Cephalopods E.L. To gain a better understanding of the class Cephalopoda and the organisms that are part of it

First, why are cephalopods interesting? Cephalopods can change color faster than a chameleon They can also change texture and body shape If those camouflage techniques don't work, they can still "disappear" in a cloud of ink, which they use as a smoke-screen or decoy Cephalopods have three hearts that pump blue blood They move by jet propulsion of water They are found in all oceans of the world

Cephalopods

What is a cephalopod? Cephalopods are invertebrates of the class Cephalopoda, which is within the phylum Mollusca (the molluscs) The class Cephalopoda is made up two subclasses: Nautiloidea containing the pearly nautilus, and Coleoidea containing the squids, cuttlefish, and octopus cuttlefish squid octopus nautilus

What is a cephalopod? Scientists believe that the ancestors of modern cephalopods (squid, octopus and cuttlefish) diverged from the primitive externally-shelled Nautilus possibly as long ago as 438 million years. This was before the first mammals appeared, before vertebrates invaded land, before there were fish in the ocean and before there were upright plants on land

What does cephalopod mean? Cephalopod means ‘head foot’. The feet, or arms, of these creatures are connected to their heads, not their bodies. The rest of the body is in front of the head. That's why they're called, "head-footed.” In order to be classified as a cephalopod the organism must contain the following: Bilateral body symmetry A prominent head A set of arms or tentacles modified from the primitive molluscan foot Cephalopods also have well-developed senses and large brains- unlike most molluscs.

Cephalopods There are four main types of cephalopod: the nautilus (subclass Nautiloidea) the cuttlefish, the octopus and the squid (subclass Coleoidea) Each type has its own unique features that have helped informed their classification by scientists

Nautilus Unique features: Only subclass of the cephalopods to have an external shell A nautilus' tentacles are also different from those of an octopus or a squid: they are not equipped with suckers. Instead, sticky cilia make adhesive pads, that ensure safe hold on the prey.

Cuttlefish Unique features: The shell in cuttlefish is internal and is called the cuttlebone. The cuttlebone provides the cuttlefish with buoyancy, which it regulates by changing the gas-to-liquid ratio in the chambered cuttlebone using the siphon. Cuttlefish have eight arms and two tentacles like the squid. Cuttlefish can move by jet propulsion but their hovering and normal swimming is achieved by gentle undulations of their lateral (side) fins. Random fact: You have probably seen the ‘cuttlebone’ being sold in pet stores as a source of calcium for birds

Octopuses and squids Octopuses and squids have hard, parrot-like beaks. Octopuses and squids move by "jet propulsion", sucking water into a muscular sac in the mantle cavity surrounding their bodies and quickly expelling it out a narrow siphon.

Squid Unique features: A squid has ten arms like a cuttlefish (an octopus has eight): eight of the same length and two extra long ones used in grabbing prey. The arms of squid and octopuses are different. Squids have extra armature-hooks on the sucker rings. This allows for them to grasp hold of their prey. Triangular head, with two fins on it Squids possess a reduced internal shell known as a pen that acts as a flexible backbone Scary fact: The arms of a giant squid can be up to 3 meters in length, while its tentacles can be up to 10 meters long!!

Octopus Unique features: An octopus has eight arms Rounded head Octopuses no longer have any remnant of a shell

How do scientists classify things? A dichotomous key is a series of questions which leads to the identification of an item- whether a living organism or inanimate object. It is a method for determining the identity of something (like the name of a butterfly, a plant, a lichen, or a rock) by going through a series of choices that leads the user to the correct name of the item. Dichotomous keys can be created to be graphical using a branched/tree like design, but can also simply be a list of questions.

Examples of dichotomous keys drawn using the tree design A more complicated dichotomous key A very simple dichotomous key

An example of a more creative key

How do they work? At each step of the process of using the key, the user is given two choices; each alternative leads to another question until the item is identified. E.g. A question in a dichotomous key for trees might be something like, "Are the leaves flat or needle-like?" If the answer was "needle-like," then the next question might be something like, "Are the needles in a bunch or are they spread along the branch?" Eventually, when enough questions have been answered, the identity of the tree is revealed.

Examples of dichotomous keys as simple lists ^ a bit of a silly one about candy (with made up scientific names for the lollies)

Make your own Dichotomous key Option 1 As a simple example, you can construct a dichotomous key to identify people (or another group of items) in a classroom, using questions based on gender, hair length/color, glasses (or not), clothing color, etc. Question 1: Is the person male or female?
 Question 2: Does the person wear glasses or not?
 Question 3: Is the person wearing blue jeans or not? The end of each branch or series of questions of the key should be a person's name. A dichotomous key will have enough questions to identify each member of the group. To test it, you can identify each person in the group by going through the key and seeing if the right name comes up.

Make your own Dichotomous key Option 2 Come up with an imaginary species, for example a species of odd looking aliens with a varying number of body parts. Draw at least ten of these creatures, showing their distinctive features that you are going to use to classify them. Create a dichotomous key classifying the new species, for example: Question 1: Does the creature have legs? Question 2: Does the creature have antenna? Question 3: Does the creature have two eyes?

Lesson work In your books answer the following questions: What are the distinguishing features of the members of the class Cephalopoda? What are the different subclasses within the cephalopod class? Name any distinguishing features of the creatures in these subclasses. Attempt one of the options outlined in this PowerPoint for making your own dichotomous key. Using your knowledge of the different subclasses within the cephalopod class, have a go at making a dichotomous key that could be used to identify which subclass within Cephalopoda a creature belongs to. Imagine you found a creature on the beach, what questions would you ask to find out what type of cephalopod it was? Remember the questions can only have two options for answers- yes and no questions are a good method to start with

Some links http://www.thecephalopodpage.org http://tolweb.org/treehouses/?treehouse_id=4225