Turning performance in squid and cuttlefish: unique dual-mode, muscular hydrostatic systems

Area of Science:

• Marine Biology
• Biomechanics
• Animal Locomotion

Background:

• Unsteady swimming is crucial for aquatic animals but less studied than steady swimming.
• Cephalopods like squids and cuttlefish possess unique dual-mode propulsion (fins and jet) for locomotion.
• Quantitative analysis of cephalopod turning performance, a key aspect of maneuverability and agility, is lacking.

Purpose of the Study:

• To quantitatively assess the turning performance (maneuverability and agility) of brief squid (Lolliguncula brevis) and dwarf cuttlefish (Sepia bandensis).
• To investigate the biomechanical mechanisms underlying cephalopod turning, including the roles of jet propulsion, fin movements, and arm wrapping.
• To compare the turning capabilities of these cephalopods with other aquatic animals.

Main Methods:

• Filming brief squid and dwarf cuttlefish during turns using high-speed cameras.
• Tracking kinematic features to calculate the length-specific radius of the turn (R/L) for maneuverability and angular velocity (ω) for agility.
• Analyzing the relative contributions of jet flow, asymmetric fin motions, and arm wrapping to turning performance.

Main Results:

• Both L. brevis and S. bandensis demonstrated exceptional maneuverability, achieving the lowest reported R/L values for aquatic taxa.
• L. brevis exhibited higher agility (angular velocity) than S. bandensis.
• Jet flow was the primary driver of angular velocity in L. brevis; fin asymmetry and arm wrapping played secondary roles, varying by species.

Conclusions:

• Cephalopods possess high maneuverability and intermediate agility, reflecting their hybrid body architecture.
• Coordination between jet propulsion and fin movements is critical for effective turning.
• L. brevis excels in faster turns, while S. bandensis achieves tighter, more controlled turns, highlighting species-specific optimization of turning strategies.