Activity: Bivalve Senses

Humans and vertebrate animals use their senses, in varying degrees, to explore their environment, avoid danger, and even learn. The five main senses are hearing, sight, smell, taste, and touch. Some species have evolved additional senses such as echolocation in bats and electroreception in sharks.

It might be surprising to learn that these senses are also found in many invertebrate animals, including bivalves. An invertebrate might not have eyes or ears that look like ours but it might have another kind of sense organ that accomplishes the same thing. Some of the senses might be absent or poorly developed but others might be more sensitive than in human senses. The strengths of the senses will depend upon the type of bivalve you test but, in general, it is believed that touch is the most developed, followed by sight, smell, taste, then hearing.

Ask your students to design experiments to test the senses of bivalves living in your classroom aquarium. Click here for information on how to maintain bivalves in the classroom. The reactions can vary between bivalve species (adaptationsAdaptation:
The evolutionary process through which a population becomes better suited to its environment over many generations of natural selection.), but can also vary among individuals (variationVariation:
The differences among individuals in a population.). These species adaptations and individual variations will provide clues to the evolutionary past and potential evolutionary future.

Please be creative and have fun with the experimental design and testing (but please caution your students to be gentle — these are living animals). If you have access to other types of invertebrates (snails, starfish, etc.), include those too in the tank and see how their reactions differ from those of the bivalves. Here are a few suggestions and hints to get you started:

• Touch: Gently touch different parts of the bivalves (shell, edge of the mantle, siphons, etc.) and observe or measure the reactions. [Hint: Bivalves are very sensitive to touch and usually clamp shut at the slightest touch anywhere.]
• Smell: Place a small piece of different kinds of food in different areas of the tank (away from the bivalves) and observe or measure the reaction. [Hint: Bivalves probably will not respond to this at all. Most bivalves are filter feeders and do not need an acute sense of smell to detect food. Contrast this with a carnivorous snail or starfish.]
• Taste: Provide different foods directly to the bivalves and observe or measure the reaction. [Hint: Bivalves probably will not respond to this at all. There are very few bivalves that detect and eat food or prey near them.]
• Sight: Move your hand or another solid object over the bivalve, creating a shaded area, and observe or measure the reaction. [Hint: Some bivalves have primitive eyes, actually photoreceptors that can detect light and dark, as an anti-predator mechanism. Some bivalve eyes actually have lenses, but the degree to which they can “see” in the way that humans can is uncertain.]
• Hearing: Expose the tank to different frequencies and volumes of noise and observe or measure the reaction. [Hint: Bivalves do not have ears, however, sound is really vibrations in the air. Water movement is another form of vibrations, and can be detected by a bivalve in the same way that touch is detected.]