Clea helena, formerly known as Anentome helena

The freshwater snail Clea helena is a Southeast Asian species closely related to the marine whelks (family Buccinidae). In the trade it is most commonly called the ‘assassin snail’ or ‘snail-eating snail’.

Among scientists it is also known as Anentome helena and as Clea (Anentome) helena. This latter designation reflects the division of the genus Clea into two subgenera, Clea (Clea) and Clea (Anentome) for the Asian species, and Clea (Afrocanidia) for the African species.

Biology and ecology

Most Clea species prefer flowing water, but Clea helena is also found in lakes and ponds, and this may be why this species adapts well to aquarium conditions. Wild snails are naturally found in waters with silty and/or sandy substrates.

The shell of Clea helena is conical but the apex is commonly worn away or broken off. The shell is yellow with a brown spiral band and is strongly ribbed. Maximum shell length is around 20 mm, though 15-18 mm is more typical. The body itself is peppered grey-green.

Clea helena is a tropical species with a wide distribution across Southeast Asia, and has been reported from Indonesia, Thailand, Malaysia. While most whelks live in the sea, like the other members of its genus, Clea helena is apparently confined to freshwater habitats.

Aquarium maintenance

Broadly speaking it appears to be hardy and easily maintained. My specimens are maintained in a 30-litre aquarium with medium hard, slightly basic water. It does have an obvious preference for sandy conditions, and spends much of its time buried in the sand. A substrate made from smooth silica sand provides an inexpensive way to satisfy this requirement.

Like other small snails Clea helena could be damaged by snail-eating or nippy fish. My specimens coexist with gobies, Aspidoras catfish, and various small snails and shrimps.

Diet

In the wild Clea helena has been reported to feed on decaying protein as well as live prey such as worms and snails. In other words these snails are as much carrion feeders as predators.

Under aquarium conditions they certainly will eat large numbers of small snails including Melanoides tuberculata, Physa spp., and juvenile Tylomelania. Substantially larger snails are ignored, and adult Tylomelania as well as Neritina snails coexist with them happily.

Other foods taken include bloodworms, krill, catfish pellets, and algae wafers.

Reproduction

Clea helena spawns readily under aquarium conditions, though the number of offspring that develop successfully is relatively small. The snails are not hermaphrodites so a reasonably large number of specimens will be required to assure the group contains snails of both sexes. Mating appears to be a leisurely affair, with snails sticking to one another for hours at a time. Often this mating behaviour takes place on the surface of the sand, and sometimes other snails get involved so that several individuals will be stuck together in a group.

Clea helena eggs are laid singly, in small semi-transparent sacs deposited on solid surfaces such as stones and plastic objects in the aquarium. Development appears to be rather slow. Once the eggs hatch the juvenile Clea helena disappear into the sand and are not seen again for several months.

Going by the length of time between the first time eggs were seen and by the size of the largest juvenile Clea helena in my tank, it appears to take at least six months for the snails to reach a shell length of 7-8 mm.

The number of juvenile snails is a small fraction of the number of eggs that were laid, suggesting that various factors prevent the majority of eggs and/or juvenile snails from developing. Cannibalism may be an issue, but the adults ignore the larger juveniles crawling about the tank, so is perhaps less important than might be imagined. Competition for food between the juveniles or with other snails in the sand (such as Melanoides spp.) may be more critical.

These snails spend much of the time buried in the sand

Clea helena is a surprisingly gregarious species, spending much of its time in groups, perhaps mating or engaging in pre-mating behaviours

Breeding is possible, with small numbers of juvenile snails appearing above the sand once they are about 5 mm or so in length