What looks like bright orange modern art is actually spherical larvae of the marine annelid Platynereis under the microscope. The hair-like projections on the outside are called cilia. They beat like tiny oars so that the larva can feed, move, avoid predators and reach the appropriate habitat. The correct coordination of the cilia is essential for this.
However, despite decades of research, until recently it was unclear how the coordination of cilia movement works. In particular, the formation of effective, metachronal waves – patterns that move like a La-Ola wave through the densely packed rows of cilia – has been a mystery until now. To shed light on the matter, a team from the University of Exeter has now examined Platynereis larvae and used high-speed images to analyze the wave movements of their cilia.
The result: Although at first glance it appears as if the La-Ola wave is spreading across cell boundaries, the cilia actually only coordinate their movements within individual cells. The waves themselves are created by short-range “steric” interactions: cilia collide with each other and thus keep their movements synchronized. This means the larvae can still swim even if individual cilia are damaged.
“Marine plankton form the basis of food webs. Cilia are crucial for their effective distribution and their ability to control their position within the water column – without them, the marine ecosystem would collapse,” emphasizes senior author Kirsty Wan. It is all the more important to better understand the way of life of the tiny sea creatures and the function of their “rudders”.