In Evolutionary origins of sensation in metazoans: functional evidence for a new sensory organ in sponges, Danielle A Ludeman and her team at the University of Alberta document the heretofore unsuspected phenomenon of sneezing in freshwater sponges. When these sponges are stimulated with damaging sediment, they close their chimneys and inflate themselves to bursting, then abruptly "sneeze" out the irritants -- a process that unfolds very slowly (documented above in timelapse). I found out about this thanks to a fascinating interview (MP3) with the researcher on CBC Radio's As It Happens.
For their study, Ludeman and Leys used a variety of drugs to elicit sneezes in freshwater sponges and observed the process using fluorescent dye—all recorded using time-lapse video. Their efforts focused on the sponge’s osculum, which controls water exiting the organism, including water expelled during a sneeze.
Through a series of lab experiments, the pair discovered that ciliated cells lining the osculum play a role in triggering sneezes. In other animals, cilia function like antennae, helping cells respond to stimuli in a co-ordinated manner. In the sponge, their localized presence in the osculum and their sensory function suggest the osculum is in fact a sensory organ.
“For a sponge to have a sensory organ is totally new. This does not appear in a textbook; this doesn’t appear in someone’s concept of what sponges are permitted to have,” said Leys.
Sneezing sponges suggest existence of sensory organ [Bryan Alary/U Alberta] (via As It Happens)