Cuttlefish start watching the world, and possibly picking prey, before they hatch
A cuttlefish's eyes appear to be fully formed before it leaves the egg, and the embryo starts looking around from inside. Hatchlings may then prefer to hunt whatever prey they saw beforehand. For an animal that usually lives only one or two years, getting an early look may be worth a lot.
Those eyes are strange in other ways too. The pupil is a smooth W shape. Cuttlefish are colour-blind but can detect polarised light, which sharpens contrast, and each retina has two concentrated patches of sensors, one aimed forward and one back. They focus by sliding the whole lens rather than reshaping it, and because the optic nerve runs behind the retina, they have no blind spot. Similarities to our own eyes arose independently.
Inside the body sits the cuttlebone, a porous, chambered internal shell made of aragonite. By adjusting the balance of gas and liquid in its chambers, the animal controls its buoyancy. Each species has a cuttlebone of distinctive shape and texture, and among the related squids and octopuses only one other group keeps a chambered shell like it.
Cuttlefish usually measure 15 to 25 centimetres, though the giant cuttlefish reaches 50 centimetres in mantle length and over 10.5 kilograms. They hunt crabs, shrimp, fish and even one another, gripping prey with two long tentacles beyond their eight arms. Threatened, one can gulp water and spread its arms to look bigger. Fins do most of the steering. For their size they have some of the largest brains of any invertebrate and rank among the cleverest.
Greeks and Romans prized the brown ink they squirt when alarmed, and the Greek and Latin name for the animal, sepia, became the English word for that reddish-brown colour. The English cuttle comes from Old English cudele. The oldest known fossils date from the very end of the Cretaceous, found in the Netherlands.
Source: Cuttlefish
