Rotifer

A rotifer is a microscopic creature in the phylum Rotifera. Rotifers prefer calm freshwater environments such as lakes and ponds but can live in saltwater. Although they are tiny, rotifers are multicellular and have enough of a digestive system to be classified as animals instead of plants. In fact, they are the smallest known animals on Earth. There are over 2,200 forms of rotifer. It is unclear how long they have existed. The only part of the animal hard enough to leave a fossil record is the jaw, and the jaw is so small that it is difficult to detect in fossils. However, it is believed rotifers have existed for tens of millions of years. They are important because they provide a food source for creatures like baby fish and coral, which cannot eat larger animals.

Background

The name rotifer comes from the Latin rota, meaning "wheel." The name refers to a wheel-like crown of cilia, or finger-like protrusions, that surround the rotifer's mouth. The rapid movement of the cilia creates the illusion that the cilia is rotating like a wheel. This structure is known as a corona, which assists rotifers in eating.

Antonie van Leeuwenhoek discovered rotifers in the early eighteenth century. Van Leeuwenhoek was an undereducated Dutch merchant who learned to grind glass and made microscope lenses that led to several key discoveries, including blood cells, sperm cells, bacteria, and rotifers.

Overview

Rotifers are so small they are all but invisible without a microscope. They measure about one-twelfth of inch, or two millimeters, in length. Despite their tiny size, they are complex animals. In addition to a full digestive system, they have other internal organs and jaws, which are called trophi. These body parts are often visible when examining the organisms because their skin is usually transparent.

There are three main parts to the rotifer anatomy. A rotifer has a head, a body or trunk, and a foot that is more like a tail, which helps propel the organism through the water. It can also help anchor the animal to surfaces under the water.

Rotifers eat in one of several ways, depending on the species. The cilia that led to their name help them draw food into their mouths. Some rotifers draw in large amounts of water and filter food out of it. Others use the cilia in the corona to hold the food while the trophi grind or chew it. Rotifers are omnivores, meaning they consume both plants and animals. They eat a variety of foods, including algae, bacteria, other small organisms, debris from plants or animals, and even other rotifers.

When it comes to living conditions, rotifers are adaptable. They prefer freshwater sources about the size of a bathtub without any fish, which feed on rotifers. However, they can live in much larger bodies of water. They are also found in much smaller environments, such as wet soil, mosses growing on trees, or small amounts of water in rain gutters and piles of leaves. Rotifers can move about, but they can also live in water that does not allow them much movement. Some rotifers are even capable of existing in very arid environments, such as the desert.

Nearly all rotifers are female. Many species of rotifers are capable of asexual reproduction, which can be accomplished with one single parent organism. For those that require sexual reproduction, the male never eats and does not live long. They exist only to produce sperm to fertilize the females and then die.

Rotifers are capable of adapting this process. In times when water is scarce, females that normally reproduce through sexual reproduction will produce daughters that create their offspring by meiosis, or splitting the eggs. If these eggs are fertilized, they will become females. If they continue to develop without fertilization, they will become males. These males and females can mate to create a special kind of egg known as a quiescent embryo. These eggs can survive without water for years and develop spontaneously once water again becomes available. This allows the rotifer to live even in the desert, where the embryos are made when there is water and then stay in the quiescent embryo state embedded in the dried mud until water is available again.

In addition to the ability to adapt their reproductive methods, rotifers assure their survival by being prolific breeders. A female rotifer can have seven offspring in one day. Those baby rotifers are themselves capable of reproducing within one day. This means that within a week, one single female rotifer can have more than 100,000 descendants.

Rotifers are an important part of the ecosystem. They serve as a food source for many animals. However, rotifers are most crucial for smaller aquatic life, such as baby fish and small crustaceans known as copepods that are too small to eat anything larger than a rotifer. The easily digestible rotifer provides an essential source of nutrition for smaller marine life. They are especially important for coral because they are often the only food that small coral larvae can eat.

Because they are a critical food source for other small aquatic life-forms, rotifers are often cultivated for commercial purposes and sold to people who own freshwater aquariums. Although rotifers themselves are not especially nutritious, they can become good carriers of nutrients when they are fed a healthy diet full of the things that will help young fish, coral, and other life-forms thrive. People who have aquariums where they raise fish and coral often use rotifers to support their aquatic habitats and help all their fish, crustaceans, and coral flourish.

Bibliography

Graves, Jenny. "Instead of Sexual Reproduction, Rotifers Scavenge New Genes from Other Pond Life." Phys.org,15 Apr. 2016, phys.org/news/2016-04-sexual-reproduction-rotifers-scavenge-genes.html. Accessed25 Nov. 2024.

"Introduction to the Rotifera." University of California Museum of Palentology, www.ucmp.berkeley.edu/phyla/rotifera/rotifera.html. Accessed 25 Nov. 2024.

Savard, Chloe. "Rotifers: An Introduction to the Microscopic World of Animals." Discovery Blog, 5 Oct. 2023, www.olympus-lifescience.com/en/discovery/rotifers-an-introduction-to-the-microscopic-world-of-wheel-animals/. Accessed 25 Nov. 2024.

Wright, Jeremy. "Rotifera: Wheel or Whirling Animals." Animal Diversity Web, University of Michigan, animaldiversity.org/accounts/Rotifera/. Accessed 25 Nov. 2024.