Download Squid Dissection – Information Sheet Squid are made of smaller

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.