Viscous Sea Hare

At shallow depth, on a bottom covered with algae, a large sea hare progresses slowly in front of the diver. Its two rhinophores raised evoke the ears of a hare, but this detail still reveals nothing of what makes Aplysia depilans remarkable.

The surprise can begin when a second individual appears, then a third: the species is hermaphroditic and its mating often occurs in chains of several animals. A chain of six individuals with a spawning event has even been documented in this species.

Yet its most unexpected story remains invisible underwater. Its abdominal ganglion contains nerve cells that are exceptionally large, some reaching several hundred micrometers.

This particularity made it a valuable animal for the first work in cellular neurophysiology: from the 1960s onwards, researchers could introduce microelectrodes into identifiable neurons and study their functioning directly. Eric Kandel and Ladislav Tauc thus published in 1965 experiments conducted on the neurons of the abdominal ganglion of Aplysia depilans, including its giant cell.

Then the animal simply continues its way among the algae, its 'ears' in the current, without its silhouette revealing the experiments once conducted at the heart of its nervous system.