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I found it in Washington state, in a city south of Seattle. I found it next to a bush after it rained on someone's driveway. Here are two pictures of it:
( originally posted in instagram )
If anyone can identify this species, kudos to you.
It resembles Cepaea nemoralis, or commonly called Grove Snail, belonging to the family Helicidae.
Image Source: WikiMedia Commons
According to Wikipedia, these snails were introduced to North America from Europe. These fascinating creatures occur in diverse forms of shell color as well, as shown below.
Image Source: Metodologie di Programmazione
Here I have found a very detailed shell and body markers for Cepaea nemoralis.
Image Source: ResearchGate
Click through all of our Snail images in the gallery.
Slow-moving but always fascinating, the snail is one of the most ecologically diverse animals on the planet.
Belonging to the phylum of Mollusca, it’s found almost everywhere in the world, from high mountains to simple botanical gardens to deep undersea rocks. The shell is the defining feature of the snail. This is the one thing that separates them from the closely related slugs and sea slugs (although many slugs still have internal shell plates within their bodies). Since the shells contain most of the internal organs, snails cannot survive without shells.
What species of snail is this? - Biology
Common Name: Rosy Wolfsnail, Cannibal Snail
Scientific Name: Euglandina rosea
Original Distribution: E. rosea is native to the southeastern United States.
Current Distribution: E. rosea is currently found in Hawaii, Kiribai, French Polynesia, American Samoa, New Caledonia, Vanuatu, Solomon Islands, Palau, Guam, Northern Mariana Islands, Papua New Guinea, Japan, Hong Kong, Taiwan, North Borneo, Madagascar, Seychelles, Mauritius, Reunion, India, Andaman Islands, Sri Lanka, the Bahamas and Bermuda.
Site and Date of Introduction: E. rosea was first introduced to the Hawaiian Islands in 1955 by the Hawaii State Department of Agriculture to control the giant African snail (Achatina fulica Bowdich), an exotic agricultural pest that was deliberately introduced for garden decoration in 1936. Since 1955, E. rosea has been introduced to more than 20 oceanic islands as a biological control agent for A. fulica and other snail pest species. Biological control is often used to decrease populations of detrimental species to levels where their impacts are insignificant.
Mode(s) of Introduction: E. rosea has been deliberately introducted to numerous areas to control A. fulica, even though there is no indiction that E. rosea has reduced the populations of A. fulica anywhere.
Reason(s) Why it has Become Establish ed: Human activities often provide a very efficient dispersal pathway for exotic species. E. rosea introduction to Hawaii was deliberate. A species that is deliberately introduced often has a greater chance of becoming established, integrated and subsequently invasive than those that are inadvertently introduced. Deliberately introduced species are often able to establish because a large number of individuals are often released. In addition, these individuals usually receive a great amount of care and attention to promote their growth and reproduction.
E. rosea has become established because it is an r-selected species with generalist food requirements, wide habitat tolerance and efficient dispersal. In addition, the fact that E. rosea is native to the Southeastern United States and was introduced to areas with a similar environment enhanced its chances of becoming established.
E. rosea is a cross-fertilizing hermaphroditic species that lay approximately 25-40 eggs a year. It has a much higher reproductive rate than Hawaii’s endemic land snails, which reach sexual maturity at about five years and have a low reproductive rate, giving birth to an average of only four or five live young a year.
Although E. rosea seems to have a preference for endemic snails, it is certainly not a food specialist. It will not hesitate to consume other wolfsnails. Upon hatching, young wolfsnails immediately look for prey and smaller siblings are often eaten. The wolfsnail further supplements its diet with the numerous slug species found in Hawaii as well as the other non-indigenous snails that were introduced for control of A. fulica.
E. rosea is a habitat generalist and lives in both disturbed and undisturbed areas. It has expanded its range from disturbed areas infested with A. fulica and spread into the native forests, into higher elevations where Hawaiian endemic tree snails are found. Although considered a terrestrial invertebrate, in its native habitat, it has been seen crawling up trees and has been known to go underwater in search of its prey.
Ecological Role: Land invertebrate. E. rosea is a source of food for numerous species. In Hawaii, it is preyed upon by the Norway rat (Rattus norvegicus), and the black rat (Rattus rattus). E. rosea serves as an important source of calcium for birds and is especially important during the breeding season when birds need a calcium-rich diet for eggshell formation. However, it is unclear whether E. rosea fills this role in Hawaii since the majority of Hawaiian birds are insectivorous.
Benefit(s): Of the fourteen snail species introduced to Hawaii for the biological control of A. fulica, only three have become established: Euglandina rosea, Gonaxis kibweziensis and Gonaxis quadrilateralis. Among these three, only
E. rosea has become invasive and has exerted a major ecological impact on the native Hawaiian snail fauna. The presence of E. rosea has probably played a role in keeping the populations of G. kibweziensis and G. quadrilateralis down. Since all three species occupy the same ecological niche in Hawaii, which lacks an indigenous predatory snail, competition for resources is inevitable. In such a competition, E. rosea (the larger, more adaptable species) would likely emerge victorious by consuming and outcompeting the other two species. However, the availability of these non-indigenous snails has probably also allowed E. rosea to exist in higher numbers than would otherwise be possible.
Threat(s): Currently, the greatest threat to terrestrial snails in Hawaii has been the exotic rosy wolfsnail. The native snail fauna of the Hawaiian Islands is rapidly disappearing. The terrestrial snail fauna consists of 11 families, most of which have suffered considerable extinction. The native land snails affected include: the family Amastridae, endemic to Hawaii, only ten species of the original 300 remain in the genus Carelia, all 21 species endemic to Kauai are believed to be extinct in the genus Achatinella, 80 percent of the 41 species found on Oahu have become extinct 50 percent of the species in the genus Partulina, found on Molokai, Maui, Oahu, Lanai and the Big Island of Hawaii have been devastated.
Since its introduction, the rosy wolfsnail has become an out-of-control invasive that has developed a taste for the island’s native snail species, driving several to extinction and pushing the entire genus Achatinella onto the US endangered species list. Human activities have further introduced E. rosea to other islands, with similar devastating effect on the local snail fauna. In Mauritius, 24 of 106 endemic snails became extinct, and on the island of Moorea in French Polynesia, E. rosea was responsible for the extinction of seven endemic snails in the genus Partulina.
Control Level Diagnosis: Highest Priority. According to the Global Invasive Species Database, E. rosea is considered one of the world's 100 worst invaders. The presence of E. rosea has been strongly linked to the extinction and decline of numerous snail species in every area where it has been introduced.
Control Method: Conservationists are working to prevent the further spread of E. rosea. Exclosures have been built in Hawaii and French Polynesia to prevent E. rosea from attacking native tree snails. These barriers are somewhat successful but require constant monitoring and maintenance. A toxic bait using snails from the genus Pomacea is being tested in Hawaii.
Cook, Anthony. Feeding Behavior of Euglandina. The Malacological Society of London and the Linnean Society of London. January 21, 1999.
Cowie, Robert H., 1998. Patterns of Introduction of Non-indigenous Non-marine Snails and Slugs in the Hawaiian Islands. Biodiversity and Conservation 7, 349-368.
Cox, George W., 1999. Alien Species in North America and Hawaii. Island Press, Washington, DC.
Howarth, Francis G., 1991. Environmental Impacts of Classical Biological Control. Annual Review of Entomology 36, 485-509.
Loope, Lloyd L., The Effect of Introduced Euglandina Snail on Endemic Snails of Moorea, French Polynesia. September 27, 2002. US Geological Survey Publications.
Euglandina rosea (Ferussac 1821) - Rosy Wolfsnail. October 20, 2002.
Global Invasive Species Programme. Case Study 3.1: Euglandina rosea.
Photos of Euglandina rosea courtesy of the Jacksonville Shell Club.
US distribution map of Euglandina rosea, photo of Pomacea bait and Hawaiian Tree Snails courtesy of Florida State University.
Author: Nokmenee Chhun
Last Edited: 19 November 2002
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Spring is the best time to eat snails, when they are their plumpest, sweet and rich in protein. Snails have been slurped in China for centuries and are an inexpensive treat for a holiday celebration. In contrast to French escargot, which is served with butter and garlic, the Chinese eat snails in stir-fry, braised or boiled and eaten right from the shell. Not all snails are a treat, however, and unfortunately some are extremely damaging to crops and natural ecosystems when they are introduced into a non-native environment.
As host of the 15th Convention of Biological Diversity, China will be leading discussions where controlling invasive species is one of the key actions. Intentional introduction of exotic species has been a part of agriculture for centuries. Two recent examples are the North American crayfish taken to China as a profitable aquaculture species and Asian Carp brought to the U.S. to control algae in ponds—both became costly invasive species. The United States and China are the most likely sources of invasive species, and will likely suffer the most from their effects. The seemingly innocent introduction of snails, for example, has had disastrous impacts on agriculture production and income, human health, and ecosystem diversity.
The Not-So-Slow Apple Snail Invasion in China
The apple snail is an invasive species from South America brought to China in the 1980s for aquaculture. These snails are easy and inexpensive to grow, so entrepreneurial import companies marketed these “golden miracle snails” throughout China from Guangdong to as far north as Liaoning. Sadly, no one had done the market research, so Chinese farmers discovered the apple snail texture was too soft for consumers’ taste and just released the snails. As voracious eaters, the snails eat the roots of aquatic plants, like taro, lotus, water chestnut and especially rice plants. Apple snails also eat frog eggs and the eggs of other snails, threatening the native populations and ecosystems.
Photo Credit: Golden apple snail spawn egg, courtesy of nadtytok/Shutterstock.com.
Damage to rice is a serious threat from apple snails causing annual losses in the Philippines of as much as $2 billion. With an infestation of just one snail every square meter, yield is reduced by 20 percent. Only 8 snails per square meter cause a devastating 90 percent yield reduction.
Controlling apple snails is a challenge. The snails mature within 2 to 3 months and lay up to 8,700 eggs per year. While time consuming, farmers can eradicate the threat by gathering the snails and their clusters of bright pink eggs. Farmers also use ducks as a biological control to eat snails. Besides not being tasty, human consumption of apple snails is not advised as they can carry rat lungworm which causes eosinophilic meningitis in humans. A pesticide is available to kill the snails, but it also kills other snails and shellfish.
The Expensive Giant African Snail Invasion in the United States
Snails have also invaded the United States. The giant African snail is one of the largest snails in the world, measuring up to 8 inches long and lives for 9 years. Smuggled into Florida by a young boy as pets in 1966, three giant African snails were released into a garden by his grandmother. The resulting infestation of more than 18,000 snails took 10 years and over $1 million to eradicate, preventing an estimated $11 million in crop losses. The giant snails eat at least 500 different plants and even the stucco on buildings.
Photo Credit: Giant African snail, courtesy of Olena Kurashova/Shutterstock.com.
Unfortunately, by 2011 giant African snails were back in Florida. A pair of snails produces 1,200 eggs per year, so the U.S. Department of Agriculture (USDA) considers them a top pest threat. By 2013, 128,000 snails were found and destroyed. The USDA has used trained Labrador Retrievers to track down hundreds of snails per week. New attractants have been developed from papaya-flavored oil to bait traps to capture the giant African snail.
China’s Policies Lag the U.S.
Chinese and U.S. customs officials are on the front lines looking for invasive species. Every year, Chinese customs intercepts thousands of batches of foreign pests, as do U.S. customs. In fact, just this year in New York, airport customs officials found 22 giant African snails in a Ghanaian man’s luggage.
Within the United States, the USDA Animal and Plant Health Inspection Service and the U.S. Fish and Wildlife Service regulate and ban the import and transportation of animals and plants. Snails are such a serious threat to agriculture that the USDA prohibits the import of live snails for human consumption and requires permits for zoos, labs, and schools to use snails for educational purposes.
By contrast, policy action on invasives has been slower in China. In 2003, China’s Ministry of Agriculture established an Office for the Management of Invasive Alien Species to collect, catalog, conduct experiments, and set up demonstrations. Since 2015 Chinese laws and regulations to protect biodiversity have been adopted, but gaps remain on managing invasive species. As a sign of their serious intent, the 2020 Biosecurity Law calls for, in Article 18, cataloging information on the major invasive species. Encouragingly, in January 2021, China’s Ministry of Agriculture and other key ministries have set the goal to complete the cataloging and shape actions by 2025, and to control the risk of invasive species by 2035, including the apple snail.
Stricter controls of invasive species are needed as China has extensive problems with ecosystem and agricultural damage. Like every other country except the United States, in 1992 China ratified the Convention of Biological Diversity (CBD), which requires passing new laws. For nearly twenty years U.S. Senators have refused to ratify stating U.S. environmental laws are sufficiently strong. China will host the rescheduled CBD 15th Convention of the Parties in October 2021 in Kunming. As host, China assumed the Convention presidency and has the opportunity to show leadership. While China is making progress in protecting terrestrial environments, non-native aquatic species remain a huge biodiversity threat. The estimated damage from China’s 544 invasive species is more than 200 billion RMB each year according to the Center for Management of Invasive Alien Species.
United States and China Share the Invasive Species Problem
The tale of two snails is just a little slimy microcosm of a much bigger and costly problem for ecosystems, food security and economics in the United States and China. Because the two countries are major trading partners with similar climates, species that are either intentionally or unintentionally (a.k.a. hitchhikers) introduced from one to the other can easily become invasive. U.S.-China relations are currently fraught with tension and conflict, but due to the enormous risks both countries face around invasive species, this should be an area where the two countries renew and expand scientific, policy and customs collaboration to control the import of biological invaders, even small ones like snails.
Karen Mancl is a Professor of Food, Agricultural and Biological Engineering at The Ohio State University and is the Director of the OSU Soil, Environment Technology Learning Lab. She holds a PhD in Water Resources from Iowa State University, an MA in East Asian Studies and an MA in Public Policy from Ohio State University.
Schistosomiasis (Bilharziasis) is caused by some species of blood trematodes (flukes) in the genus Schistosoma. The three main species infecting humans are Schistosoma haematobium, S. japonicum, and S. mansoni. Three other species, more localized geographically, are S. mekongi, S. intercalatum, and S. guineensis (previously considered synonymous with S. intercalatum). There have also been a few reports of hybrid schistosomes of cattle origin (S. haematobium, x S. bovis, x S. curassoni, x S. mattheei) infecting humans. Unlike other trematodes, which are hermaphroditic, Schistosoma spp. are dioecous (individuals of separate sexes).
In addition, other species of schistosomes, which parasitize birds and mammals, can cause cercarial dermatitis in humans but this is clinically distinct from schistosomiasis.
Schistosoma eggs are eliminated with feces or urine, depending on species . Under appropriate conditions the eggs hatch and release miracidia , which swim and penetrate specific snail intermediate hosts . The stages in the snail include two generations of sporocysts and the production of cercariae . Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host , and shed their forked tails, becoming schistosomulae . The schistosomulae migrate via venous circulation to lungs, then to the heart, and then develop in the liver, exiting the liver via the portal vein system when mature, . Male and female adult worms copulate and reside in the mesenteric venules, the location of which varies by species (with some exceptions) . For instance, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine , and S. mansoni occurs more often in the inferior mesenteric veins draining the large intestine . However, both species can occupy either location and are capable of moving between sites. S. intercalatum and S. guineensis also inhabit the inferior mesenteric plexus but lower in the bowel than S. mansoni. S. haematobium most often inhabitsin the vesicular and pelvic venous plexus of the bladder , but it can also be found in the rectal venules. The females (size ranges from 7&ndash28 mm, depending on species) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni,S. japonicum, S. mekongi, S. intercalatum/guineensis) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively .
Various animals such as cattle, dogs, cats, rodents, pigs, horses, and goats, serve as reservoirs for S. japonicum, and dogs for S. mekongi. S. mansoni is also frequently recovered from wild primates in endemic areas but is considered primarily a human parasite and not a zoonosis.
Intermediate hosts are snails of the genera Biomphalaria, (S. mansoni), Oncomelania (S. japonicum), Bulinus (S. haematobium, S. intercalatum, S. guineensis). The only known intermediate host for S. mekongi is Neotricula aperta.
Schistosoma mansoni is found primarily across sub-Saharan Africa and some South American countries (Brazil, Venezuela, Suriname) and the Caribbean, with sporadic reports in the Arabian Peninsula.
S. haematobium is found in Africa and pockets of the Middle East.
S. japonicum is found in China, the Philippines, and Sulawesi. Despite its name, it has long been eliminated from Japan.
The other, less common human-infecting species have relatively restricted geographic ranges. S. mekongi occurs focally in parts of Cambodia and Laos. S. intercalatum has only been found in the Democratic Republic of the Congo S. guineensis is found in West Africa. Instances of infections with hybrid/introgressed Schistosoma (S. haematobium x S. bovis, x S. curassoni, x S. mattheei) have occurred in Corsica, France, and some West African countries.
Symptoms of schistosomiasis are not caused by the worms themselves but by the body&rsquos reaction to the eggs. Many infections are asymptomatic. A local cutaneous hypersensitivity reaction following skin penetration by cercariae may occur and appears as small, itchy maculopapular lesions. Acute schistosomiasis (Katayama fever) is a systemic hypersensitivity reaction that may occur weeks after the initial infection, especially by S. mansoni and S. japonicum. Manifestations include systemic symptoms/signs including fever, cough, abdominal pain, diarrhea, hepatosplenomegaly, and eosinophilia.
Occasionally, Schistosoma infections may lead to central nervous system lesions. Cerebral granulomatous disease may be caused by ectopic S. japonicum eggs in the brain, and granulomatous lesions around ectopic eggs in the spinal cord may occur in S. mansoni and S. haematobium infections. Continuing infection may cause granulomatous reactions and fibrosis in the affected organs (e.g., liver and spleen) with associated signs/symptoms.
Pathology associated with S. mansoni and S. japonicum schistosomiasis includes various hepatic complications from inflammation and granulomatous reactions, and occasional embolic egg granulomas in brain or spinal cord. Pathology of S. haematobium schistosomiasis includes hematuria, scarring, calcification, squamous cell carcinoma, and occasional embolic egg granulomas in brain or spinal cord.
Different Types of Snails.
There are about 55000 species of snails that have been able to adapt to live in different environments, which have made them very abundant all over the world. Next, we will learn about the main ones.
Giant African Snail
Its scientific name is Achatina fulica or African giant snail. These snails are herbivorous and large size. Its shell reaches up to 20 centimeters in length and 7-10 centimeters in height. An adult individual weighs about 32 grams. Their body has two short tentacles and other two long where the eyes are located. Narrow conical shape and appearance, the shell may have 7-9 spirals (whorls) visible on its surface. Their color is not always the same, but it depends on their habitat´s environmental condition. In general, it is slightly dark or reddish brown with yellow vertical stripes.
African snails are included in the list of 100 most damaging invasive species of the world, since they easily adapt to life in regions outside their natural distribution area. They inhabit mainly in warm and humid climates. Although it is a native species of East Africa, African snails have been introduced to many parts of the world over the years and today you can find them in African countries like Ghana, Ivory Coast and Morocco as well as in Hawaii, Australia, Islands, many Caribbean countries and in several Islands and regions of Asia, the Indian Ocean and the Pacific such as China, Bangladesh, Japan, Indonesia, Zealand, , Fiji and Vanuatu. To summarize, the giant African snail is located on all continents except for Antarctica.
Let´s watch them
Garden SNAIL ( Helix aspersa)
These snails are famous because of their slowness, and are also called common snails. They are small mollusks, with a shell of 2.5-3.5 centimeters in height and 2.5-4 cm in diameter. They have a spherical shape and a slightly rough surface, with around 4 or 5 spirals. Not all individuals have the shell of the same color. In some of them it is dark brown, but in most it is brown or clear with a golden hue. Moreover, they have several Brown or yellow veins. The shell has a large opening whose edges are white.
This species is native to the Mediterranean region, but is currently in many areas, making it a species of wide distribution and presence in all continents, with the exception of Antarctica. You can find individuals of Helix aspersa in the lowlands of Great Britain, in the Mediterranean, in the West of Europe, in North Africa including Egypt, in the Iberian Peninsula and in the East of Asia minor, including Turkey. It was also introduced in the United States, where it has thrived in a few regions.
Roman Snail, (Helix pomatia)
The roman snail, Burgundy snail or vineyard snail, is a gastropod mollusk and one of the most well-known and widely distributed snail´s species in the world. They are big snails whose shell measures about 3-4.5 centimeters in height and around 3 to 5 centimeters wide. They a brown hue, 3-5 bands or stripes and 4-5 spiral.
They are distributed in many parts of Central, Southeast, West, East, North and South of Europe, in countries such as Germany, Belgium, Finland, France, Ukraine, Norway, Poland, Italy, Hungary, Austria, Estonia, Albania, Britain, Switzerland, Netherlands and Russia. Given the large number of areas in which they are located, the Roman snails are adapted to life in various types of habitats. In general, they prefer open temperate forests and hedges, vineyards and scrubland areas.
Types of land snails
Land snails are characterized by a soft body, more visible than their marine counterparts. Most land snail species breathe through lungs, although there are some that breathe through a gill system. Therefore, although they are considered terrestrial snails, these snails do require humid environments in order to survive.
Land snails release a type of mucus from the body, which helps to lubricate their muscular foot. This mucus allows them to move through any surface, smooth or rough. Additionally, land snails have a small tentacles on their heads, as well as a primitive brain.
Did you know that the garden snail is considered the slowest of all land snail types? For more, we recommend reading our article where we list the 10 slowest animals in the world.
Keep reading to discover the most common types of land snails:
Invasive snails on the run leave behind DNA evidence
Mark Abramson, of Heal the Bay, displays a New Zealand mud snail on the tip of his little finger at in Medea Creek at Natural Park in Oak Park on Friday March 3 2010. Photo by Brian Vander Brug/Los Angeles Times via Getty Images
DNA sleuthing helped scientists spot early outcrops of a spreading snail invasion in Pennsylvania. The method could be used to spot the unwanted critters before they cause serious damage. That way, conservationists can stop them from conquering even more places.
New Zealand mud snails became a global pest in part because they can reproduce asexually — just one snail in a new area can essentially clone itself until there are 500,000 snails in a single square yard. They’re about the length of a pencil eraser so they’re hard to find until there are so many in a location that it’s nearly impossible to stop their spread.
“It’s kind of weird because as an invasive ecologist, I never really want to find this thing,” says Edward Levri, a Pennsylvania State University-Altoona professor and senior author of a new study published this week in the journal Biological Invasions. “It’s sort of an exciting feeling, it opens the door for us to be able to use this technology to detect the snail at a much wider scale.”
Levri and his colleagues successfully used DNA present in the environment (something researchers call environmental DNA or eDNA) to track down the tiny snails. But over the past decade, Levri has spent a lot of time looking for the tiny rascals by turning over rocks and casting nets. “It is an arduous process, and there’s very limited success,” he tells The Verge.
So this time, he worked with the lead study author James Woodell to collect water samples from eight different locations across Pennsylvania and scour them for the snails’ DNA. Just like humans slough off skin cells in the shower, snails shed DNA in the water. The researchers used a technique called a polymerase chain reaction, or PCR, to amplify small amounts of snail DNA found in water samples. They use a dye to make the DNA glow so that it can be spotted with a special machine.
Biologists led by the University of Iowa used a special technique called eDNA to discover an invasive species of tiny snails in streams in central Pennsylvania where the snails’ presence had been unknown. The invasive New Zealand mud snail has spread to the Eastern Seaboard after arriving in the western United States decades ago. Image: Edward Levri
They ultimately found eDNA from the mud snails in five of the eight locations they sampled. Levri has since been able to go back and find an actual New Zealand mud snail at one of those locations. He hasn’t yet found the snails at the other locations — he hasn’t been able to be out in the field as much as he’d like because of the pandemic. While there’s a possibility that some of the eDNA drifted there from other locations, Levri and co-authors hope the state will consider the eDNA findings as enough evidence to take action.
“From the conservation perspective, that’s enough to say, ‘Hey, we should really be more careful with these sites,” says Maurine Neiman, an associate professor of biology at the University of Iowa and another one of the authors of the study.
The snails are small enough to hitch a ride on fishing gear unnoticed, which is one way they’ve been able to spread across the US and other parts of the world (they can also tag along on boats). The state could put signs up to warn people who fish at these locations to take extra precautions, like cleaning their waders with certain disinfectants before they visit a new fishing location (sticking them in the freezer overnight accomplishes the same thing).
The New Zealand mud snail was first found in Pennsylvania in 2013 at Spring Creek, and now there are “millions” there, according to Levri. That’s bad news for the area’s fish and the people who like to catch them. The snails are difficult to digest and have been known to come out the other end of a fish alive after being eaten. Since they’re a poor source of nutrition, studies have shown that fish that eat them lose weight. The snails also crowd out native snails and aquatic insects. In some cases, the invasive snails make up 90 percent of the invertebrate biomass in a location. That’s “amazing for just one species to do,” says Levri.
“These snails are tiny, but they seem to have the potential to pack a really big ecological punch to these invaded ecosystems,” Neiman says.
eDNA could help researchers find the snails a year or more sooner than they otherwise might have. That gives conservationists crucial time to stop the snails before people unwittingly give them a ride to other, snail-free locales. Conservationists haven’t been very successful in getting rid of the snails once they’ve shown up, Levri says, so that’s all the more reason to stop their spread in the first place.
Biology and Ecology
The phylum Mollusca is one of several invertebrate (animals without a spine) groups and comprises a wide array of animals including gastropods (snails and slugs), cephalopods (squids, octopuses) and bivalves (clams, oysters). Of this group, the primary focus of this tool will be the terrestrial gastropods. In general, snails are often described as those species that possess a shell into which they can retract partially or wholly. Slugs may or may not have shells and for those species that do have shells, it is much reduced and may be internal. Also, for those slug species that have external shells, the shell cannot host the body of the animal and no obvious coiling can be observed.
All terrestrial gastropods have sensory organs referred to as tentacles. There are often two pairs: the larger, upper pair (ocular tentacles) bears the eyes at their tips, and the lower pair (oral tentacles) is used as a sensory organ for detecting odors (Figure 1). Some snail species have only one pair of tentacles (i.e., they lack the ocular tentacles). In these species, the eyes are located at the base of the sensory tentacles. Figure 1
The mouth of the animal is located below the tentacles. It contains a specialized structure known as a radula, which is comprised of a mass of chitinous teeth arranged in rows. The radula is used to scrape pieces of food into the mouth of the animal using a back and forth motion.
The reproductive opening (genital pore) of terrestrial gastropods is generally located anterior-laterally. In snails, the genital pore is located on the head of the animal, just behind the tentacles. Slugs, however, have their genital pore located between the breathing pore and the head, and in some cases this structure may conceal by the mantle. Slugs in the family Veronicellidae are a notable exception to this rule. The genital opening of this group is located ventrally and there are two openings: one that allows access to the female portion of the genitalia and another that allows for the eversion of the male portion of the genitalia.
In most terrestrial gastropods, both sex organs occur in the same organism however, there are a few cases where aphallic (does not have a penis) specimens of normally hermaphroditic species (e.g., Deroceras laeve) do exist. However, there are a few species in which separate sexes occur (e.g., Marisa cornuarietis).
The mantle is a structure that is located on the dorsal surface of the animal, just behind the head, and it mainly functions to secrete compounds that are used to construction the shell. In snails, the mantle is not readily noticeable as it is often restricted to the shell. On the other hand, the mantle of slugs is readily visible and generally extends over the back of the animal, covering anywhere from 30-100% of the dorsal surface (Figure 2). The mantle may extend over the shell of a few species of semi-slugs (e.g., Helicarionidae) when they are active, and can be retracted voluntarily by the animal.
The pneumostome or breathing pore is an opening in the mantle of the animal that supports gas exchange, by serving as the entrance to the animal’s lung. The pneumostome is located on the right side of the animal (i.e., when the animal is positioned with the tail facing the observer, the pneumostome is on the right of the observer).
The ventral portion of the animal bears a muscular structure termed the foot, which is used in locomotion. The skin of the entire animal secretes mucus that aids in the movement of the animal and also serves to reduce dehydration. Many terrestrial gastropods will produce copious amounts of mucus in an attempt to evade potential predators or when irritated.
Figure 2. A: Mantle covering the dorsal surface of the body: A-30%, B-100%.
Figure 3. General Shell Anatomy
Snails and slugs display selective preference for moist, humid habitats (e.g., gardens, forests, wetlands, greenhouses). There are a few terrestrial species that are adapted to environments atypical of terrestrial gastropods (e.g., the snail Cernuella virgata is adapted to living in sand dunes). Snails may aestivate under unfavorable conditions, by retracting into the shell and producing a mucilaginous structure (epiphragm) in the aperture (mouth) of the shell. The epiphragm will desiccate and become papery, thus sealing the aperture to reduce moisture loss. Prior to aestivation, some species prefer to affix themselves to vertical structures such as the sides of buildings, grass blades, and fence posts.
Terrestrial slugs generally prefer to inhabit dark, humid places such as beneath rocks and logs on the forest floor, in leaf litter, and under tree bark during daylight. They are normally nocturnal, although they may be found wandering about during the day after it rains. Snails and slugs feed primarily on plant material (living or dead), mushrooms, and lichens. On occasion, terrestrial slugs and snails may feed on conspecifics, other species of molluscs and their eggs, and calcareous material (e.g., rocks, headstones).
Snails: Juvenile to Adult
It is sometimes difficult to determine if a snail of a given species is a juvenile based solely on its shell. In many cases observation of the genitalia, through dissection of the specimen, is required. As a general rule, the shell of juveniles tend to have brittle apertural lips, whereas the apertural lips of adult specimens are often thickened, rigid and may be reflected in some species (e.g., Otala spp. and Eobania vermiculata). Also, the base of the juvenile aperture curves downward, whereas in adult specimens the apertural lips generally curve outward, rather than downward (Figure 4). Figure 4. Comparison of juvenile and adult shells of Zachrysia provisoria.
The genitalia (formed by the fusion of both male and female structures) are one of the most diagnostic characters of molluscs. In many groups (e.g., Veronicellids), positive species identification cannot be made without the use of the genitalic characters. A generalized diagram of the genitalia can be found in Figure 5. There also may be genitalic structures present in some species and not others. Some of these structures are illustrated in Figure 6. Figure 5. Diagram of a terrestrial mollusc’s generalized reproductive system. Figure 6. Diagram of a terrestrial mollusc’s reproductive system with additional specialized structures.
Parts of the Reproductive System and their Function
- Ovotestis/Gonad: Site of egg and sperm development in hermaphroditic species (i.e., it functions as an ovary and a testis).
- Hermaphroditic duct/Ovotestis duct: Allows for the passage of the gametes to the fertilization pocket.
- Seminal vesicle: Functions in sperm storage (sometimes allow for further sperm maturation), re-absorption and degeneration.
- Albumen gland: The function of the albumen gland is to produce albumen or perivitelline fluid for the egg.
- Fertilization pouch-spermatheca complex (FPSC)/Fertilization pocket (pouch)/Talon/Carrefour/Spermoviduct: As its name suggests, this is the place where fertilization occurs.
- Prostate gland: Functions to produce seminal fluid.
- Bursa copulatrix/Spermatheca/Gametolytic gland: Functions to receive sperm during copulation. It is also said to have a function in sperm degradation.
- Oviduct: Functions to separate the groups of oocytes coming from the ovary into a line in order to increase the chances of being fertilized.
- Vas deferens: Functions to accumulate sperm prior to copulation.
- Vagina/Upper atrium: Functions to receive sperm during copulation.
- Atrium: Allows entry to the reproductive system.
- Flagellum: Used in sperm transfer.
- Penis: Functions to transfer sperm during copulation.
Terrestrial gastropods have the ability to independently manipulate the movement of the eggs and sperm that originate in the ovotestis.
- Sperm cells are continuously produced by the ovotestis and released into the hermaphroditic duct. The sperm cells may be temporarily stored in the hermaphroditic duct in seminal vesicles. When the sperm cells are needed for fertilization, the sperm cells actively migrate from the hermaphroditic duct to the fertilization pocket. Inside the fertilization pocket is a structure called the sperm duct. The sperm duct forms a groove that can be voluntarily closed by the animal during copulation. This functions to prevent self-fertilization when not desired.
- The sperm then migrates to the prostate gland, which produces fluids that provide nourishment to the passing sperm cells. This fluid is very thick and immobilizes the sperm cells. The immobilized sperm cells are then transported towards the vas deferens by the peristaltic movement of the walls of the prostate gland.
- The sperm cells are then transferred from the vas deferens to the penis via the epiphallus. The penis is then everted and the sperm mass deposited into the recipient’s atrium.
- The sperm cells may be transferred directly into the mating partner’s bursa copulatrix.
- A small percentage of the sperm cells deposited into the bursa copulatrix will migrate into the oviduct.
- The sperm cells now migrate from the oviduct into the fertilization pouch-spermatheca complex.
- Eggs are voluntarily released from the ovotestis into the fertilization pouch-spermatheca complex where it will unite with sperms that have migrated there.
- The fertilized eggs (zygotes) are provided with a nutritious albumen coat that is produced by the albumen gland. The eggs are then transported from the fertilization pouch-spermatheca complex into the oviduct section of the common duct where they may be arranged in a line (resembling a pearl necklace). Several layers of material of rich in calcium are then deposited around each egg prior to being laid by the recipient.
- The recipient animal then deposits the fertilized eggs.
It should be noted that self-fertilization could occur in a similar manner as described above, except no donor is involved.