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Hidden Hermit Crab

Calcinus latens

A superb nano-reef hermit crab that diligently patrols live rock. Highly peaceful, it efficiently controls microalgae and detritus, demanding an ongoing supply of appropriately sized shells.

Taxonomy
Class:Malacostraca
Order:Decapoda
Family:Diogenidae
Genus:Calcinus
Species:Calcinus latens

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Water Temperature

22 - 28 °C

pH Value

8.1 - 8.4

Water type

Marine

Invertebrate type

Hermit crab

Adult size

3 cm

Minimum group

>= 1

KH

8 - 12 dKH

Ecological role

Scavenger

Species description

Geographical Origin and Habitat: Calcinus latens is widely distributed across the tropical Indo-Pacific, from the Red Sea and East African coast to Hawaii, the Tuamotu Islands, and south to the Great Barrier Reef of Australia. It inhabits shallow coral reefs, rocky intertidal flats, and tidal pools, typically at depths of less than 5 meters where currents are moderate.
Taxonomy: Belonging to the family Diogenidae and the genus Calcinus, it is commonly known as the Hidden Hermit Crab or Green-shield Hermit Crab. It is a shell-dwelling crustacean that relies on empty gastropod shells to protect its soft, unarmored abdomen, changing shells continuously as it grows throughout its life cycle.
Social Behavior: An active, diurnal, and gregarious species. It spends its time climbing live rocks and scavenging the substrate. While peaceful towards fish and corals, they show competitive behavior toward other hermit crabs over shell ownership. Fighting can occur if there is a shortage of suitable empty shells.
Coloration and Sexual Dimorphism: The walking legs feature a distinctive color pattern, with a greenish-brown or olive base transitioning to a bright white or pale blue band near the tips, which are orange. The left claw is significantly larger than the right claw. Sexual dimorphism is minimal and determined by examining the genital openings on the underside.

Care, breeding and tankmates

Tank Setup: Highly suitable for nano reefs of 30 liters or larger. The aquarium should feature plenty of live rock for climbing and grazing. The most critical care requirement is providing a variety of empty gastropod shells of different sizes (such as Cerithium or Turbo shells) to allow the crab to molt and move into larger homes.
Diet and Feeding: Omnivorous scavenger and detritivore. It is an excellent cleanup crew member, consuming nuisance green algae, diatoms, detritus, and leftover fish food. It does not require target feeding in established tanks but will accept spirulina pellets, dried seaweed, and small pieces of frozen mysis shrimp.
Water Quality: Requires stable marine conditions: temperature 24-28°C (75-82°F), specific gravity 1.020-1.025, and pH 8.1-8.4. It is highly sensitive to copper-based treatments and high nitrate levels. Maintain adequate calcium and magnesium levels in the water to support the development of a healthy new exoskeleton.
Compatibility and Tankmates: Safe for reef aquariums with corals and peaceful fish. They may occasionally target live aquarium snails (such as Astrea or Turbo snails) if they are searching for a new shell. Providing a plentiful supply of loose, empty shells will prevent this predatory behavior from occurring.
Aquarium Breeding: Breeding in captivity is extremely difficult. Mated pairs will spawn, and the female will carry eggs inside her shell until releasing them as swimming zoea larvae. These planktonic larvae are very delicate, requiring specialized rearing setups and micro-plankton feeding regimes to survive.
Risks and Diseases: The primary risk is predation or death due to lack of replacement shells. Without a shell, the soft abdomen is exposed to predators and physical damage. They are also vulnerable immediately after molting, during which they will remain withdrawn deep inside their shell in a protected nook.

Geographic Origin and Distribution

Calcinus latens is widely distributed across the tropical Indo-Pacific, from the Red Sea and East African coast to Hawaii, the Tuamotu Islands, and south to the Great Barrier Reef of Australia. It inhabits shallow coral reefs, rocky intertidal flats, and tidal pools, typically at depths of less than 5 meters where currents are moderate.

Origin

Tropical oceans and reefsAfrica and MadagascarAustralia, New Guinea, and Oceania

Invertebrate profile

Diet
Omnivore
As a herbivore/scavenger, Calcinus latens plays an active role in consuming various organic matters in its environment. Its diet in captivity should be varied, including specialized pellets, frozen foods, and natural algae or detritus depending on its specific preferences. Regular and balanced feeding is crucial for its health and longevity.
Ecological role
Scavenger
The primary ecological role of Calcinus latens is acting as a cleaner within the aquarium ecosystem. By constantly foraging, it helps manage waste, uneaten food, or pests, contributing significantly to water quality. Its presence introduces a natural balance and mimics complex biological interactions found in the wild.
Shock sensitivity
Medium
Calcinus latens is quite sensitive to sudden shifts in water parameters, particularly salinity, temperature, and pH. It is highly recommended to use a slow drip acclimation method over several hours when introducing it to a new tank. Maintaining stable conditions is vital to prevent stress-induced ailments or mortality.
Calcium and minerals
Medium
To support healthy molting and exoskeleton growth, Calcinus latens requires adequate calcium and trace elements like iodine in the water. Regular water changes with a high-quality salt mix usually provide sufficient levels, but specific supplementation may be necessary in heavily stocked reef tanks. Monitoring calcium and alkalinity ensures proper skeletal development.
Molting
Shell growth
During the molting process, Calcinus latens becomes extremely vulnerable to predators and aggressive tankmates. It will typically retreat to a secure hiding spot until its new exoskeleton hardens. It is important to leave the discarded molt in the tank, as the invertebrate will often consume it to reclaim valuable minerals.
Reproduction
Oviparous
Breeding Calcinus latens in a home aquarium is incredibly challenging due to its complex reproductive cycle. It typically involves a planktonic larval stage that requires highly specialized foods and precise water conditions to survive. In most standard setups, any spawned larvae will quickly become food for fish and corals.
Compatibility & tankmates
Peaceful
When considering tankmates, Calcinus latens is generally compatible with peaceful fish and other similarly sized invertebrates. Since its reef compatibility is rated as 'yes', careful observation is required if kept with delicate corals or smaller ornamental shrimp. Aggressive or large predatory fish should always be avoided to ensure its safety.

Image gallery

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

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Variants and close relatives

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Last updated: 06/30/2026