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Operculum: Definition & Types

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

An operculum is a small covering, a lid, or a 'trap door' found on plants or animals. Read this lesson to learn where to find an operculum, as well as what it does!

What is an Operculum?

In biology, an operculum can refer to slightly different things, depending on the organism in question, but in all cases, it is a specialized type of covering that usually protects a sensitive body part. In humans, an operculum can be the mucus plug in the cervix that keeps the contents of the uterus from spilling out after conception, it can refer to a part of the brain, or it can refer to a flap of tissue in the mouth. In animals, an operculum is usually a hard flap or 'trap door' that protects some part of the animal. In plants, an operculum is a flap of some type found on algae, fungi, or vascular plants. As you can see, that is a LOT of diversity for one strange word. So let's investigate further, and see what all the operculum fuss is about.

Human Biology

When referring to the cervical plug required during pregnancy, the operculum has multiple functions. First, it keeps the fluids and tissues in the uterus from spilling out of the body. It also prevents bacteria from passing from the vagina to the uterus, therefore protecting the developing embryo and the mother from infection. The operculum itself not only physically prevents the bacteria from passing, but it also contains antibacterial properties that kill the bacteria upon contact.

The human brain also has multiple opercula, found in the temporal, parietal, occipital, and frontal lobes. These act as forms of protection for extra-sensitive parts of the brain.

The colored regions depict locations of opercula found in the human brain.
Brain opercula

Finally, in dentistry, the operculum is a fleshy tab that forms when a molar is infected or impacted.

Animal Biology

In animals (other than humans), the operculum refers to different structures with different functions. In fish, the operculum is a bony flap covering the gills. It moves back and forth to move water over the gills, allowing the fish to breathe, and also serves as protection against these sensitive parts of the fish.

Some snails have an operculum that acts as a 'trap door' over their opening, allowing them to close up when external threats exist. This can prevent predators from eating them and can keep contaminated water out of their shells until conditions improve.

The red arrow points to the operculum on the snail.
snail operculum

Additionally, some bird species have a bony or hardened operculum covering their nares (similar to nostrils), providing protection and preventing water from getting in while a bird dives for food.

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