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Planogyra asteriscus

By Kyle VanVleet

Geographic Range

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. Its range extends from Newfoundland west through New York, Ohio, and Ontario to northeastern Minnesota. It is native to the Nearctic range. ("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)

Habitat

Planogyra asteriscus generally inhabits hardwood forests, wetlands, lake shores, and fen habitats. It is not found in sphagnum-dominated wetlands. The Eastern flat-whorl snail has commonly been reported to occur in lowlands that support northern white cedar trees. ("Distribution and ecology of terrestrial gastropods in northwestern Minnesota", 2002; Cordeiro, 2013; Nekola, 2003)

Physical Description

Planogyra asteriscus is a tiny brown land snail with a flattened spiral shell that is approximately 1.8 mm in diameter and 0.9 mm tall. The shell of the Eastern flat-whorl snail is dextral and has about four whorls with oblique ribs that are regularly spaced and displaying growth lines between them. The shell has thin ribs with sharp edges that protrude from the shell as they spiral around the outer whorl. The shell is a pale brown color and is marginally translucent and has noticeable spiral lines. The aperture of the shell is round, thin and oblique. Like all gastropods, the Eastern flat-whorl snail snail goes through torsion. The torsion process involves the visceral mass rotating so that the anus is located in the anterior portion of the body. Planogyra astericus has a large muscular foot, which it uses for locomotion.

The shell of a Vallonia costate is very similar to that of the Eastern flat-whorl shell, with the major difference being lighter in color and a thickened lip on the aperture. There are other noticeable differences between the Vallonia costate and the Eastern flat-whorl snail, such as the ribs on the shell of the Vallonia costate are smoother and more regular. ("Rare Species Explorer", 2007; Nekola, 2003; Ogle, 2007)

Development

The Eastern flat-whorl snail lays its fertilized eggs into a moist hole; it is there that the progeny go through direct development. The progeny go through two larval stages and a metamorphous while still inside the egg, because water may not be accessible. The first larval stage the snail goes through is called a trochophore stage (a free-swimming ciliated individual). The second larval stage the snail goes through is called veliger (this is when the individual start to resemble a snail). While in the veliger stage, the individual still has cilia, but is also starting to develop a shell and a large proportion of its internal adult organs. The final development stage (while in the egg) is accomplished when the individual goes through metamorphous, a process in which the individual matures into a juvenile snail. The juvenile snail emerges from the egg approximately 25 days after the eggs had been laid. (Ogle, 2007)

Reproduction

Eastern flat-whorl snails are hermaphroditic, as they have both female and male sex organs. However the sperm develops much earlier than the eggs, to assure self-fertilization does not occur. This way the individual’s sperm is gone by the time their eggs mature, and the sperm from a separate individual can fertilize those eggs. Land snails commonly express elaborate courtship behaviors, though they are unknown for this species. When mating, Eastern flat-whorl snails transfer sperm cells from one individual to another through a spermatophore. Two individual snails are capable of transferring sperm to each other simultaneously. (Ogle, 2007)

The reproduction process of land snails, like Planogyra astericus, is characterized by internal fertilization. After sperm transfer, 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 gone through significant development 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, providing a suitable environment for the egg to survive and the offspring to develop. The egg itself also contains an fluid filled environment that allows for development inside the egg. However, this is no other parental care provided. (Ogle, 2007)

  • Parental Investment
  • pre-hatching/birth

Lifespan/Longevity

The lifespan of Planogyra asteriscus is not available in the literature.

Behavior

Observation of the Eastern flat-whorl snail is mostly documented in the growing season, and more specifically following rain showers. Eastern flat-whorl snails have been reported to have a predilection for moist soils, cool temperatures, and high relative humidity. Planogyra astericus has a muscular foot, which it is able to expand and contract for means of locomotion. The snail’s muscular foot contains mucus glands which secrete a slime trail, making it easier for the snail to move on rough grounds. ("Rare Species Explorer", 2007; Ogle, 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

Communication and Perception

The Eastern flat-whorl snail belongs to the order Stylommatophora, individuals of which commonly have retractable tentacles. These retractable tentacles, which contain the eyes at the end of them, are located on the anterior portion of the snail’s body. Their sense of smell is also perceived by their tentacles. ("Michigan Natural Features Inventory Planogyra asteriscus (Morse) Eastern flat-whorl State Distribution", 2008; Nekola, 2003; Ogle, 2007)

Food Habits

The diet of land snails encompasses a wide range of organic materials such as plants, soil, animal tissue, and fungi. Planogyra astericus prefers senescent plant material over green or dead plant tissue. Land snails, in general, have been reported to eat mosses, algae, and lichens; however it is highly uncommon for them to eat grasses. It is likely that these snails prefer senescent plant tissue because of its generally low toxin content. Land snails consume many types of fungi, even some which are highly toxic to mammals. Their diet usually consists of soil particles as a component. Animal tissue is most likely a very small proportion of the species diet. Commonly, snails start to forage for food around sunset. (Ogle, 2007)

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

Predation

Land snails have a large number of natural predators, including many members of land vertebrates and invertebrates. Birds are one notable predator. They are able to retract the soft parts of their body into their shell to protect it from predators. Land snails are also very susceptible to parasites, which can cause high mortality. (Ogle, 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

  • Known Predators

Ecosystem Roles

Eastern flat-whorl snails play important roles in the ecosystem, such as serving as prey to a variety of predators, and cycling calcium. Land snails often contain parasites, and act as intermediate hosts to parasites which will ultimately end up inside a bird or mammal who consumed the infected individual. Specific parasites that infect the Eastern flat-whorl snail have not been documented. (Ogle, 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

Economic Importance for Humans: Positive

There are no known positive effects of Planogyra asteriscus on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Planogyra asteriscus on humans.

Conservation Status

In 2002 the Minnesota DNR proposed that the Eastern flat-whorl snail status should change to special concern. The Eastern flat-whorl snail currently holds special concern status in Minnesota. It is also a species of special concern in Michigan. ("Distribution and ecology of terrestrial gastropods in northwestern Minnesota", 2002; "Minnesota Administrative Rules", 2013)

Due to their inability to migrate long distances, land snails are extremely vulnerable to habitat degradation. Land use activities that could potentially alter cool, moist, preferred micro-habitats should be avoided, as well as activities that may change hydrologic systems on an ecosystem supporting land snail habitat. Prescribed fire has been recorded to reduce the abundance of land snails. It has been recommended that burn intervals should be separated by 15 years. In addition, it is important to preserve organic litter in sites that support land snails habitats when considering methods of removal of woody and invasive plants. ("Rare Species Explorer", 2007; "Eastern Flat-whorl (Planogyra asteriscus)", 2014)

Contributors

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

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

visual

uses sight to communicate

References

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 http://files.dnr.state.mn.us/input/rules/ets/SONAR_all_species.pdf.

Wisconsin Department of Natural Resources. 2014. "Eastern Flat-whorl (Planogyra asteriscus)" (On-line). Accessed March 14, 2014 at http://dnr.wi.gov/topic/EndangeredResources/Animals.asp?mode=detail&SpecCode=IMGAS21010.

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 http://mnfi.anr.msu.edu/abstracts/zoology/Planogyra_asteriscus.pdf.

The Office of the Revisor of Statutes, State of Minnesota. 2013. "Minnesota Administrative Rules" (On-line). Accessed April 22, 2014 at https://www.revisor.mn.gov/rules/?id=6134.0200.

2007. "Rare Species Explorer" (On-line). Michigan Natural Features Inventory. Accessed March 27, 2014 at http://mnfi.anr.msu.edu/explorer/species.cfm?id=12451.

Cordeiro, J. 2013. "Planogyra asteriscus" (On-line). Nature Serve Explorer. Accessed April 25, 2014 at http://explorer.natureserve.org/servlet/NatureServe?sourceTemplate=tabular_report.wmt&loadTemplate=species_RptComprehensive.wmt&selectedReport=RptComprehensive.wmt&summaryView=tabular_report.wmt&elKey=116849&paging=home&save=true&startIndex=1&nextStartIndex=1&reset=false&offPageSelectedElKey=116849&offPageSelectedElType=species&offPageYesNo=true&post_processes=&radiobutton=radiobutton&selectedIndexes=116849.

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 http://www.uwosh.edu/wisconsinbestiary/animals/slugs-snails/resources/TerrestrialGastropodFaunaNekola.pdf.

Ogle, M. 2007. "Planogyra asteriscus" (On-line). Accessed April 19, 2014 at http://bioweb.uwlax.edu/bio210/2011/ogle_meli/contact.htm.

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