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InvertebrateBrackishIntermediate

Brackish assiminea snail

Assiminea grayana

The Dunedin Snail is a tiny, amphibious gastropod native to North Sea mudflats. It is strictly for brackish paludariums, as fully submerged freshwater setups are fatal.

Taxonomy

Class:Gastropoda

Order:Littorinimorpha

Family:Assimineidae

Subfamily:Assimineinae

Genus:Assiminea

Species:Assiminea grayana

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Water Temperature

15 - 28 °C

pH Value

7 - 8.5

Water type

Brackish

Invertebrate type

Freshwater snail

Adult size

0.8 cm

Minimum group

>= 1

10 - 30 dGH

3 - 15 dKH

TDS

180 - 600 ppm

Ecological role

Scavenger

Copper sensitivity

High

Species description

Geographical Origin and Habitat: The Dunedin Snail (*Assiminea grayana*) is a microscopic, highly specialized amphibious gastropod natively endemic to the massive coastal estuaries, high salt marshes, and tidal mudflats surrounding the North Sea and the English Channel. Their natural biotope is defined by the high-tide line (supralittoral zone) where the land meets the sea. They are truly amphibious scavengers, spending a vast majority of their lives completely out of the water, traversing damp mud, decaying saltgrass, and wet driftwood.

Taxonomy: Scientifically classified within the Assimineidae family, they are exceptionally tiny, often overlooked micro-snails. Fully mature adults are astonishingly small, rarely exceeding 0.4 to 0.6 centimeters (0.15-0.23 inches) in shell length. They feature a smooth, rounded, somewhat translucent conical shell with slightly convex whorls. Despite their microscopic size, they breathe via gills and possess a functional operculum. Their most defining feature is their highly reduced, stubby sensory tentacles.

Social Behavior: They are peaceful, highly gregarious, and distinctly amphibious scavengers. In the wild, they swarm in massive numbers, clinging to the damp stalks of salt marsh grasses (*Spartina*) just above the waterline to avoid prolonged submersion and marine predators. Their behavior is strictly terrestrial-adjacent: they despise being fully submerged in deep water. Instead, they tirelessly patrol the wet waterline, grazing on microscopic fungal and bacterial films covering decaying organic matter.

Coloration and Sexual Dimorphism: Sexual dimorphism is visually non-existent due to their microscopic size. Their coloration is entirely utilitarian, designed to blend perfectly with estuarine mud and decaying vegetation. The smooth, slightly glossy shell is typically a uniform, semi-translucent pale brown, dark amber, or horn color, entirely lacking the bands or complex patterns found on larger marine snails. Their tiny, fleshy body is generally a pale, translucent yellowish-grey with a visibly dark snout.

Care, breeding and tankmates

Tank Setup: The aquarium architecture MUST accommodate their amphibious, brackish-water biology. A standard, fully filled aquarium is a death trap. A minimum 20-liter (5-gallon) paludarium or tidal setup is required.

CRITICAL REQUIREMENT: They MUST have extensive access to damp land areas, emergent rocks, or exposed mudbanks; they will drown or exhaust themselves if forced to remain fully submerged. A tight-fitting lid is mandatory to maintain 100% atmospheric humidity and prevent escapes.

Diet and Feeding: They are microscopic detritivores and biofilm grazers. They DO NOT consume living aquatic plants. In a proper paludarium, they require zero targeted feeding; they survive entirely by vacuuming the microscopic fungal spores, bacterial slime, and decaying plant matter that naturally accumulate on damp wood and wet mud. If kept in highly sterile setups, their diet must be supplemented with minuscule pinches of powdered spirulina dusted directly onto the emergent land areas.

Water Quality: Originating from the salt marshes of the North Sea, they are highly adaptable to temperature but demand specific salinity. They tolerate cold to warm temperatures (10-25°C / 50-77°F).

CRITICAL SALINITY REQUIREMENT: They are an estuarine species; the water feature of their enclosure MUST be brackish (Specific Gravity 1.005 - 1.015). Placing them in 100% pure freshwater will slowly disrupt their osmotic balance and cause premature death. The water must be hard and alkaline (pH 7.5 - 8.2).

Compatibility and Tankmates: Compatibility is heavily restricted by their microscopic size and requirement for a brackish paludarium environment. They are perfect for specialized mudskipper habitats, brackish vampire crab enclosures, or species-only tidal setups. They MUST NEVER be housed with any fish, crabs, or large snails that could easily crush or accidentally swallow them. Because they spend 90% of their time out of the water, aquatic tankmates are largely irrelevant to their daily lives.

Aquarium Breeding: Breeding *Assiminea grayana* is exceptionally difficult in captivity. While they are dioecious (separate male and female sexes) and lay microscopic egg capsules in the damp mud, the emerging larvae require complex, fluctuating tidal cycles and highly specific brackish water chemistry to survive. Consequently, despite their massive swarms in the wild, they almost NEVER successfully reproduce or establish self-sustaining populations in standard home aquariums.

Risks and Diseases: The absolute greatest physical risk is agonizing death by drowning; owners fail to realize they are an amphibious species and force them into fully filled aquariums without emergent land. The second major risk is lethal desiccation; if the paludarium is not sealed to maintain 100% humidity, their tiny bodies will rapidly dry out and die. Finally, placing this estuarine species in 100% pure, soft freshwater will cause slow, lethal osmotic failure.

Geographic Origin and Distribution

The Dunedin Snail (*Assiminea grayana*) is a microscopic, highly specialized amphibious gastropod natively endemic to the massive coastal estuaries, high salt marshes, and tidal mudflats surrounding the North Sea and the English Channel. Their natural biotope is defined by the high-tide line (supralittoral zone) where the land meets the sea. They are truly amphibious scavengers, spending a vast majority of their lives completely out of the water, traversing damp mud, decaying saltgrass, and wet driftwood.

Origin

Europe, Mediterranean, and West AsiaEast Asia

Invertebrate profile

Diet: Biofilm grazer
Ecological role: Scavenger
Shock sensitivity: High
Calcium and minerals: High
Molting: Shell growth
Reproduction: Oviparous
Compatibility & tankmates: Peaceful

Image gallery

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

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Species description

Care, breeding and tankmates