The squid is part of the mollusk phylum, the largest of the marine phylum. Specifically, squid are cephalopods, of the subclass Coleoidea. Within this subclass, containing over 700 species, the squid has three close relatives: the octopus, the cuttlefish and the vampire squid. In addition to these close relatives, the squid also has many distant relatives, including members of the gastropod and bivalve classes of mollusks.
Close Relative of the Squid: the Octopus
Octopuses, members of the octopoda order, are close relatives of the squid. Like the squid, octopuses have eight arms covered with suckers. Unlike the squid, these suckers do not contain hooks. Octopuses have a large mantle, but lack any internal shell. These creatures use pigments to camouflage themselves and release defensive ink, just as the squid does. Octopuses also share the squid's high-level of intelligence, showing the ability to problem-solve and demonstrating short- and long-term memory capabilities. Like the squid, octopuses use mantle-generated jet propulsion to move.
Close Relative of the Squid: the Cuttlefish
Cuttlefish, members of the sepiida order, have a soft body, with a type of backbone. This backbone was originally a form of shell that has become internalized. Like all cephalopods, the cuttlefish also has eight sucker-covered arms. The cuttlefish can use mantle-generated jets to make rapid movements, or it can use its side-fins to make more gentle moves. This creature can also use internal gas pockets to change its buoyancy. The cuttlefish is very intelligent, possessing a highly complex, donut-shaped brain. Like the squid, the cuttlefish can also release defensive ink and uses pigments for camouflage.
Close Relative of the Squid: the Vampire Squid
Vampire squid, members of the vampyromorphida order, are very similar to squid, which are members of the teuthida order. Vampire squid share the eight, long, sucker-covered arms that are common to all cephalopods. Like the squid, they also feature two retractable tentacles and a set of fins on their mantle. The vampire squid gets its name from their jet-black skin, webbing between arms and red eyes. The vampire squid's eyes are, proportionally, the largest eyes of any animal in the world. These sea creatures have photophores over their entire body, which they use to produce a luminescent glow. While they have lost their ink sack, they can expel a mucus cloud that contains glowing particles. Like all cephalopods, they do possess chromatophores for camouflaging; however, they are nonfunctioning. This lack of functionality is due to having lost the muscle that is used to control the color changes.
Distant Relatives of the Squid
While its close relatives are cephalopods and members of the same coleoid subclass, the squid also has many distant relatives within the mollusk phylum. These distant relatives include gastropods and bivalves. The gastropod class contains snails and slugs. The bivalve class includes scallops, oysters, clams and mussels. All of these mollusks share a broad, muscular foot; however, in cephalopods, this foot has evolved into their eight arms.
- Smithsonian Natural Museum of Natural History; Cephalopods in Action
- Tree of Life; Cephalopoda; Richard E. Young, et. al.
- The Cephalopod Page; Selected Cephalopd Species; James B. Wood, Ph.D.
- Animal Diversity Web; Octopus Vulgaris; Robin J. Case
- Octopusworlds; Octopus Facts and Information
- Government of South Australia PIRSA Fisheries; Cuttlefish
- Photo Credit Jupiterimages/Photos.com/Getty Images
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