General Information
Freshwater snails come under the phylum mollusca and the class gastropoda. They can be found in almost any freshwater habitat, including ponds, streams, lakes, and rivers (Hamrsky). Many freshwater snails are amphibious, so they can also be found in moist soil, or among plants found near bodies of water. North America has approximately 500 species of freshwater snails (Burch). Within Missouri, there are at least 50 species that come under 8 different families, and each family has multiple genera that come under it (Wu et al. iii). This webpage gives examples of one species within each genus of the 8 different families.
History of Freshwater Snails
According to the Missouri Department of Conservation, freshwater snails originated in saltwater habitats approximately 550 million years ago. Eventually, some of these snails adapted to freshwater habitats, and finally, to land. Aquatic snails with lungs (also known as pulmonates) are the ones that adapted to life on land. Interestingly, it is also hypothesized that some of the freshwater pulmonate snails seen today are descendents of land snails that readapted to living in freshwater habitats.
Basic Anatomy of Freshwater Snails
Freshwater snails are characterised as having a soft body, which is protected by a hard outer shell which is composed of calcium carbonate and other proteins. For most species, the shell is symmetrical, and twisted into a spiral, however, the specific characteristics of these shells, such as shape and color differ from species to species (Burch). The reason why this shell is spiral is because most snails have coiled bodies, so the shell is coiled in order to accomodate the body. It is also important to note that while externally snails might display bilateral symmetry, their internal organs are typically positioned in an asymmetrical manner (Burch). Majority of the snail’s body, known as the visceral mass, is hidden within the shell. However, some parts of the body, known as the head and the foot can be seen outside of the shell when the snail is active. Most snails have the ability to withdraw their head and foot back into their shell if they are threatened by predators, or during unfavourable climatic conditions (Burch).
Snails have several orifices in the head and foot parts of their body. This includes the mouth, anus, mantle cavity (that houses the snail’s gills or lungs), nephridiopore (used to disperse gametes) and male and female reproductive openings (Burch). The mouth is located towards the front of the snail’s body, at the head. Due to torsion of the snail’s body, the anus is also positioned towards the front. Other than the mouth, the side at which these orifices are located depends on the coiling of the snail. In dextral snails, the openings are on the right, whereas in sinistral snails, the openings are on the left (Burch).
There are two main types of aquatic snails: those with gills, and those with lungs. Both of these types of aquatic snails have several species in Missouri (Wu et al. iii). Gilled snails breathe underwater like a clam. A long tube-like structure draws water into the mantle, which is the tissue that connects the body to the shell. Here, the gills extract oxygen from the water, allowing the snail to breathe (Missouri Department of Conservation). These gilled snails also have a structure known as an operculum. This structure is attached to the foot, and seals the opening when the snail goes back into the shell (Burch). This structure protects the snail from predators and even prevents it from drying out in case it is out of water for extended periods of time. Lunged snails, on the other hand, breathe through lung-like structures that are present within the mantle (Missouri Department of Conservation). Many of these lunged snails go above water to breathe, however, many also stay constantly underwater. Unlike gilled snails, lunged snails do not have an operculum (Hamrsky).
Reproduction
How snails reproduce is species dependent. Most gilled snails have separate sexes, while lunged snails are hermaphroditic, meaning that each individual can function as both male and female (Missouri Department of conservation). Eggs are generally laid in clutches, and in a large gelatinous mass. The snails develop fully within the egg, and hatch as tiny snails with shells which are slightly coiled (Hamrsky).
Diet and Methods of Feeding
Freshwater snails are usually omnivores. They generally tend to eat algae, macrophytes and other dead plant and animal debris (Hamrsky). The specific diets can differ from species to species. There are two major ways through which snails eat. The first is through a mouthpiece known as a radula, which has many small teeth like structures in it. During this process, snails scrape against rocks, or the ground, and collect any algae, and food attached to it. This process is known as scraping or grazing (Hamrsky). The other way through which snails eat is through ciliary or filter feeding. This occurs when the snail moves its cilia, causing it to draw in water, along with other nutrients and microorganisms. The water is filtered by the cilia, allowing the snail to consume the nutrients and microorganisms. This means that they intake water with nutrients, and microorganisms, and then filter the water out, consuming the nutrients and microorganisms.
Ecosystem Connections
According to the Missouri Department of Conservation, freshwater snails play an intermediate role in food chains. They consume plants and animal debris, and later become food for larger animals such as fish and birds. Several fish have adapted specialized throat teeth for cracking through snail shells.
Many freshwater snails are intermediate hosts for parasitic flatworms known as trematodes (Missouri Department of Conservation). These worms causes a disease known as schistosomiasis (commonly known as snail fever) in warm-blooded animals. According to the World Health Organization, people get infected by these parasites when larval forms of it penetrate the skin when there is contact with infested water. These larval parasites are released into water by freshwater snails.
Important Vocabulary
These definitions are adapted from Carnegie Museum of Natural History.
Aperture: The opening in the snail’s shell through which the head and foot emerge
Carina: A spiral shell ridge at the outside edge of a whorl
Dextral: This means that the shell is whorled to the right, and the aperture appears on the right side
Globose: Slightly flattened sphere shape
Ovate: Egg shaped
Prosocline: Sloping in a forward direction
Sinistral: This means that the shell is whorled to the left, and the aperture appears on the left side
Whorl: Each 360º revolution on a snail’s shell
Family Viviparidae
Campeloma crassula (previously known as Campeloma subsolidum)
Common name: Ponderous campeloma or Highland campeloma (Wu et al. 3).
Distribution: Found in the drainage systems of the Ozark Plateaus (Wu et al. 3).
Identifying features: Has a large shell which can be up to 32.9 mm long and 20.7 mm wide. The shell is grayish-green to olive green colored and has irregular thin streaks which are reddish to reddish-brown. The aperture is ovate approximately half the shell length (Wu et al. 3). An image of the shell can be found here.
Additional information: These snails are abundant in in the sandy bottoms of rivers where they burrow. This is an ideal environment for them, as the current is sufficient to oxygenate the water column. How these snails feed is unclear, however, it has been hypothesised that they can filter feed. There is also a high chance that the snails can eat by grazing the soft sediments of the river bottom as well. Campeloma snails are said to be parthenogenetic, meaning that they can reproduce without the ovum being fertilized. They are also ovoviparous, meaning that the eggs hatch within the mother’s body (Dillon et al., The Freshwater Gastropods of The Ohio).
Lioplax sulculosa
Common name: Furrowed lioplax (Wu et al. 3)
Distribution: The only records of this species are in the Meramec River, which runs near St. Louis. This species appears to prefer larger rivers, and more lowland-type habitats (Wu et al. 3)
Identifying features: The shell is ovate, medium sized, and can be up to 25 mm. It is thin, and moderately tall. The early whorls carinate, whereas the later whorls are rounded (subcarinate). The aperture is ovate and the color of the shell ranges from light to dark olive (Wu et al. 3). An image of the shell can be found here.
Viviparus georgianus
Common name: Banded mysterysnail (Wu et al. 4).
Distribution: Found in the Eleven Point River in Oregon County. Historically also found in the Current River system in Shannon county (Wu et al. 4).
Identifying features: The shell is large, and can be up to 45 mm and is subglobose, which means that it is not perfectly globe-shaped. The shell is thin, but not fragile, and the color can range from yellowish-green or olive to dark brownish-green. Typically, it has up to 4 evenly spaced reddish or brown colored bands (Wu et al. 4).
Additional information: The species was originally found in Georgia (hence the name), however, it is now more commonly found in the north. It is now also found in the Northeast of the United States, as well as in Canada, as an invasive species. This invasion is likely to be human-mediated. Populations of V. viviparus in Europe, which are closely related to V. georgianus, are documented to feed through filter feeding or ciliary feeding. Grazing is also an option for feeding. The exact life cycle pattern of V. georgianus is unclear, with different studies showing different results (Dillon et al., The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania).
“Pleurocera acuta” by Snek01. https://commons.wikimedia.org/wiki/File:Pleurocera_acuta_shell.jpg
Family Hydrobiidae
Amnicola limosa
Common name: Mud amnicola (Wu et al. 8).
Distribution: Found in both the Meramec River, as well as in tributaries of the Missouri River near Kansas City (Wu et al. 10).
Identifying features: The shell is between 4.0 and 5.0 mm high, and is taller than it is wide. It has 4.5 regularly increasing whorls. The aperture is ovate, and about half the height of the shell. The color can vary from white-ish to brown (Wu et al. 8). An image of the shell can be found here.
Additional information: These snails consume food by grazing, and tend to eat diatoms and other periphyton. The are considered to be semelparous, meaning that they only reproduce once before death (Dillon et al., The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania).
Antrobia culveri
Common name: Tumbling Creek Cavesnail (Wu et al. 11)
Distribution: It is a troglodytic (cave-dwelling) species that is only known to be found in a single stream in Tumbling Creek Cave in the White River basin of the Ozarks (Wu et al. 11).
Identifying features: The shell is between 1.9 and 2.3 mm tall, and slightly taller than it is wide. It has a low, conical spire and 3.5 well rounded whorls. The aperture is subcircular. Finally, the shell is sub hyaline, meaning that it is somewhat translucent, giving the snail a pale yellow appearance (Wu et al. 11).
Additional information: This species is considered endangered on both the state, and federal level. It is only found in a small section of a stream in tumbling creek cave, in southwest Missouri (Wu et al. 11). According to NatureServe, pollution in the 1990s caused by agricultural runoff caused this species to go nearly extinct. This is also the only species is monospecific to the genus Antrobia, meaning that it is the only species within the genus (Wu et al. 11).
“Antrobia culveri” by Snek01. https://commons.wikimedia.org/wiki/File:Antrobia_culveri.jpg
Cincinnatia integra
Common name: Midland siltsnail (Wu et al. 14).
Distribution: There is a chance that historically it would have been distributed across the state, however, currently it is predominantly found throughout the drainage systems of the Ozark Plateaus (Wu et al. 14).
Identifying features: The shell is small, between 5.0 to 6.0 mm tall and is relatively thick and solid. It has 5-6 convex whorls, and the aperture is ovate. The shell has a shiny surface and color can range from greenish to yellow-brown or darker (Wu et al. 14). An image of the shell can be found here.
Probythinella emarginata
Common name: delta hydrobe (Wu et al. 17).
Distribution: Found in the Meramec River, and the lower regions of Missouri River tributaries (Wu et al. 17).
Identifying features: The shell is 3.0 to 5.0 mm and the width is about 0.7 times the height. She shape of the shell can vary from globose (spherical) to subcylindrical. It has 4-5 whorls and the color can vary from white, gray or tan. The aperture is subovate, and approximately 40% as high as the shell (Wu et al. 17). An image of the shell can be found here.
Additional information: This species appears to be mostly abundant at depths of greater than 10 feet of water. They eat by grazing, meaning that they graze the surfaces of rocks for food. They are non-specific for any small particles. P. emarginata are dioecious, with the males having a penis that arises from their neck (Dillon et al., The Freshwater Gastropods of The Ohio).
Marstonia scalariformis (previously known as Pyrgulopsis scalariformis)
Common name: Moss pyrg (Wu et al. 21).
Distribution: Found in the Meramec River (Wu et al. 21).
Identifying features: The shell is 3.5 to 4.7 mm tall, and can range from pupa to conical shaped. It has 5.5 to 6.0 whorls, with early whorls being rounded, and later whorls being nearly flat. The aperture is prosocline, and the color of the shell appears light brown (Wu et al. 21). An image of the shell can be found here.
Additional information: According to NatureServe, this species of snail is critically imperiled, and comes under the S1 category. Missouri and Alabama are the only 2 states where live samples were recently collected.
Somatogyrus rosewateri
Common name: Chert pebblesnail or Elk pebblesnail (Wu et al. 22).
Distribution: This species is endemic to the middle section of the Elk River, from around the Ginger Blue area upto near McDonald County (Wu et al. 22).
Identifying features: The shell is about 4.2 mm tall, and subglobose. It has 4.5 whorls and a protoconch (larval shell), which has many fine spirals and ridges. The color of the shell is greenish, however, it is important to note that this species can appear orangeish, or even brownish, which is caused due to the mantle of the snail showing through the sub hyaline (glassy/translucent) shell (Wu et al. 22).
Additional information: This species has separate male and female sexes. Females are also larger than males, and it is hypothesized that there are more females than males. The females lay eggs singly in firm mud or soil (Wu et al. 22).
Family Pomatiopsidae
Pomatiopsis lapidaria
Common name: Slender walker (Wu et al. 23).
Distribution: Found throughout the state, however, there are some localized occurrences due to habitat preferences (Wu et al. 23).
Identifying features: The shell is between 3.5 to 4.7 mm tall, and can vary in shape from pupiform (shaped like a pupa) to narrowly conic. It has 5.5 to 6.0 whorls, with the early whorls being rounded, and the later whorls being nearly flat. The aperture is prosocline. The color of the shell is light brown (Wu et al. 23). An image of the shell can be found here.
Additional information: This species is amphibious, meaning that it is not only found in bodies of water, but also on moist soil, as well as stems, and leaves of sedges, reeds and cattails. In fact, it is more commonly found out of the water than in it (Wu et al. 23). This species is also sexually dimorphic, meaning that there are separate male and female sexes, with the females being larger than the males. This species lays single eggs, rather than eggs in large clutches (Dillon et al., The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania).
Family Pleuroceridae
Leptoxis arkansensis
Common name: Arkansas mudalia (Wu et al. 27).
Distribution: Only found in central-southern Missouri, in the drainage system of the North Fork of the White River. It is the only species in its genus (Leptoxis) that is known to occur west of the Mississippi River (Wu et al. 27).
Identifying features: Shell can vary from moderately small, to about 10 mm. It is conical, and has a depressed spire. It is important to note that some snails may appear ovate or subglobose, due to erosion of the shell. The aperture is subcircular. The color can vary from tan to brown, and can sometimes even be green to black. It can also vary from uniform to variably banded (Wu et al. 27). An image of the shell can be found here.
Additional information: According to NatureServe, this species of snail is critically imperiled, and comes under the S1 category. Missouri and Arkansas are the only 2 states where live samples were recently collected. This species (along with one other in the genus Leptoxis) lays single eggs, rather than eggs in large clutches.
Pleurocera acuta
Common name: Sharp hornsnail (Wu et al. 28).
Distribution: Commonly found in streams of the Ozark Plateaus. They are also found in the Mississippi River, and some of its tributaries in the northeast of the state (Wu et al. 28).
Identifying features: The shell is tall, and fairly narrow, with flat, and slightly convex whorls. The aperture is sub rhomboidal (meaning that it is somewhat shaped like a rhomboid). The color of the shell can range from tan to brown, and it can vary from uniform to banded (Wu et al. 28).
Additional information: This species feeds by grazing, and consumes a mixture of red and green algae, as well as desmids and diatoms. This species also hibernates when temperatures fall below 5ºC (41ºF). They then re-emerge in the spring in order to lay eggs. These eggs then take about 2 weeks to hatch (Dillon and Kohl).
“Pleurocera acuta” by Snek01. https://commons.wikimedia.org/wiki/File:Pleurocera_acuta_shell.jpg
Family Lymnaeidae
Stagnicola elodes
Common name: marsh pondsnail (Wu et al. 40).
Distribution: Found solely in the Upper and Lower Missouri divisions of the Prairie Region
Identifying features: The shell can range from medium to large sized, and can even be larger than 32 mm. It can range from being fragile to solid. The color is usually olive to brown (Wu et al. 40). An image of the shell can be found here.
Additional information: These snails have annual life cycles. They burrow into loose organic matter during cold or dry weather, and emerge during spring rains. It is during this time that they reproduce. Their diet includes larger algae, and tissue of living microphytes (Dillon et al., The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania).
Pseudosuccinea columella
Common name: Mimic lymnaea or American ribbed fluke snail (Wu et al. 40).
Distribution: Found throughout the Lowland, Southeast Division of Ozark, and Mississippi and Lower Missouri Divisions of the Prairie regions (Wu et al. 41).
Identifying features: Shell can range from medium to large sized and can range from 14.5 to 19.0 mm. It is thin, and fragile. The shell is also transparent and the surface is covered with spiral lines. The aperture can range from ovate to round ovate. The shell is sub hyaline and the color can appear white-ish to brown (Wu et al. 41)..
Additional information: It is unsure as to how this snail consumes food, however, it has a “trophic apparatus” that is well suited to consume filamentous algae, and macrophytes. It is known to be an intermediate host for trematodes, which is a parasitic insect that can cause an infection known as fascioliasis in livestock, and sometimes even humans (Dillon et al., The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania).
“Pseudosuccinea columella” by Snek01. https://commons.wikimedia.org/wiki/File:Pseudosuccinea_columella_shell_3.png
Family Physidae
Physa gyrina
Common name: Tadpole physa (Wu et al. 46).
Distribution: Widely distributed throughout Missouri (Wu et al. 46).
Identifying features: The shell is medium sized, and ovate, but elongated. The surface is evenly spaced with raised lines, and the shell can range from smooth to rough and malleated. The aperture is narrowly ovate. The color of the shell can range from white-ish to brown or chestnut colored (Wu et al. 46).
Additional information: Physa gyrina is considered a “dietary and habitat generalist”, and can thrive under many different environmental conditions. This species can consume detritus, diatoms, filamentous algae, fungi, and living animal and vascular plant material. P. gyrina has evolved to have many different adaptations to protect itself against predators. It can detect predators through “chemical cues” in the water. To protect itself, the snail crawls to “structurally complex” habitats that provide protection. Additionally, this species shows phenotypic plasticity based on these predatorial pressures. In areas with fish that crush the snail’s shell, P. gyrina evolved to have thicker shells. In areas dense with crayfish, P. gyrina evolved to have smaller apertures to reduce the ease with which the crayfish can extract the snail from the shell (Dillon et al., The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania).
“Physa gyrina” by Smithsonian Environmental Research Center. https://flickr.com/photos/117184384@N07/40128486342
Family Planorbidae
Gyraulus parvus
Common name: Ash gyro (Wu et al. 65).
Distribution: Widely distributed throughout Missouri (Wu et al. 66)
Identifying features: The shell is thin, small, and only reaches up to 7 mm in diameter. It has 4-5 whorls, which increase rapidly, and the aperture is round, with a simple margin. The surface of the shell is smooth, and semi-transparent with a white to gray color (Wu et al. 66).
“Gyralus parvus” by Smithsonian Environmental Research Center. https://flickr.com/photos/117184384@N07/38386108562
Helisoma trivolvis
Common name: Marsh ramshorn (Wu et al. 69).
Distribution: Widely distributed throughout Missouri (Wu et al. 69).
Identifying features: The shell is medium sized and tall, and is usually light brown in color. It has a large aperture, which is lunate (crescent shaped) or lunate (Wu et al. 69). An image of the shell can be found here.
Additional information: This species can reproduce by both out crossing, and self fertilization. The large and bulbous shell of this species causes there to be a constant air bubble in it, meaning that it is constantly buoyant. Due to this, it is commonly found floating among vegetation. It has a very strong “trophic apparatus”, allowing it to eat macrophyte tissue and even lettuce. It can also non-specifically graze on periphyton. Finally, it has been used as a model organism for many neurobiological experiments (Dillon et al., 2018).
Planorbula armigera
Common name: thicklip rams-horn (Wu et al. 76).
Distribution: Found in Putnam County in the Chariton River area, and in the southeast Lowland Region and counties near the Mississippi River (Wu et al. 76).
Identifying features: The shell is small, only up to 7.4 mm in diameter. It has 5 whorls, and the aperture is sublunar shaped. The color of the shell is usually brown (Wu et al. 76). An image of the shell can be found here.
Additional information: This species is highly adaptable to different chemistries of water. It has the capability of aestivation in case the habitats are too dry. This means that it can close its aperture with a mucous like substance to preserve the moisture, and then become inactive (Dillon et al., The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania).
References
“Antrobia Culveri.” Results Detailed Report, NatureServe, Mar. 2019.
Burch, John Bayard. North American freshwater snails. No. 3. Malacological Publications, 1989.
“Ciliary Feeding.” A Dictionary of Biology, Encyclopedia.com, 4 Dec. 2019.
Dillon, R. T., Jr. and colleagues 2019. The Freshwater Gastropods of North America Volume 1: Atlantic drainages, Georgia through Pennsylvania.
Dillon, R. T., Jr. and colleagues 2019. The Freshwater Gastropods of The Ohio. Internet address: http://www.fwgna.org/FWGO
Dillon, R. T., Jr. and colleagues 2018. The Freshwater Gastropods of North America. Internet address: http://www.fwgna.org
Dillon, R. T., Jr. and M. Kohl 2013. The Freshwater Gastropods of Tennessee. Internet address: http://www.fwgna.org/FWGTN
Hamrsky, Jan. “Freshwater Snails and Limpets.” LIFE IN FRESHWATER.
“Leptoxis arkansensis” Results Detailed Report, NatureServe, Mar. 2019.
“Land Snails and Slugs of the Mid-Atlantic and Northeastern United States.” Mollusks : Carnegie Museum of Natural History.
“Marstonia Scalariformis.” Results Detailed Report, NatureServe, Mar. 2019.
Missouri Department of Conservation. “Gilled Aquatic Snails (Prosobranch Pond Snails).” MDC Discover Nature.
Missouri Department of Conservation. “Lunged Aquatic Snails (Pulmonate Pond Snails).” MDC Discover Nature.
“Schistosomiasis.” World Health Organization, World Health Organization, 2019.
Wu, Shi-Kuei, Ronald D. Oesch, and Mark Edward Gordon. Missouri aquatic snails. Missouri Department of Conservation, 1997.