Squid Dissection – Information Sheet
Squid are made of smaller parts which are organized byshape and purpose. These layers of organizationinclude cells,tissues, organs, organ systems,andthewhole organism. Can you identify a squids structures and their functions?
Background
The squid is one of themost highly developedinvertebrates. Squid can be as small asa thumbnail, or as large as ahouse. The giant squid,Architeuthis, can measure 60 ft. inlengthand weigh three tons! Squid are an important part of the ocean food web. Squid are a major food source for manyfishes, birds and marine mammals. Theyare 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 commerciallyat their spawning grounds. About 6,000 metric tonsare taken yearly for human food and bait.After mating,afemale squid will produce 10-50 elongated egg strings,whichcontainhundreds ofeggs 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.SouthernCalifornia squid populations spawn mainlyinthewinter (December toMarch).
External Structures
Some of the animal’s structures show the ways inwhich the squid has adapted to life intheocean. It has astreamlined body with fins at one end for steering,and “jet propulsion.” Jet propulsion occurs as the squid squeezeswater out ofits bodythrough itssiphon. This adaptation makes the squid a fast, active predator. This animal alsohas a very good defensemechanism.Squid produce a dark ink that theyusetoescape from predators. When a squid is startled,the ink is released through theanus,and the cloud of inky water confuses the predator while the squid swims away. Squid also have chromatophores, whicharepigment-containing and light-reflectingcells, or groups of cells that the squid can use to camouflage with it’s environment. Squid have tenarms,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 calledtentacles.Suctioncups are onlyon theflat pads atthe end ofthe tentacles. Squid feed onsmall crustaceans, fish, marineworms, and even their own kind! They use their tentacles to quickly catch their prey, which is pulled inby the arms and downtotheradula, or beak, which uses atongue-like action to get foodto the mouth so itcan be swallowed whole. Squid havea soft body which has a special covering called themantle,which encloses all of thebody organs such asheart,stomach, and gills.
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.