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Planogyra asteriscus

What do they look like?

The Eastern flat-whorl is a tiny brown land snail with a flattened spiral shell that is about 1.8 mm in diameter and 0.9 mm tall. The shell spirals to the right, and usually has 4 spirals. The shell is a pale brown color and is slightly see-through. The opening of the shell is round and thin. The part that is outside of the shell that the snail moves around on is called the foot, and it is strong and muscular. Like all snails, Eastern flat-whorl snails go through a process called torsion. Torsion causes the main body mass to rotate so that the anus is located at the front of the body near the head.

Eastern flat-whorl snails look very similar to another snail, Vallonia costate. You can tell them apart by the lighter color and thicker shell opening of Vallonia costate. ("Rare Species Explorer", 2007; Nekola, 2003; Ogle, 2007)

Where do they live?

Planogyra asteriscus, the Eastern flat-whorl snail, can be found in ten north-eastern and mid-west states in the United States. It is also present in Canada. It is found from Newfoundland west through New York, Ohio, and Ontario to northeastern Minnesota. ("Distribution and ecology of terrestrial gastropods in northwestern Minnesota", 2002; Cordeiro, 2013; "Michigan Natural Features Inventory Planogyra asteriscus (Morse) Eastern flat-whorl State Distribution", 2008; Nekola, 2003; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

What kind of habitat do they need?

The Eastern flat-whorl snail is a land snail that lives in hardwood forests, wetlands, lake shores, and fen habitats. The Eastern flat-whorl snail has is often in lowlands that have many northern white cedar trees. ("Distribution and ecology of terrestrial gastropods in northwestern Minnesota", 2002; Cordeiro, 2013; Nekola, 2003)

How do they grow?

The Eastern flat-whorl snail lays its fertilized eggs into a moist hole, where the offspring will develop. While still in the eggs, the offspring will go through two larval stages and a metamorphous. The first larval stage is called a trochophore stage, which is a free-swimming individual covered in little hairs called cilia. The second larval stage is called a veliger, which is when it starts to look like a snail. The veliger still has cilia but starts to develop a shell. The final stage in the egg is when the veliger develops into a juvenile snail. This development is called metamorphous. The juvenile snail hatches from the egg about 25 days after the eggs were first laid. (Ogle, 2007)

How do they reproduce?

Eastern flat-whorl snails are hermaphrodites, meaning that each snail has both male and female reproductive parts. In a single snail, the sperm develops much earlier than the eggs, so the sperm is gone by the time the eggs develop, which prevents a snail from fertilizing itself. Many land snail species have elaborate courtship behaviors that take place between two snails before mating. When mating, each Eastern flat-whorl snail transfers sperm to the other snail. (Ogle, 2007)

After two snails transfer sperm to each other and the eggs are fertilized, the snail lays its fertilized eggs into a moist hole where the offspring develop inside the egg. The young do not emerge from the egg until they have developed into juveniles, about 25 days later. There is little else known about the reproduction of Eastern flat-whorl snails. ("Michigan Natural Features Inventory Planogyra asteriscus (Morse) Eastern flat-whorl State Distribution", 2008; Nekola, 2003; Ogle, 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

Eastern flat-whorl snails place their eggs in moist holes, which provides a safe environment for the egg while the offspring develops inside. The egg itself also has a fluid filled environment where the offspring can go through several developmental stages inside. After the eggs are laid, the parent snail does not return to provide any more care. (Ogle, 2007)

  • Parental Investment
  • pre-hatching/birth

How long do they live?

It is not known how long Eastern flat-whorl snails live.

How do they behave?

Eastern flat-whorl snails have been reported to prefer moist soils, cool temperatures, and high relative humidity. These snails have a muscular foot, which they use to move on by expanding and contracting the muscles in the foot. The foot also contains glands that produce mucus and creates a trail of slime as it moves along. The slime makes the ground slipperier and allows the snail to move along easier. ("Rare Species Explorer", 2007; Ogle, 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

How do they communicate with each other?

Eastern flat-whorl snails have retractable tentacles on their head that they can extend or pull back into their bodies. Their eyes are located at the top of these tentacles. They can also smell through these tentacles. ("Michigan Natural Features Inventory Planogyra asteriscus (Morse) Eastern flat-whorl State Distribution", 2008; Nekola, 2003; Ogle, 2007)

What do they eat?

Eastern flat-whorl snails mainly eat plant material. They eat leaves, mosses, algae, lichens, fungi, and a little bit of soil. (Ogle, 2007)

  • Animal Foods
  • terrestrial worms
  • Plant Foods
  • leaves
  • roots and tubers
  • fruit
  • flowers
  • bryophytes
  • lichens
  • algae

What eats them and how do they avoid being eaten?

Land snails have a large number of natural predators, such as birds. They also often get infected with parasites. They are able to pull the soft parts of their body into their shell to protect it from predators. (Ogle, 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

  • Known Predators

What roles do they have in the ecosystem?

Eastern flat-whorl snails are an important part of their ecosystem. They are eaten by a variety of predators. They also cycle calcium through the environment. Land snails often have parasites living in their bodies, and when a bird or mammal eats the snail, the predator will get infected with that parasite. (Ogle, 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

Do they cause problems?

Eastern flat-whorl snails do not cause any problems for humans.

How do they interact with us?

Eastern flat-whorls snails do not have any positive effects on humans.

Are they endangered?

In Minnesota and Michigan, Eastern flat-whorl snails are considered a species of special concern. While not yet endangered, their populations are threatened and need to be watched closely to make sure they do not disappear. The main threat for these snails is habitat destruction. Since they cannot move very far, if their habitat is changed or destroyed, they cannot move to a new habitat and will die. People need to be careful about what effect their daily activities have on the environment and the animals that live there. ("Distribution and ecology of terrestrial gastropods in northwestern Minnesota", 2002; "Rare Species Explorer", 2007; "Minnesota Administrative Rules", 2013; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)


Kyle VanVleet (author), Minnesota State University Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Angela Miner (editor), Animal Diversity Web Staff.


Minnesota Department of Natural Resources. Distribution and ecology of terrestrial gastropods in northwestern Minnesota. 6136. St. Paul: Minnesota Department of Natural Resources. 2002. Accessed March 14, 2014 at

Wisconsin Department of Natural Resources. 2014. "Eastern Flat-whorl (Planogyra asteriscus)" (On-line). Accessed March 14, 2014 at

Michigan State University Board of Trustees. 2008. "Michigan Natural Features Inventory Planogyra asteriscus (Morse) Eastern flat-whorl State Distribution" (On-line). Accessed March 14, 2014 at

The Office of the Revisor of Statutes, State of Minnesota. 2013. "Minnesota Administrative Rules" (On-line). Accessed April 22, 2014 at

2007. "Rare Species Explorer" (On-line). Michigan Natural Features Inventory. Accessed March 27, 2014 at

Cordeiro, J. 2013. "Planogyra asteriscus" (On-line). Nature Serve Explorer. Accessed April 25, 2014 at

Nekola, J. 2003. Terrestrial gastropod fauna of Northeastern Wisconsin and the Southern Upper Peninsula of Michigan. AMERICAN MALACOLOGICAL BULLETIN, 18: 21-44. Accessed March 14, 2014 at

Ogle, M. 2007. "Planogyra asteriscus" (On-line). Accessed April 19, 2014 at

University of Michigan Museum of ZoologyNational Science Foundation

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VanVleet, K. 2014. "Planogyra asteriscus" (On-line), Animal Diversity Web. Accessed April 20, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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