Encyclopaedia

InvertebrateFreshwaterIntermediate

Assassin snail

Anentome helena

The snail hunter: conical shell with dark brown and yellow spiral stripes — an elegant and extremely useful predator. The only invertebrate in the catalog that is a snail. Specialized carnivore: hunts and consumes pest snails (Physa, Planorbarius, Melanoides) without chemicals. Uses its siphon to 'smell' prey and ambushes from the substrate. Not hermaphroditic: needs male-female pair. Slow reproduction (unlike pest snails). Alkaline, hard water for healthy shell. Sand substrate for burrowing.

Taxonomy

Class:Gastropoda

Order:Neogastropoda

Family:Nassariidae

Subfamily:Anentominae

Genus:Anentome

Species:Anentome helena

Formerly known as:Clea helena

Check out Assassin snail on Atlarium

PracticeRecognition quizzesPhotos, names, origins, and puzzles to review Atlas species.Open quizzes

Water Temperature

21 - 27 °C

pH Value

7 - 8

Water type

Freshwater

Invertebrate type

Freshwater snail

Adult size

2.5 cm

Minimum group

>= 3

6 - 20 dGH

5 - 22 dKH

TDS

140 - 520 ppm

Ecological role

Scavenger

Copper sensitivity

High

Species description

Geographical Origin and Habitat: Endemic to a massive geographical range across Southeast Asia, primarily documented in Indonesia, Malaysia, Thailand, and extending into parts of southern China. Clea helena (the Assassin Snail) naturally colonizes diverse, slow-moving freshwater habitats, including sluggish muddy rivers, shallow drainage ditches, flooded rice paddies, and stagnant jungle pools. These environments are fundamentally characterized by deep, soft substrates (mud or fine sand) where they can bury themselves, and a massive abundance of decaying organic matter and prey snail populations.

Taxonomy: Scientifically classified within the Nassariidae family, a group overwhelmingly composed of marine scavenging snails; Clea helena is a fascinating freshwater exception. Taxonomically, it was formerly known as Anentome helena before reclassification. Morphologically, it possesses a thick, heavily armored, cone-shaped spiral shell (reaching 2-3 cm). Its most defining, highly specialized physical adaptation is an elongated, fleshy tube (the siphon) protruding from the shell, used like a snorkel to breathe and smell prey while completely buried in the sand.

Social Behavior: They are slow-moving, intensely methodical, obligate carnivorous predators and scavengers. Unlike peaceful herbivorous snails, they are active hunters. They spend the vast majority of their time completely buried beneath the substrate with only their siphon exposed, waiting in ambush. When they detect the chemical trail of a prey snail or decaying protein, they emerge and relentlessly track it down. While they are solitary hunters, they congregate peacefully in massive numbers around a large food source (like a dead fish).

Coloration and Sexual Dimorphism: Sexual dimorphism is virtually non-existent; males and females are physically identical to the naked eye, though they are strictly gonochoristic (they require both a male and female to reproduce, they are not hermaphroditic). The coloration is highly distinct and striking, perfectly mimicking the warning colors of a bumblebee or a wasp. The heavily ribbed, conical shell showcases an alternating, high-contrast banded pattern of thick, deep chocolate-brown (or jet black) and vibrant, mustard-yellow stripes.

Care, breeding and tankmates

Tank Setup: The aquarium architecture must perfectly accommodate their deep-burrowing ambush behavior. A minimum 20-liter tank is sufficient for a small group. The absolute, non-negotiable requirement is the substrate: it MUST be exclusively fine, soft sand (at least 3-5 cm deep). If kept on large, sharp gravel or bare-bottom tanks, they cannot bury themselves, causing severe psychological stress and preventing them from hunting naturally. They appreciate dense plantings and leaf litter, which cultivate the pest snails they hunt.

Diet and Feeding: They are strict, obligate carnivores; they will absolutely NEVER eat algae, live aquarium plants, or biofilm. In captivity, their primary biological purpose is pest control: they actively hunt, overpower, and consume massive quantities of "pest" snails (Ramshorn, Bladder, and Pond snails) by inserting a specialized radula into the victim's shell. Once the pest snail population is eradicated, they MUST be heavily supplemented with high-protein sinking carnivore pellets, frozen bloodworms, and pieces of raw shrimp to prevent starvation.

Water Quality: Originating from diverse Southeast Asian habitats, they are incredibly robust, hardy, and widely adaptable. They thrive in standard tropical temperatures (22-28°C / 72-82°F). However, regarding water chemistry, they absolutely demand alkaline, hard water (pH 7.0 - 8.0, GH 8-15). They biologically require massive amounts of calcium to maintain their thick, heavy shells. If kept in soft, highly acidic water (below pH 6.5), their shells will rapidly dissolve, pit, and erode, ultimately leading to a slow, fatal physiological collapse.

Compatibility and Tankmates: They are the ultimate biological control weapon against pest snails, but compatibility requires extreme caution. They MUST NEVER be housed with ornamental snails you wish to keep alive (like Nerite, Mystery, or Rabbit Snails); a pack of Assassins will eventually overpower and kill snails ten times their size. They are 100% safe with all live plants and fast-swimming fish. However, they will opportunistically hunt and eat slow-moving, defenseless dwarf shrimp, especially newborn shrimplets or freshly molted adults.

Aquarium Breeding: Breeding is slow, steady, and entirely manageable (they will not overrun a tank like pest snails). They are not hermaphrodites; a mixed-sex group is required. Following a prolonged, hours-long mating embrace, the female painstakingly deposits single, perfectly square, microscopic, translucent egg capsules on hard surfaces (rocks, wood, or aquarium glass). These eggs take an incredibly long time to hatch (4-8 weeks). The microscopic baby snails instantly burrow into the sand and remain completely hidden for months until they reach juvenile size.

Risks and Diseases: The absolute greatest physical risk is physiological collapse and shell dissolution caused by improper water chemistry (keeping them in soft, acidic water lacking calcium). The second major risk is starvation; inexperienced aquarists often buy them to clear a snail infestation, but fail to provide high-protein sinking food once the pest snails are gone, causing the Assassins to slowly starve to death. Medically, they are instantly killed by copper-based medications.

Geographic Origin and Distribution

Endemic to a massive geographical range across Southeast Asia, primarily documented in Indonesia, Malaysia, Thailand, and extending into parts of southern China. Clea helena (the Assassin Snail) naturally colonizes diverse, slow-moving freshwater habitats, including sluggish muddy rivers, shallow drainage ditches, flooded rice paddies, and stagnant jungle pools. These environments are fundamentally characterized by deep, soft substrates (mud or fine sand) where they can bury themselves, and a massive abundance of decaying organic matter and prey snail populations.

Origin

Tropical oceans and reefsNorth AmericaSouth and Southeast AsiaEast Asia

Invertebrate profile

Diet: Carnivore
Ecological role: Scavenger
Shock sensitivity: Medium
Calcium and minerals: High
Molting: Shell growth
Reproduction: Oviparous
Compatibility & tankmates: With caution

Image gallery

Licensed images linked to the species or, when marked, to the closest representative taxon.

Related species

Recommendations grouped by close relatives, companion choices, and similar care.

Variants and close relatives

Same atlas type, nearby scientific identity, genus, or family.

Acorn dog whelk

Nassarius glans

Species description

Care, breeding and tankmates