Squids are among the most varied and unique of all invertebrates. They are mollusks of the Class Cephalopod, along with the nautilus, cuttlefish, and octopus.Squids are highly evolved, and have developed a number of traits uncommon to most other mollusks. Fossil records of cephalopods have dated back the Cambrian Period (about 600 million years ago).Structurally, squids have only small variations of a basic theme common to all cephalopods. They are spherical or cigar-shaped with two fins used to stabilize movement when swimming. Ten arms are easily distinguished emerging from near the mouthEight of these arms each have four rows of suction cups encircled by rings of chitinous (horny) hooks. These suction cups provide a means of attaching to rocks or holding its food with a powerful grip. The other two arms are called tentacles, and are contractile and longer than the other eight. These tentacles have spatulate tips, which have suckers on their undersides. The contractile tentacles are primarily used to seize prey and pass it to the shorter arms, which hold it at the squid’s beak.The beak of a squid is a very powerful tool shaped like a parrot’s beak, and used for almost the same purpose. With it, squids can easily crack the shells of their prey (which usually consists of crabs or other small animals).A pair of giant eyes can be found near the mouth of the squid. The eyes are fairly complex, which is a trait lacking in most invertebrates. Their structure is similar to that of humans, and comparable in ability.The internal arrangements of squids consist of a mantle that surrounds the body’s organs, as with most mollusks. However, although mollusks are generally characterized as having external shells, most cephalopods contain internal shells, or lack them altogether. Squids have very small shells, called pens, found near center of their bodies.Squids (and cephalopods in general) possess several unusual abil...
