Objectives:

• The student will be able to identify characteristics of cephalopods by comparing gross anatomical structures of squids and octopuses.

• The student will be able to place cephalopods in their major group, or phylum.

Materialas:

• Mission Impossible music (optional)
• pictures of squid and octopus
• actual specimens of the above (optional)
• graphic organizer on which to record information (See example below.)

Procedure:

1. Play Mission Impossible music to pique the students' interest. Tell the students that their mission is to examine two cephalopods, the squid and the octopus. The students will be detectives and have to discover the identifying clues that were used to classify these animals as cephalopods. In other words, they will have to examine both animals and identify the characteristics that they have in common which make them both cephalopods. Then the students need to find what makes the squid and the octopus different.

2. Students, either as individuals or as groups, are given pictures of squids and of octopuses. (Option: Give the students actual specimens. If not enough specimens are available, students may work in groups or in pairs. The grocery store or fish market would be a good source for specimens.)

3. Students are to brainstorm characteristics of these animals that they plan to compare. The teacher can write these characteristics on the board. Students, as a class, then should identify the ones they feel are most important and list them on the graphic organizer. (Option: Let students identify characteristics on their own as a small group or individual assignment and list these on the chart.)

   Some characteristics that the students might list are: color, presence or absence of tentacles, arms, size, weight, eyes, texture of skin, suckers, body arrangement, mouth and beak, shell or skeleton.

4. Students need to examine their specimens with regard to the listed characteristics, filling in the chart as they look at each creature. They are searching for characteristics that the two cephalopods have in common and for features that are different.

5. The teacher can draw a large chart, similar to the students' lists, on the board. The students share their information about their findings and the teacher records this information on the chart.

6. From the combined information, the students then write a "detective's report" in which they compare the likenesses of the two animals. They need to state why these particular likenesses are important to classify these animals as cephalopods. For example, both animals have arms with suckers. This is important because most animals such as fish and birds do not have arms or suckers. Therefore, the arms show a relationship between the two animals. However, students need to note that although both squids and octopuses have arms, these arms are arranged differently on the two animals. Some characteristics will not be important, and the students need to state this. For example, the size of the specimens may not be an important likeness for comparison as many animals may be the size of the specimens. One can not judge the size of all squids and octopuses by two samples.

7. Have a student look up the definition of cephalopod in a zoology book, a science book, or on the Internet. Did the definition of a cephalopod mention the same characteristics that the students chose? What phylum do cephalopods belong to? Can you find the molluscan characters? What other animals are mollusks? Did the students correctly complete Mission Cephalopod?

   Comparison of Squid and Octopus (Example)
   Characteristics	Squid	Octopus
   appendages	8 arms, 2 tentacles	8 arms, 0 tentacles
   suckers	yes (May describe what they look like and the location of the suckers on arms and tentacles.) Look for rings around suckers rims.	yes (May describe what they look like and the location of the suckers on the arms.) They have no rings.
   external shell or skeleton internal support	no one gladius present	no two tiny stylets may be present (They are often difficult to find. One would have to dissect the mantle and find the stylets embedded in muscle.)
   eyes	two (May describe what they look like and the location of the eyes.)	two (May describe what they look like and the location of the eyes.)
   body arrangement	part containing the head, part containing the arms, part containing the organs called the mantle (3 parts)	part containing the head, joined to the part containing the arms, the mantle (3 parts)
   color	white, pink, gray (whatever color the specimen is)	gray, white (whatever color the specimen is)