Investigation: External Anatomy of a Crayfish

First year biology students explore a variety of animals during dissections and live experiments. Crayfish are an inexpensive way to introduce students to invertebrate morphology.

Students might call this animal other names, such as crawdads, crawfish, or even mudbugs! In this lab, students examine the external anatomy of a crayfish, a member of the Phylum Arthropoda.

Student worksheet includes instructions for locating and identifying external features of the crayfish.

First, students look at the head and mouthparts of the crayfish. The mandible (jaws) of the crayfish open side to side. There are three maxilla which are used to manipulate food. Once students have found the structures, they label a diagram of the head.

Next, students explore the body sections of the arthropod. Crayfish have a cephalothorax (head and thorax) covered by a carapace. The abdomen is segmented, with the final segment containing a fin-like structure called uropod.

Students then examine the appendages of the crayfish. There are four pairs of walking legs and small swimmerets attached to each segment. The largest appendage is the cheliped, or the claw. Students remove the claw and manipulate it to see how how many joints it has.

Finally, students measure the length of each crayfish and compare the size of males to females. Generally, males are larger than females. A short labeling and coloring exercise is included for labeling all of the structures found on the external anatomy of the animal.

Other Arthropod Resources

You can also have students examine the internal anatomy of a crayfish, but this can be difficult. The organs don’t usually preserve well. Also, most of the structures do not have a comparative organ with vertebrates. Crayfish are just weird!