Meeting Abstract
Starfishes possess compound eyes at the tip of each of their arms. Some species use low-resolution vision to navigate towards the reef. But the mechanisms of visual coding remain largely unknown. Here we describe the morphology and show the adaptation pattern of the eye. The eyes sit on the terminal tube foot and have dozens of orange ommatidia. SEM images show the diameters of the surface of ommatidia vary from 10μm to 40μm. Those closer to the ambulacral groove are considerably larger than the rest with a diameter around 35μm and more folding and evaginating subunits within. The eyes are surrounded by a crown-like structure made up of 20 to 30 hardened tube feet. Purple modified tube feet were located oral and proximal to the eye. When exposed to pulses of light for 80ms or more, we recorded a maximum field potential of ~100-350 μV with a suction electrode in contact with 1-4 ommatidia. The crest-to-trough duration ranged from 1.5s-1.7s regardless of stimulus intensity. As the duration of light stimuli decreased, the response amplitude showed a negative concave down curve. Repetitive light stimuli showed frequency-dependent adaptation. Light pulses with 67s intervals (0.015 pps) elicit responses with decreasing amplitude. After 5 stimuli, the response decreased to 85% of the initial response. When exposed to light pulses with 20s intervals (0.05 pps), however, the pattern is different. The second response dropped to 42% of initial response and the third response recovered to 50%. From there, the responses decreased with repetitive stimuli. At the 7th stimulus, the responses returned to the same amplitude of the second response. With high-frequency stimuli at 10s intervals, the adaptation was strong with the second and subsequent responses dropped to 20% of the initial response. There seemed to be a fast, large response merged with a slow, small response.
