Different Synchrony in Rhythmic Movement Caused by Morphological Difference between Five- and Six-armed Brittle Stars

Area of Science:

• Marine Biology
• Biophysics
• Robotics

Background:

• Neuronal activity is known to coordinate rhythmic movements in animals.
• Robotics research highlights the role of body structure (morphology) in movement.
• The independent effect of morphology on animal movement coordination remains unclear.

Purpose of the Study:

• To investigate how morphology affects movement coordination independent of neuronal activity.
• To explore rhythmic movement patterns in the green brittle star Ophiarachna incrassata.
• To model the role of internal fluid dynamics in coordinating movement.

Main Methods:

• Observation of rhythmic movement in Ophiarachna incrassata.
• Development of a phenomenological model simulating internal fluid flows.
• Simulation of altered morphology (changing body parts) to predict movement patterns.

Main Results:

• Ophiarachna incrassata exhibits unsynchronized rhythmic movement of its five radially symmetric body parts.
• The phenomenological model successfully explained this pattern through internal fluid dynamics.
• Simulations showed that changing to six body parts resulted in synchronized movement, confirmed in a six-part individual.

Conclusions:

• Morphology, specifically the number of body parts, influences fluid flow dynamics.
• Altered fluid flow patterns lead to different synchronization patterns in rhythmic movements.
• This study provides a model for understanding morphology-driven movement coordination without neuronal input.