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As planktonic organisms the larvae of the marine annelid Platynereis swim freely in the open water. They move by activity of their cilia, thousands of tiny hair-like structures forming a band along the larval body and beating coordinately. With changing environmental conditions the larvae swim upward and downward to their appropriate water depth. Scientists of the Max Planck Institute for Developmental Biology in Tbingen, Germany have now identified some signalling substances in the larval nervous system regulating swimming depth of the larvae. These substances influence the ciliary beating and thus hold the larvae in the preferred water depth. The scientists discovered a very simple circuitry of nerve cells underlying this regulation, reflecting an early evolutionary state of the nervous system.
The locomotory system of many animals is muscle based. However, small marine animals often move by cilia. This type of locomotion is more ancient in evolution than muscle-based locomotion and very common in marine plankton. Besides the annelid larvae, the larvae of many marine invertebrates are part of this plankton, for example larvae of snails, sea shells and starfish.
"Not much is known about how the nervous systems of the marine plankton regulate ciliary beating, since the locomotion of intensely explored model organisms like the fruit fly is based on muscles," says Gspr Jkely. Together with his team at the Max Planck Institute for Developmental Biology and in cooperation with Thomas A. Mnch at the Centre for Integrative Neuroscience in Tbingen, he has examined in detail the nervous system of marine annelid larvae of Platynereis dumerilii.
The ciliary band of Platynereis larvae serves as a swimming motor in the seawater: When cilia beat fast and continuously, larvae swim upward
|Contact: Gaspar Jekely|