Convergence; in vision (Introduction)

by David Turell , Saturday, November 21, 2015, 05:59 (3083 days ago) @ David Turell

Another version of vision is seen in Acanthopleura granulate, a mollusk, also using crystal lenses as seen in Trilobites:-http://www.livescience.com/52857-mollusk-has-eyes-made-of-armor.html?cmpid=NL_LS_weekly_2015-11-20-Acanthopleura granulata is a chiton, a pill bug of the sea. This animal has a shell made of overlapping plates, which allows it to roll up in defense if a predator manages to pry it from the tidal-zone rock it calls home. Researchers have long known that chitons have soft tissue embedded in their flexible suits of armor, and that some of this soft tissue is sensitive to light. Now, they've discovered that A. granulata has hundreds of actual eyes that can see an 8-inch-long (20 centimeters) fish from 6.5 feet (2 meters) away.-Even weirder, these eyes are made of the same calcium-carbonate mineral as the chiton shell. However, the animal does have to trade off some structural integrity in return for the sensory function.-***-The researchers examined the microscopic structure of these aragonite eyes, comparing them with the surrounding armor structure. They also ran experiments and simulations to reveal that the eyes are more than just light-sensitive spots; they actually resolve images. From more than 6 feet away, chitons can see a blur representing a small fish. This gives them time to clamp down hard on the rock below so the potential predator can't dislodge them, Li said.-Comment: for some reason the retina is not mentioned. Some type is needed. Convergence is a key finding in that needed functions are solved in many ways. Note the bush of life as a proof.