Run and hide: visual performance in a brittle star

Area of Science:

• Marine Biology
• Sensory Ecology
• Echinodermata

Background:

• Spatial vision has been identified in the brittle star Ophiomastix wendtii, despite the absence of discrete eyes.
• The visual ecology and capabilities of this unique sensory system remain largely uncharacterized.

Purpose of the Study:

• To investigate the visual perception limits of Ophiomastix wendtii.
• To explore the potential defensive functions of vision in this species.
• To understand the role of vision in the behavior of Ophiomastix wendtii.

Main Methods:

• Behavioral experiments testing orientation to static vertical bar stimuli of varying angular widths and contrasts.
• Presentation of dynamic shadow stimuli (looming and passing) to assess defensive responses.
• Assessment of stimulus response in Ophiomastix wendtii with missing arms.

Main Results:

• Ophiomastix wendtii orients to large (≥50 degrees) and high-contrast vertical bars, suggesting a role in shelter-seeking.
• The study reports the first observed responses to moving stimuli in brittle stars, indicating potential defensive applications of vision.
• Photoreceptor sensitivity is low individually but likely enhanced by oversampling in arrays.
• Animals with a missing arm showed impaired orientation to static stimuli.

Conclusions:

• Ophiomastix wendtii utilizes spatial vision for navigation and predator avoidance.
• Vision in brittle stars may serve broader defensive roles than previously understood in echinoderms.
• Further research is needed to elucidate the functional significance of arm loss on visual orientation.