surface of the sea sponge, creating “mucus highways” that contain waste material. These highways became junctions at specific elevated sections on the sponges' surface with the mucus forming stringy clumps. These stringy clumps of mucus, basically the equivalent of sea sponge snot, were then expelled into the water column by a series of contractions and relaxations across the sponges’ surface. 

“Let’s be clear: sponges don’t sneeze like humans do. A sponge sneeze takes about half an hour to complete. But both sponge and human sneezes exist as a waste disposal mechanism,” said Jasper de Goeij, a marine biologist at the University of Amsterdam and the senior author of the study, in a statement.

The sea sponge snot has benefits beyond unclogging the internal pores of A. archeri. The researchers also found that other animals that live alongside the sponges feed on the mucus that the sponges produce. Apparently picking your nose and eating it is allowed in the sea sponge world as long as the eating is done by someone else. Thia may be an unexpected benefit when wearing a sea sponge as a hat.

“Some organic matter exists in the water surrounding the coral reef, but most of it is not concentrated enough for other animals to eat. Sponges transform this material into eatable mucus,” said Niklas Kornder, the first author of the study in a statement.

While the paper recorded two species of sponges exhibiting this sneezing behavior, Kornder thinks that almost all sponges sneeze. “We actually think that most, if not all, sponges sneeze. I’ve seen mucus accumulate on different sponges while diving and in pictures taken by other scientists for other purposes”.  

The next step for the researchers is to investigate more into the mucus highways and understand why the sponge snot is traveling in what appears to be defined paths. 

Eleanor is a content creator and social media assistant with an undergraduate degree in zoology and a master’s degree in wildlife documentary production.

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