One small group of very strange squid prowls the mid-depths where light levels are very weak and being spotted by sea lions or toothed whales means a certain death. To avoid detection the glass squids ('cranch' squids) have learned to become invisible.
Most of the 60 species are transparent giving them their name. Some even have light organs to cancel out shadows cast by their eyes. Their digestive glands are visible but usually held vertically to cast the smallest shadow.
Some eyes are small and circular but a few species have eyes like ‘telescopes’ that can be extended away from the body. Scientists have no explanation for the telescopic eyes.
Most glass squid are small with rounded bodies but one species, the Colossal Squid, is the largest of all squid species reaching 14 metres in length and 500 kg.