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Melanoides tuberculatus - Die Turmdeckelschnecke (O. F. MÜLLER 1774)

Description:

The slim conical shell of the Malayan trumpet snail (MTS) Melanoides tuberculatus grows 20 to 27 mm long and 7 to 10 mm wide. The 10 to 15 moderately globose whorls increase evenly in size. Older animals often do not have an apex any more due to mechanical wear or low water hardness. The aperture and the corneous operculum are pointed on the upside.

The shell is sculptured by slightly curved lateral ridges and fine spiralling ridges. The operculum is paucispiral and has a strongly excentric nucleus close to the base.

The light horn-colored to brown shell has brown stripes or dots. When the shell is very dark brown or black no dots are visible. The operculum is blackish-brown. The snail's foot is very short and looks like it was cut off in the front. The head is clearly set off from the foot, the active snail stretches it out in a trunk-like manner. The eyes are located at the bases of the thin tentacles.

The snail is mostly grey, light beige or brown in color with yellowish speckles. All in all the species is highly varible in form due to its way of reproduction. Several subspecies as well as dwarf forms have been described (see the paragraph "Forms, subspecies").

Range:

The natural range of the Malayan trumpet snail comprises wide subtropical and tropical parts of Africa and Asia:

In eastern Africa from Natal/South Africa to Egypt. In northern Africa in Morocco and spread to various oases. In the eastern Mediterranean region. In the Middle East practically in every water body (e.g. oases in East Anatolia, Saudi Arabia, Iraq, Iran). In India, Sri Lanka, the Andaman Islands, the Nicobar Islands, Thailand, Malaysia, southern China up to the north, the Japanese Ryukyu Islands as well as in the rest of South-East Asia. In the Indo-Pacific region in all of Indonesia, the Philippines, New Guinea and parts of East Australia. Moreover in Polynesia, Melanesia and Vanatu on most of the South Seas islands.

Scientists assume that the natural range of the Malayan trumpet snail in the Indo-Pacific region was considerably widened by humans (they were spread along with the proliferation of rice fields). Around 1947 aquarists brought the species to the Caribbean region, where it has been spreading ever since: the Lesser Antilles (Guadeloupe, Martinique, Saint Lucia, Grenada), USA (see Web links: USGS), Mexico (Veracruz), Puerto Rico and Panama. All the populations in Europe are also assumed to originate from spreading by humans (aquarists):

Austria (spa Villach and thermae Bad Voeslau), the Czech Republic (Pistany), Hungary (Budapest), the Netherlands (see Web links: Atlasproject Nederlandse Mollusken), Spain (Peníscola south of Tortosa) and Malta. There are scattered populations in Germany in warm waters like e.g. the thermal springs in the Kaiserstuhl, in Schwandorf and in Brandenburg.

Habitat:

The Malayan trumpet snail can be found naturally in various water bodies: From quick-flowing mountain brooks on Madagascar up to 1,500 m above sea level, on the banks of rivers and streams down to the estuaries. Moreover in feeder canals, rice fields, lakes (e.g. in Lake Kinnereth down to 15 m depth), ponds, thermal springs and even in troughs. Mostly it can be found there on sandy or muddy grounds. There are known populations in Oman that live on algae mats and algae-covered stones in shallow water.

Was brought to Turkey : Habitat 4

Water parameters:

The temperatures tolerated by the Malayan trumpet snail in the long run are between 18 and 25 (32)°C. Outdoor populations are known to live in thermal springs, among others, with a water temperature of up to 30 °C (Europe) and even up to 35 °C (Java/Indonesia). The undermost temperature tolerance limit of the species is not as well determined due to seasonal variations in most outdoor waters. However, Melanoides tuberculatus cannot be found in unwarmed waters further north of East Anatolia. When the water temperatures are less than optimal the animals close their operculum and outlive them inactively in the substrate; after too cold a winter they might not wake up again. The species' temperature tolerance was experimented on by MITCHELL & BRANDT (see Web links).

The species is also very tolerant regarding the salinity: Some populations in Florida have been found to live in the brackish water of the mangrove woods in estuaries with a salitiny of up to 30 ppm. Animals around the Dead Sea in Israel grow to especially large sizes in slightly brackish water with a salt content of 4‰.

On Madagascar, the trumpet snail has only been found in water bodies with a hardness over 1°dH.

Very detailed physical and chemical parameters for Lake Kinnereth (Lake Tiberias) – where Melanoides tuberculatus occurs in large numbers – can be found in the "World Lakes Database" on the Internet (see Web links), including the seasonal development of the water temperatures. Further exemplary water parameters of a natural habitat in south-western Turkey have been posted on Aquarienschnecken-Forum (German board – see Web links).

The Malayan trumpet snail's high tolerance towards various water parameters can also be observed in the aquarium: They do well e.g. with very soft to hard water and pH values of 5 to 8.5.

Reproduction:

The Malayan trumpet snail is, like many other front-gilled snails, dioecious. However, the snails practically exclusively reproduce by parthenogenesis, i.e. the females produce offspring without being fecundated first – the young snails are genetically identical with the mother snail. The parthenogenetical offspring are (as they are clones of the mother snails) exclusively female, too.

Up to now, larger percentages of male snails were found in only a few locations, as e.g. in isolated populations in Israel (up to 30%). Only a small number of male snails can be found in Africa. In these bisexual populations the females were also proven to be able to reproduce parthenogenetically. In the majority of all known populations (Asia including India, tank-kept animals) a sexual reproduction has been accounted for as an exception at the most.

A further characteristic of the species is that the Malayan trumpet snail is truly viviparous, i.e. that the embryos hatching from tiny eggs only 0.06 mm in size inside the mother snail are first transferred into a breeding sac in the snail's "nape". There they are fed by special nurse cells, until the offspring's development is complete and they can be released. The nurse cells are detached from the breeding sac epithel and contain, among others, vitamin C, glycogen, fat and proteins. The offspring are released through a musculous breeding borus located 1 to 2 mm behind the right eye. When being released the young snails already have 4 to 6 whorls and a shell length of 1.5 to 2 (max. 4.3) mm. Larger females release larger offspring than snails that have just reached adulthood.

The females of the nominate form reach adulthood with 10 to 11 mm shell length. Depending on the female's size up to 70 embryos/young snails can develop in the breeding sac at a time and independently from the season in various stages. The oldest young snails' positions in the breeding sac are closer to the breeding porus, until they are born foot or apex first. In nature it could be observed that the embryonic development slows down with cooler temperatures, but also that the mother snails can obviously delay releasing their young in adverse conditions. In Lake Kinnereth/Israel e.g., young snails are only born after the winter from mid-May on. Offspring are normally released after dusk and midnight.

Own observations regarding the reproductive behavior in the aquarium:

In the aquarium the young snails are preferredly born after a water change. When water is changed at a e.g. ten-day interval the reproductive intervals of nearly all those snails synchronizes accordingly. Especially if there was a vast amount of food before most of the snails massively release their offspring on the same day at the same hour. Then the water changes were discontinued for three months, however, most of the snails kept their 10-day-interval. In a tank with daily water changes no such rhythm developed. However, in this tank groups of females formed that released their offspring at the same time.

Depending on the size of the mother snail a vaiable number of offspring was observed to be released during each birth (shell length of 2 cm: one young snail; 2.5 cm: one to two young snails; 3 cm: 2 to 5 young snails).

When the population density is very high or the food scarce the females went to areas with a strong current close to the water surface. When the population was not very dense the mother snails did not leave the ground for giving birth or were just seen on the ground for a short time. In the first case an often younger snail can frequently be observed to accompany the mother snail to the strong-current area that sits at the side of the adult animal giving birth. For releasing the offspring, the mother snail tilts its shell to one side. The birth of the first young snail itself takes about 5 minutes, whereas the next young snails follow in one-minute intervals. After that the mother snail and the young snail return to the substrate. If the younger snail only eats the nurse cells and detritus released during the young snails' birth or fulfills further functions is still unclear to the editor.

Life span:

In Hongkong, this snail's life span is 2 to 2.5 years in nature, in Malaysia up to 3.5 years. Snails from the Caribbean lived for over 5 years under laboratory conditions.

Food:

In nature, Malayan trumpet snails feed on diatoms and other algae, detritus, rotting plant parts and carrion in and on the ground. They do not eat living higher water plants. This modesty makes the Malayan trumpet snail also a useful waste-eater in the aquarium. Dead plant parts, leftover (fish) food, excrements of other tank inhabitants and so on are processed to harmless muck by this snail before these substances can start rotting. Thus it is not necessary to feed the Malayan trumpet snails separately in a community tank. In a snail-only tank it also eats food offered in the form of vegetables, food flakes or tablets of every kind. It prefers vegetables and food tablets with a high ve

Behavior:

The Malayan trumpet snail is predominantly nocturnal and mostly searches for food in the ground. As many other snails with an operculum they pertain to the front-gilled snails (Prosobranchia) and can weather inopportune circumstances (like e.g. when the habitat dries out) with their shell closed and dug into the mud. A small quantity of water enclosed in the shell keeps the gills damp enough in order to enable it to indirectly breathe athmosperical oxygen.

As in nature, the Malayan trumpet snail lives nearly exclusively in the ground in the aquarium, too. Only from time to time they can be seen crawling though the aquarium, searching for food. When socialized with lively fish or crayfish the Malayan trumpet snails can be seen a lot more seldomly than in snails-only tanks. In a snails-only tank the Malayan trumpet snail can be observed more frequently above the ground on the food. Especially young snails can be seen feeding on the bacterial film on the water surface. Adult trumpet snails don't seem to be able to float on the surface. When the snails can be seen above the ground in the aquarium this might either be caused by lack of food or an overpopulated substrate. As many other snail species Malayan trumpet snails crawl to the surface when there is a lack of oxygen or other water parameters went bad because there is a little more dissolved oxygen in the water region shortly below the surface air. If the entire snail population shows such a behavior this is an emergency signal that there is a severe problem urgently to be dealt with. This might e.g. be a large rotting fish cadaver, excessively high temperatures (mostly in summer) or a total filter failure.

Special behavior of the young snails in the aquarium:

After leaving the mother snail the offspring start searching for food independently at once. Those young snails released close to the water surface crawl upwards and float there head down, using their foot like a surf board. Often several of them form a small line eating particles of the bacterial film on the surface. After their first meal, the offspring crawl to their proper habitat, the substrate.

If there is suddenly no more food the young snails also crawl to the water surface and hang there with the help of the surface tension. So maybe this behavior does not only serve for eating the bacterial film but might also be a means of drifting to another location.

Keeping in the aquarium:

The Malayan trumpet snail is in many cases not put into the aquarium deliberately but is mostly introduced to the tank in the root balls of aquatic plants. As it is not picky regarding the substrate, the water parameters and other circumstances pretty soon a larger population establishes – at first unknown to the aquarist.

More and more aquarists put those snails into their tanks intentionally as they are very beneficial, or just to watch their behavior.

The Malayan trumpet snail is not only useful as it disposes of food rests in the tank, but it is also called the "aquarists' earthworm" because it is a burrower:

By digging, these snails mix the substrate and thus prevent stinking (oxygen-free) fouling areas in the ground, which are detrimental to plant growth and the overall water quality in the tank. The organic substances (food etc.) processed by the snails can be entirely mineralized by the aerobic bacteria in the ground, are spread evenly in the substrate by the burrowing snails and are thus at the disposal of rooted aquatic plants as a natural fertilizer. However, the snails' digging activity is not as intensive as to dig out established water plants again. There is no special tank set-up necessary for keeping Malayan trumpet snails. Aquariums from 10 l volume on or, respecitively, 20 cm front length are suitable for maintaining a small population.

In order to make their useful work easier for the Malayan trumpet snails a sandy substrate is of advantage, however, they even find their way in chunky gravel.

As Melanoides tuberculatus usually do not dig further down than about 3 cm in the ground depending on their shell size deeper ground layers are only worked through as an exception. Thus substrate deeper than about 4 cm is not really recommendable. The shells of those snails are quite robust and can block a filter pump or gather in CO2 reactors. In order to stretch the maintenance intervals of the filter, sticking the water intake into a piece of fine filter mat is very helpful. Very small snails can only be prevented from being sucked in by covering the intake with a piece of fine gauze, which might clog by other dirt pretty soon, but can be cleaned better than a filter pump if the water intake is a

Socialization in the aquarium:

Due to their burrowing lifestyle these snails can be socialized with nearly all other aquarium animals. When in the same tank with snail-eating crayfish, crabs (in the Mediterranean region, the Malayan trumpet snail shares a habitat e.g. with the freshwater crab Potamon potamios), puffer fish or clown loaches the snails' numbers will be decimated, however, the population usually (not always!) will still maintain itself.

Active Malayan trumpet snails can hardly ever be watched above ground when socialized with the predators mentioned above or with bothersome fish. When socialized with other snails or dwarf shrimp they can be seen a lot more often.

Parasites:

As all freshwater snails, Melanoides can be infested with cercaria (intermediate stages) of various kinds of flukes.

Melanoides tuberculatus serves, among others, as alternate host for e.g. the Chinese liver fluke Clonorchis sinensis (COBBOLD 1872, LOOSS 1907). In order for this parasite to complete its life cycle, infected snails have to be eaten by a fish, and the fish, in turn, by a mammal as final host. Especially in South-East Asia, many people eat infested raw fish and thus are infected with the fluke. A further parasite that makes the Malayan trumpet snail an indirect threat to humans in East Asia is the lungworm Paragonimus westermani (KERBERT 1878, BRAUN 1899). After the trumpet snail the cercaria of this parasite need crayfish or crabs as further alternate host on their way to the final host, a mammal.

The Malayan trumpet snails kept in the aquarium can be considered free from these parasites, as the parasitic life cycle has been interrupted after several snail generations. No infections caused by newly imported Malayan trumpet snails or fish have been known either, as in our culture group usually no raw fish is eaten.

Forms, subspecies:

Due to the nearly exclusively parthenogenetic reproduction of the genus Melanoides there are lots of clonal strains in their wide range, which can vary considerably due to the non-existent genetic interchange over many generations. This makes a differentiation of the genus into real species or subspecies highly difficult from the taxonomist's point of view. According to GLAUBRECHT (1996) about 28 species can be assumed to exist in Africa, and further 9 species in Asia.

Dwarf forms from brackish water on the Seychelles with a maximum of 8.3 mm shell length or huge forms e.g. from Lake Edwar with over 50 mm or Texas with even 70 to 80 (?) mm length are just a few examples for the variability of the species Melanoides tuberculatus.

It is also a known fact that the shells of forms spread in eastern South-East Asia show nearly no sculpturation and very flat whorls.

Generally, the variability in shape of Melanoides tuberculatus has led to the differentiation of geographic subspecies or even independent species, depending on the author. In order to clear these up, further biomolecular and interdisciplinary research is required on an international level.

The editor is still not very clear about which species a form with only 5 to 6 whorls, present in aquaristics for years, belongs to: The weak sculpturation (nearly no spiralling or other ridges) and the flat whorls, however, hint to an origin in Eastern Asia. This form can often be seen above ground in the aquarium and tolerates inopportune circumstances and brackish water better than the nominate for

Additional information:

According to FALKNER (1991) the very commonly found denomination of Melanoides tuberculata is incorrect according to the international rules for nomenclature (ICZN Art. 30b), as genera ending on the suffix -oides are masculine as a rule. The species name thus has to have a masculine ending accordingly (M. tuberculatus). This view, however, is not shared by the German Malacozoological Society (see Web links: www.mollbase.de ), among others.

As taxonomists still seem to be discussing this issue, the editor stays with the name of M. tuberculatus for the time being, in accordance with the international CLECOM lists, FaunaEuropaea and ITIS.

Literature:

GLAUBRECHT, M. (1996): Evolutionsökologie und Systematik am Beispiel von Süß- und Brackwasserschnecken (Mollusca: Caenogastropoda: Cerithioidea): Ontogenese-Strategien, paläontologische Befunde und historische Zoogeographie. Backhuys Publishers, Leiden, NL. ISBN 90-73348-52-8.

[Morphology, anatomy, reproductive biology, range with map etc., in German]

GLÖER, P. (2002): Süßwassermollusken Nord und Mitteleuropas. Bestimmungsschlüssel, Lebensweise, Verbreitung. In: Die Tierwelt Deutschlands. Conchbooks, Hackenheim. ISBN 3-925919-60-0.

[Information about characteristics, range etc., in German]

GLÖER, P & MEIER-BROOK, C. (2003): Süßwassermollusken. Ein Bestimmungsschlüssel für die Bundesrepublik Deutschland. Deutscher Jugendbund für Naturbeobachtung, Hamburg. ISBN 3-923376-02-2.

[Information about characteristics, range map for Germany, in German]

Weblinks:

Atlasproject Nederlandse Mollusken (ANM): Melanoides tuberculatus (MÜLLER 1774) Slanke knobbelhoren

[range map of the Netherlands, in Dutch]

Fauna Europaea

[European Systematics, information regarding the range]

Gulf States Marine Fisheries Commission: Fact Sheet for Melanoides tuberculata (MÜLLER 1774)

[Species description;  locations and range in the Caribbean]

Medical Helminthology(2002)

[Information about various cercaria, their life cycles, hosts and disease symptoms]

MITCHELL, A.J. & BRANDT, T. (2005): Temperature tolerance of the red-rim melania Melanoides tuberculatus, an exotic aquatic snail established in the United States. American Fisheries Society Transaction. 134:126-131.

[only a short version about temperature tolerance is publicly accessible]

www.mollbase.de

[reasoning why the name M. tuberculatus instead of M. tuberculata is used]

SUPIAN, Z. & IKHWANUDDIN, A.M. (2002): Population Dynamics of Freshwater Molluscs (Gastropod: Melanoides tuberculata) in Crocker Range Park, Sabah. ASEAN Review of Biodiversity and Environmental Conservation (ARBEC).

[Information about population dynamics and the habitat of Melanoides tuberculata in Malaysia]

SysTax - a Database System for Systematics and Taxonomy

[Locations of gathered material in Asia]

USGS - Nonindigenous Aquatic Species (NAS) information resource for the United States Geological Survey

[Range map for the USA, short species description]

WIESE, V: (Red.) (2007): Systematische Übersicht der Land- und Süßwassermollusken Nord- und Mitteleuropas.

[Systematics of European molluscs, in German]

World Lakes Database:

[Water parameters of Lake Kinneretz]

YILDIRIM, M. Z. (1995): Türkiye Prosobranchia (Mollusca: Gastropoda)

 [The populations in Turkey, in Turkish]

My special thanx to schneckli for the great co-operation :)

This page was actualized on August 31, 2008

Author: Schneckli

Translator: Ulrike Bauer

Aperture and shell