Extraocular vision in the sea urchin Diadema setosum

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10 Citations (Scopus)


In most organisms, specific structures are responsible for detecting light patterns and vision. Several species of sea urchins appear to have a diffuse photoreceptor system that enables them to detect light and in some cases objects. The presence of extraocular vision was investigated on a sea urchin common in northern Oman, Diadema setosum. Urchins from 8- to 10-m deep coral communities were used in controlled experiments that quantified the orientation response of the urchins to various visual cues: size, contrast and colour of circular targets simulating urchins’ outlines. Urchins responded to black discs down to 11° initial visual angle but not to smaller discs. The minimum grey-scale value triggering a response was between 50 and 37% black. Urchins responded to red targets but not to green or blue ones. An average angular distance between spines of 5.3° suggested a visual acuity of about 10.6°. D. setosum thus showed extraocular vision allowing them to detect objects of different sizes, contrasts and to some extent colour, supporting the hypothesis that the whole sea urchin’s body acts as a single large compound eye.
Original languageEnglish
Pages (from-to)31-40
Number of pages10
JournalMarine and Freshwater Behaviour and Physiology
Issue number1
Publication statusPublished - Jan 2 2017


  • Diadema setosum
  • Echinoidea
  • Extraocular vision
  • behaviour
  • sea urchin

ASJC Scopus subject areas

  • Oceanography
  • Physiology
  • Aquatic Science


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