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InvertebrateMarineIntermediate

Windowed top snail

Tectus fenestratus

Windowed top snail: marine lumaca marina in the family Tegulidae, included for reef role, behavior, or aquarium utility. Geographical Origin and Habitat: The Fenestrate Top Snail (*Tectus...

Taxonomy

Class:Gastropoda

Order:Trochida

Family:Tegulidae

Genus:Tectus

Species:Tectus fenestratus

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Water Temperature

24 - 28 °C

pH Value

8.1 - 8.4

Water type

Marine

Invertebrate type

Marine snail

Adult size

6 cm

Minimum group

>= 1

Ecological role

Scavenger

Copper sensitivity

High

Species description

Geographical Origin and Habitat: The Fenestrate Top Snail (*Tectus fenestratus*) is a highly utilitarian, reef-safe marine gastropod natively endemic to the warm, sunlit coral reefs, rubble zones, and intertidal flats of the Indo-Pacific Ocean. Their natural biotope is defined by expansive, highly structured reef slopes and rocky outcroppings exposed to bright light, which promotes the heavy growth of the microscopic film algae and diatoms that form their absolute primary food source.

Taxonomy: Scientifically classified within the Tegulidae family, they are frequently confused with and sold interchangeably with *Trochus* or *Astrea* snails. Fully mature adults reach a base diameter of 3.0 to 5.0 centimeters (1.2-2.0 inches). They possess a tall, steeply pitched, conical shell.

Crucial Distinction: Like the Trochus snail, the *Tectus* snail possesses a highly muscular foot and is generally capable of flipping itself back over if it falls off the rockwork, giving it a massive survival advantage over *Astrea*.

Social Behavior: They are slow-moving, entirely peaceful, and strictly herbivorous benthic grazers. They spend 100% of their time meticulously scouring the aquarium glass and live rock surfaces. They are non-aggressive, solitary, and ignore all other tank inhabitants. They are relentless workers, often scaling the glass to the very waterline at night to graze, before retreating to the shaded underside of a rock ledge during the peak lighting hours of the day.

Coloration and Sexual Dimorphism: Sexual dimorphism is visually non-existent. Their coloration is subtle and highly functional for camouflage on a rocky reef. The conical shell is deeply textured with spiral ridges and is typically a mottled, pale grayish-white or beige base color. This is overlaid with subtle, faded reddish-brown or olive-green markings. In a mature reef aquarium, their shells invariably become heavily encrusted in pink and purple Coralline algae, rendering them almost invisible against the rockwork.

Care, breeding and tankmates

Tank Setup: The aquarium architecture MUST accommodate their biological need to graze on hard, algae-covered surfaces. A minimum 40-liter (10-gallon) marine aquarium is perfectly sufficient.

CRITICAL REQUIREMENT: The tank MUST be biologically mature with established live rock and glass surfaces coated in film algae or brown diatoms. Do not add them to a completely sterile, newly cycled, white-rock tank, as they will have absolutely nothing to eat and will perish.

Diet and Feeding: They are absolute obligate herbivores and premier biological cleaners for microscopic algae. They excel at consuming the thin, green film algae that obscures aquarium glass and the brown diatom dust that coats new sand and rocks.

CRITICAL WARNING: They do NOT consume long, filamentous hair algae (like a Turbo snail would). If the glass is perfectly clean and the rocks are bare, they WILL slowly starve to death. Supplement with dried Nori or sinking algae wafers.

Water Quality: As heavily calcified marine mollusks, they are devastatingly sensitive to water chemistry fluctuations. They demand stable tropical heat (24-27°C / 75-81°F). Specific gravity (salinity) MUST be maintained precisely between 1.023 and 1.025. They require hard, highly alkaline water (pH 8.1 - 8.4) with pristine Calcium (400-450 ppm) and Magnesium levels to continually grow their dense, conical shells. Rapid changes in salinity during acclimation will cause instantaneous osmotic shock.

Compatibility and Tankmates: Compatibility is universally absolute for peaceful reef tanks. They are 100% reef-safe, entirely ignoring all corals, polyps, and fish. They are an essential component of the "Clean-Up Crew."

CRITICAL WARNING: Their primary predators in the aquarium are large, aggressive Hermit Crabs. Electric Blue or Hairy Hermit Crabs will actively hunt *Tectus* snails, rip them out of their shells, and steal the shell for housing. Keep them only with dwarf, peaceful hermits (*Clibanarius*).

Aquarium Breeding: Breeding the Fenestrate Top Snail in captivity occurs occasionally through broadcast spawning. Males and females will simultaneously release clouds of gametes into the water column, often triggered by a water change or temperature shift. However, successfully rearing the resulting microscopic pelagic larvae is exceedingly rare in a home aquarium, as the larvae are rapidly consumed by the tank's protein skimmer, mechanical filtration, and hungry corals.

Risks and Diseases:

CRITICAL TOXICITY WARNING: Like all marine snails, they are immediately and fatally hypersensitive to COPPER (Cu) and heavy metals. They will die instantly in tanks treated with copper medications. The second major risk is lethal starvation due to overstocking; placing 20 snails in a pristine 10-gallon tank will result in mass death within weeks. Maintain a realistic ratio of 1 snail per 2-3 gallons of water volume.

Geographic Origin and Distribution

The Fenestrate Top Snail (*Tectus fenestratus*) is a highly utilitarian, reef-safe marine gastropod natively endemic to the warm, sunlit coral reefs, rubble zones, and intertidal flats of the Indo-Pacific Ocean. Their natural biotope is defined by expansive, highly structured reef slopes and rocky outcroppings exposed to bright light, which promotes the heavy growth of the microscopic film algae and diatoms that form their absolute primary food source.

Origin

Tropical oceans and reefs

Invertebrate profile

Diet: Carnivore
Ecological role: Scavenger
Shock sensitivity: High
Calcium and minerals: Medium
Molting: Unlike crustaceans, Tectus fenestratus is a gastropod and does not undergo a molting process to grow. Instead, it continuously adds new calcified layers to the aperture of its existing shell as it matures. Therefore, observing continuous, healthy shell growth lines without pitting or cracks is the best indicator of its well-being.
Reproduction: Oviparous
Compatibility & tankmates: Verify

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.

Pyramid top shell

Tectus pyramis

Species description

Care, breeding and tankmates