When discussing the large snails of the genus Tylomelania, many people say they are “charming.” Probably no other species of mollusks have become so popular in the aquarium hobby in such a short time as these gentle giants from Sulawesi. And the more attention they get from aquarists, the louder the requests for valid information on the habitat and biology of this genus have become. It is time to correct many false assumptions and half-truths about these snails.
On my trips to my dream island of Sulawesi, Indonesia, in addition to many fish and shrimp species I have found the snails of the genus Tylomelania and observed them in their natural habitat. When studying the limited scientific literature, I have noticed that the genus has hardly been studied at all. That certainly opens up a huge field for malacologists (scientists who study mollusks). Aquarists have known about these snails only since the Sulawesi shrimp boom began in 2007/2008. In addition to the many fantastically colored Caridina shrimp species, various Tylome-lania, with their beautifully shaped shells and attractive colored soft parts, have made dramatic entrances into our tanks.
After a slow but steady spread of the information that these shrimps require high temperatures and slightly alkaline pH values with moderately hard water, it was automatically assumed that the snails from the great lakes of Central Sulawesi also needed to be kept very warm. However, as we know today, this is only partly true. The snails of the genus Tylomelania are spread over large parts of Sulawesi. They live in lakes and rivers at higher elevations but also in the large rivers of the low-lying valleys and in the lowlands. So it is fundamentally wrong to treat them all the same.
Unfortunately, the different eco types are externally indistinguishable to the layman. So here is my problem: how can I introduce these snails so that after reading the article you will be able to decide which animals to get and how to accommodate them? I will first explain the biology of these fascinating animals and their basic care in captivity, and then cover the various biotopes.
The genus Tylomelania belongs to the family Pachychilidae, a family whose membersare spread over large regions of the tropics. The “thicklipped” (from the Greek, pachy = thick, chilus = lip) snails were named for the often heavily thickened edges of their shells. Aquarists also know other species from this family, for example, Faunus and the numerous Brotia species. However, these are only conditionally suitable for aquarium keeping, as they are quite specialized in terms of their reproduction.
The original forms of the modern Pachychilidae must have already existed at the time of the ancient supercontinent Gondwana, since the extant species inhabit all its former parts (Central and South America, Africa, Madagascar, and Australia).
Tylomelania, endemic to Sulawesi, have developed a very special reproductive strategy: they are ovoviviparous. One offspring, surrounded by an egg case, is nourished within the uterus of the parent by secretion. When the young animal hatches from the egg, it is fully developed and enters the world with an already hardened shell. Some Tylomelania species bear juveniles of almost 0.8 inch (2 cm) total length. This is a record for snails.
When a young animal is born, another egg is immediately released from the fallopian tube into the uterus. This is only possible because the environment in their tropical habitat hardly changes. There are no seasons that might affect the successful propagation by altering external factors. Therefore, when keeping them in the aquarium, stable conditions are vital.
Generally, these large snails are not difficult to maintain. Some people keep them in a 3-gallon (11-L) nano tank. The smaller-growing species—some are only about 0.4 inch (1 cm) in size, but are rarely imported—may indeed do well in such a setup, but a snail with a shell up to 4 inches (10 cm) long needs an aquarium at least 24 inches (60 cm) long, preferably bigger. In nature, Tylomelania are highly adapted to their habitat and graze on detritus and algae on wood or stones, or they live on sand, which they chew and sift for food. You will notice very quickly where your snails prefer to hang out in the tank.
Fortunately, these mollusks are not picky and accept any kind of conventional dry or flake food. In addition, you can offer them cooked squash, carrots, or lettuce. Not all species eat the same food, so you might have to experiment a bit. The aquarium may be densely planted, because Tylomelania—at least in my experience—do not touch higher plants.
These snails are mostly purchased in order to keep together with Sulawesi shrimps from the large lakes. However, the imported Tylomelania are not always from the lakes themselves, but are often collected in the cooler tributaries. Some importers do a temperature test by adding one animal to warmer water and one to cooler water and checking to see which one comes out sooner. The correct temperature will make the snail poke its head from the shell and begin to graze.
If the snails feed and feel well, sooner or later offspring will appear. The parents do not care for the babies, and soon you will see all sizes of snails climbing peacefully all over the aquarium substrates, rocks, and wood.
The snails of the genus Tylomelania live in the large lakes of central Sulawesi, as well as in the many tributaries and outlets of these lakes. Various species are imported regularly from the Malili lakes, especially Lake Towutiand Lake Matano, and their surrounding rivers. Years ago the first species came mainly from the Malili drainage, but more recently some have arrived from Lake Poso in the northwest.
First and foremost in numbers imported is the orange Tylomelania sp. from Lake Poso (see cover images). Quite a few aquarists maintain and breed them. This medium-sized species, distinguished by its beautiful orange mantle, comes from the lake itself and requires permanently higher water temperatures. However, in the tributaries I also found a nice similar form that must be kept cool and quickly perishes in high water temperatures.
Especially in the large lakes, in the course of evolution many species developed from one or even several archetypes. This process is called radiation or speciation into several niches and is still in full swing, so it is sometimes difficult to differentiate the species from each other. For example, if you dive into Lake Matano, you immediately notice the numerous Tylomelania sitting on wood or stones. The slight differences in the body color and shell shape are only discernible with closer inspection. But in Lake Poso, I was able to clearly distinguish between the various forms that I found in different habitats.
This radiation has always been accompanied by an extreme adaptation to a particular habitat. A rather large species with a shell length of about 4 inches (10 cm) and a yellow and black striped mantle is observed only on vast sandy areas. The shells are colored brown-black underneath and the tops are covered with a sand-colored calcareous deposit. When in danger, these large snails bury themselves half into the sand and are then well camouflaged. They are covered with little snails of the genus Protancylus, endemic on Sulawesi, who “abuse” their larger cousins as substrate. They resemble marine limpets (Patellidae) but belong to the Planor-bidae (ramshorn snails). I rarely found the 0.4 inch (1 cm) livebearing Protancylus cf. pileolus on other Tylomelania species on wood or stones, even in the immediate vicinity.
Other species are found only on the dead wood abundant on steep banks. They seem to feed on detritus and the sparse algae growth.
Still other species I found only on rocks and boulders in the previously mentioned lakes. In some places in Lake Matano, Tylomelania are so common that I could count at least 68 individuals in a marked area of 10 square feet (1 m2). I staked out the area arbitrarily and then collected the snails the next day, so as not to succumb to the temptation to choose a densely occupied area and bias the result.
Such a population density, of course, raises the question of nutrition. The lakes are oligotrophic and therefore provide only a few nutrients to grow algae. However, the populations of shrimps and snails in some places are enormous. Who is benefiting from whom?
Do the snails eat the abundant shrimp excrement? Near the banks where there are dense stands of trees, falling branches and leaves certainly provide enough nutrients.
So it is no wonder that certain species of Tylomelania are frequently found on decomposing leaves. This behavior is also noticeable in the cooler streams at higher elevations. I found these Tylomelania near Lake Poso and the Matano and Towuti Lakes, as well as much further south in the southeastern part of Sulawesi near the city of Kendari.These animals are commercially available as “Thunderbolt Tylomelania.” Due to the high mineral content of the water, their shells are often covered with calcareous deposits. The layers can be carefully removed to reveal a pretty spiral shell underneath. I found these snails regularly in the sinter (siliceous) terraces below waterfalls, for instance the well-known Saluopa Waterfalls northeast of Lake Poso and the Sumbersari Terraces near Kendari. Large numbers of these snails are found in quiet zones with dense leaf litter.
I could write page after page on the habitats of the species of Tylomelania. There are some new stories about these snails, such as the report that the tiny Zebra Sulawesi Goby, Mugilogobius adeia, in Lake Matano uses the empty shells as spawning caves, similar to the shell dwellers of Lake Tanganyika that use the empty shells of Neothauma.
Tylomelania are certainly still full of surprises. The genus has only been partially explored and offers an incredibly exciting field of study, especially in terms of speciation.
The observant reader will have noticed that I have refrained from talking about the scientific names. Well over 30 different species have been described from these habitats (Rintelen & Glaubrecht, 2005), and probably many more are waiting for their scientific description. I want to avoid the possibility of the wrong species names becoming established, and therefore I usually avoid labeling them on the species level, although in a few cases, I decided to attempt species identification.
More important is to understand how extremely variable this fascinating mollusk genus is and how the species differ in their requirements. On my future trips to Sulawesi I am going to keep an eye on these slow fellows who laboriously make their way through the beautiful underwater landscapes of my dream island.