The class cephalopoda, in the phylum Mollusca, includes octopus, squid, cuttlefish and the rare nautilus.  The word “cephalopod” literally means “head-foot.”  As a class in the phylum Mollusca, cephalopods are also related to gastropods (snails) and bivalves (clams, mussels). 

Although cephalopods are in the same class, they look remarkably different from each other.  However, all cephalopods do share several characteristics.  All cephalopods have sucker-bearing arms around the front of their heads – squid and octopus have eight while cuttlefish and nautilus have more. Additionally, squid and cuttlefish have two long tentacles used for grabbing prey.  Cephalopods have highly developed eyes, large brains and a sac from which they discharge a black mucus-bound ink. Ink is used for defense and disguise.  The ink obscures the cephalopod and can irritate the eyes of the predator, which allows the cephalopod time to escape. All cephalopods move by expelling water from a siphon under the head.  Octopods also use their arms to crawl. 

Another characteristic shared by cephalopods is their amazing ability to communicate through the use of chromatophores.  Chromatophores are pigment-bearing cells capable of causing color changes in the cephalopods’ skin by expanding and contracting.  (See http://www.mbl.edu/publications/Loligo/squid/skin.0.html for diagram and animation of chromatophores). The expansion and contraction of the cells is so quick, taking only a fraction of a second, that no other color-change in animals comes near it in speed.  When the chromatophore cell is relaxed, its surface area is small and the color is not visible.  When the muscles contract, the surface area becomes much greater and the color is visible.  Chromatophores can express yellow, orange, brown, red, blue and black. Each chromatophore consists of a bag containing filaments of pigment that are attached to nerve fibers.  The functioning of the chromatophore is all under the control of the cephalopods’ advanced nervous system.  Although cephalopods are known for their large brains, they also have a great deal of local control of their nerves - more than any vertebrate.  Thus, the cephalopods possess incredible control over their chromatophores. 

Cephalopods use their ability for color change in a number of ways.  Along with their ink sacs, they use chromatophores for predator avoidance, either through camouflage or disruptive coloration.  Camouflage can also aid in capturing prey because prey, like predators, are unable to see the cephalopod.  Cephalopods also use their chromatophores to communicate between themselves.  A male cephalopod might display colors as a signal of aggression to another male who seems to be intruding on his mate.  In addition, chromatophores may be used to signal a readiness to mate. (All information in this section comes from Moynihan, 1985.) 

Vocabulary List

Camouflage - concealment by means of disguise; behavior or artifice designed to deceive or hide. 
Cephalopod – the octopods, squids and other mollusks that possess a foot modified into arms that surround the head. 
Chromatophore – a skin cell that contains pigments. 
Disruptive coloration – a color pattern that helps break the outline of an organism. 
Molluscs – the invertebrates with a soft, unsegmented body; a muscular foot; and, with some exceptions, a calcareous shell. 
Tentacle – a flexible, elongate appendage. 

(Definitions from Castro, 2000 and http://school.discovery.com/lessonplans/programs/octopus/)

Video to demonstrate cephalopod color changing (if possible) 

20 pieces of construction paper of at least four different colors 

Use the pictures/overheads and video to lead a discussion on similarities and differences in cephalopods, possibly focusing on the information provided in Background Information (see above).  Depending on your students’ prior knowledge, your introductory presentation on cephalopods and chromatophores can be adapted to meet the interests of your class. 

Before starting the activity, ask students to discuss what cephalopods might try to communicate using their chromatophores.  The activity focuses on predator avoidance, mate recognition, and prey capture, so it is necessary to discuss these particular communications in your presentation.  Because this activity focuses on cephalopods’ use of non-verbal communication, discuss other types of non-verbal communication, such as sign-language and body language. 

(We based this activity on a classroom size of 30 students, but it can be adapted accordingly based on your class size.) 

1. Divide 20 students into 5 groups of 4.  Depending on your class size, groups should range in size from 2-5 students.
2. Gather the remaining 10 students together in one area.  You will be assigning them roles for the activity later.
3. Give each of the 5 groups four different colored pieces of construction paper (e.g. each group will get one piece of red paper, one piece of blue, one piece of yellow, one piece of green).
4. Each of the 5 groups needs to select a group leader. 
5. Explain the basics of the activity to all the students.  The 5 groups will be cephalopods (specify a particular type of cephalopod).  The remaining 10 students will be designated as predators, prey or cephalopod mates.  However, only the group leaders will know which of the students will be predators, prey or mates.   Using the different colored construction paper, the leaders will need to navigate their group through the classroom.  They must avoid the predators while finding a mate and capturing a prey.  Inform students that during the actual game, they will not be able to talk and will only be able to communicate by signaling to each other using the construction paper. 
6. In their groups, the students should decide what they want each color of construction paper to signify.  It is up to the students to decide how to use the paper; they do not have to use all colors.
7. While the groups are discussing, designate the remaining 10 students (from step 2) as predator, prey or mate.  For a group a 10, we chose 2 predators, 4 prey and 2 mates.  Decide on a specific type of predator and prey that would be appropriate to the chosen cephalopod (sharks (predator) and shrimp (prey) work for most cephalopods). 
8. Keep the group leaders, predators, prey and mates inside of the classroom while you briefly send the other cephalopod students out of the classroom.
9. Tell the group leaders which of the students are predators, prey and mates.
10. Those students who are predators should find a place in the classroom from which they cannot move their feet during the actual game.  They can, however, extend their arms to try to catch the cephalopods.  The prey and mates also need to find a fixed spot in the class; however, once they are discovered by a cephalopod, they can move with that group. 
11. The group leaders need to stay in one spot where their group will be able to see their signals.
12. Let the cephalopod students back into the classroom.  Explain that from this point on there will be no talking.  Each group will need to stick together and will need to pay attention to their group leaders who will signal to them from their spots to show them which students they should avoid (predators) or try to find (prey and mates).  Tell them to carefully observe their group leaders because predators will be able to extend their arms and if a predator touches them, their entire group will be eliminated.  It is also possible to eliminate just those cephalopods touched by the predator, which allows the remaining group to continue.
13.  Let the game run 5 minutes, or until all prey and mates have been captured by the groups.
14. After the activity, have students return to their seats for discussion.
15. Immediately after the activity, before discussion questions, it is interesting to discuss the results such as which groups were most successful or unsuccessful and what the groups used the colors to mean.
16. The activity can be repeated which should allow students to get increasingly better at using the colors to communicate. 

All images can be used for educational purposes. 

Two Pacific Reef Squid, Sepioteuthis lessoniana, photographed at night in the Red
 Sea.

The Red Octopus, Octopus rubescens. 

The chambered Nautilus, Nautilus pompilius. This specimen was trap caught at depths
of 200-300m in the Phillipines. 

A courting pair of European Cuttlefish, Sepia officinalis. The male (foreground) is
 guarding the female (background) from other males. These are fully mature animals at
 about one year of age. Note the bold zebra-like striping typical of this species.

1. What are some of the problems that you faced in communicating during the activity?
2. What is an adaptation that cephalopods possess to aid in their communication and why is it an advantage for them?
3. What types of things do cephalopods express using their chromatophores?
4. What are some other forms of non-verbal communication?