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Squid Dissection – Information Sheet Squid are made of smaller parts which are organized by shape and purpose. These layers of organization include cells, tissues, organs, organ systems, and the whole organism. Can you identify a squids structures and their functions? Background The squid is one of the most highly developed invertebrates. Squid can be as small as a thumbnail, or as large as a house. The giant squid, Architeuthis, can measure 60 ft. in length and weigh three tons! Squid are an important part of the ocean food web. Squid are a major food source for many fishes, birds and marine mammals. They are also gaining popularity as a food source for humans around the world. Overfishing is a growing concern because there are no regulations on squid harvesting. Squid are seined commercially at their spawning grounds. About 6,000 metric tons are taken yearly for human food and bait. After mating, a female squid will produce 10-50 elongated egg strings, which contain hundreds of eggs each. In many species, the parents will soon die after leaving the spawning ground. The egg strings are attached to the ocean floor, are left to develop on their own, and hatch approximately ten days later. Southern California squid populations spawn mainly in the winter (December to March). External Structures Some of the animal’s structures show the ways in which the squid has adapted to life in the ocean. It has a streamlined body with fins at one end for steering, and “jet propulsion.” Jet propulsion occurs as the squid squeezes water out of its body through its siphon. This adaptation makes the squid a fast, active predator. This animal also has a very good defense mechanism. Squid produce a dark ink that they use to escape from predators. When a squid is startled, the ink is released through the anus, and the cloud of inky water confuses the predator while the squid swims away. Squid also have chromatophores, which are pigmentcontaining and light-reflecting cells, or groups of cells that the squid can use to camouflage with it’s environment. Squid have ten arms, which are wrapped around the head. Eight are short and heavy, and lined with suction cups. The ninth and tenth are twice the length of the others, and are called tentacles. Suction cups are only on the flat pads at the end of the tentacles. Squid feed on small crustaceans, fish, marine worms, and even their own kind! They use their tentacles to quickly catch their prey, which is pulled in by the arms and down to the radula, or beak, which uses a tongue-like action to get food to the mouth so it can be swallowed whole. Squid have a soft body which has a special covering called the mantle, which encloses all of the body organs such as heart, stomach, and gills. Squid Dissection – Information Sheet Internal Structures Compared to other mollusks, the squid has a relatively complex circulatory system (a closed circulatory system) The squid has gills which absorb oxygen from the water and eliminate carbon dioxide, similar to our lungs. At the base of each gill is a gill heart which sends deoxygenated blood through the gills. Once the gills have supplied this blood with oxygen, the systemic heart (found below the kidney) pumps the oxygenated blood throughout the body. The kidney filters waste out of the blood. Squid have a one way digestive tract, similar to humans. Food enters through the mouth and is broken down first by the “beak”. A digestive gland, located just dorsal to the siphon secretes digestive juices to help break food down. The esophagus goes directly through this digestive gland. Food passes through the esophagus which carries it all the way to the stomach. (found under the gonads) After leaving the stomach food passes into the intestine which carries waste to the anus to be eliminated from the body. Just anterior to the systemic heart, you can see the ink sac which store ink to be released as a defense mechanism. At the posterior end of the squid you can find the gonads. In male squid the testes produce sperm. In female squid the ovaries produce eggs. The squid is supported as it speeds through the water by a stiff structure called a pen. This structure is the remnant shell. The pen is as long as the length of the mantle and shaped like a transparent feather.