Assertion: sea urchin's eye | /r/CapableOf | swivel in few cases
Facets:
value: to track prey
type: PURPOSE
Source sentences:
text: Their vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey.