Glow-in the-dark squid? Plus, what’s the amazing, vicious difference between squid and octopi? On a recent expedition to explore the seamounts in the southern Indian Ocean by scientists, a new species of large squid was discovered. A specimen of the new species, which can grow up to 30 inches long, belongs to the deep-sea Chiroteuthid family, which are known for being radically bioluminescent (naturally glowing.) Don’t confuse this squid with the squidworm, a creature also just discovered that is so unusual that it requires a brand new genus. This lovely squid find sparked a common question regarding squids and octopi (or octopuses, both plural forms are correct.) How do the two marine creatures differ? Both tentacled types have a ton in common. They both live in salt water and are related to snails. They both move by jet propulsion and have hard beaks that are used to rip away the flesh of their prey. Neither animal produces poison that can harm humans. (The blue ringed octopus is an exception.) Expelling ink is a shared defense against predators. And both creatures, amazingly, have blue blood. (Speaking of blood and the ocean, researchers also recently announced the discovery of a critter called the “Dracula fish.” Learn the reason behind the grim name, here.) While both species are related to mollusks, octopuses have no remnant of a shell. On the other hand, squids have a pen, a stiff structure that acts like a flexible backbone. Squids and octopuses both have eight arms lined with suckers. But squids have two additional, prey-capturing tentacles that can be compared to implements from a horror film. Their diets are also different. Octopuses feast on bottom-dwelling crustaceans, while squids eat fishes and shrimps. And, while squids live in schools in the open ocean, octopuses reside alone in sea floor dens.