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 mouth
Eight 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 havi...
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... are usually seen swimming in large schools. They are capable of great bursts of speed—up to 23 mph, by utilizing a highly advanced form of water-jet propulsion. Of the 375 known species, they can range in size from 8 inches to 60 feet long. It is the largest of all aquatic invertebrates. Depending on the species, squids can live from 1.5 to 3 years.
A highly advanced mollusk of widely varied extremes, squids have proven to be well adapted to their environment, and have carved their own irreplaceable niche into the oceanic community. Squids have always been of major importance to the ecology of the world, and will most likely continue to be so for millennia to come.
1. Grolier 1996 Encyclopedia; Encyclopedia
2. Encarta 1999 Encyclopedia; Multimedia CD-ROM Encyclopedia
3. www.aqua.org; internet website
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