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Rock Flower Anemone

Phymanthus crucifer

A colorful and hardy marine anemone native to the Caribbean, forming a circular flower-like disc on the sand bed and displaying vibrant, diverse color patterns.

Taxonomy
Class:Anthozoa
Order:Actiniaria
Family:Phymanthidae
Genus:Phymanthus
Species:Phymanthus crucifer

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Water Temperature

22 - 26 °C

pH Value

8.1 - 8.4

Water type

Marine

Invertebrate type

Anemone

Adult size

15 cm

Minimum group

>= 1

KH

8 - 12 dKH

Ecological role

Symbiont

Species description

Geographical Origin and Habitat: Phymanthus crucifer is native to the tropical waters of the Western Atlantic Ocean and the Caribbean Sea, including Florida, the Bahamas, and the Gulf of Mexico. It is typically found in shallow coastal waters, often partially buried in sandy substrates or anchored to rocks beneath seagrass beds.
Taxonomy: Belongs to the class Anthozoa, order Actiniaria, and family Phymanthidae. Commonly known as the 'Rock Flower Anemone' due to its flattened, circular oral disc surrounded by short, beaded tentacles resembling a flower. Mature specimens typically reach an oral disc diameter of 10 to 15 centimeters.
Social Behavior: It is a semi-sessile invertebrate. While it can move slowly on its basal foot to find a preferred spot with optimal light and flow, it generally stays in one place once settled. It is semi-aggressive but possesses a mild sting, rarely causing damage to adjacent corals unless in direct, prolonged contact.
Coloration and Sexual Dimorphism: Displays extreme color variability; the oral disc can feature concentric or radial patterns in brilliant shades of green, red, orange, pink, purple, and yellow. The beaded tentacles often have contrasting bands. There is no visible sexual dimorphism, and reproduction occurs without gender-distinct traits.

Care, breeding and tankmates

Tank Setup: Requires a well-established marine aquarium of at least 80 liters with moderate to high lighting. Provide a sandy substrate of at least 4-5 cm deep next to stable rockwork, allowing the anemone to attach its foot to a solid surface beneath the sand and retract its body when startled.
Diet and Feeding: Although it derives energy from photosynthesis via symbiotic zooxanthellae, it benefits significantly from regular direct feeding. Spot-feed the anemone once or twice a week with small, meaty foods like mysis shrimp, brine shrimp, or chopped krill using a target feeder or tweezers.
Water Quality: Demands stable marine water parameters: temperature 22°C to 27°C, pH between 8.1 and 8.4, specific gravity between 1.023 and 1.025, and carbonate hardness (KH) between 8 and 12 dKH. Keep nitrate and phosphate levels low, and provide moderate, indirect water flow.
Compatibility and Tankmates: Generally considered reef-safe and compatible with most corals. They can be placed close together to form colorful carpets. While clownfish rarely host in them, small symbiotic anemone shrimp (such as Thor amboinensis) frequently live among their tentacles. Avoid anemone-eating fish.
Aquarium Breeding: Can reproduce sexually by releasing gameti into the water column, or asexually through longitudinal fission. Some advanced hobbyists propagate them by clean bisection through the mouth using a sterile scalpel, though this carries a risk of infection and requires excellent water quality.
Risks and Diseases: The primary risk is the anemone drifting into unprotected wavemakers or overflow grates, which can shred it and foul the water. Secure pump intakes with foam covers. A lack of light or nutrients will cause the anemone to shrink, lose coloration, and eventually detach in search of better conditions.

Geographic Origin and Distribution

Phymanthus crucifer is native to the tropical waters of the Western Atlantic Ocean and the Caribbean Sea, including Florida, the Bahamas, and the Gulf of Mexico. It is typically found in shallow coastal waters, often partially buried in sandy substrates or anchored to rocks beneath seagrass beds.

Origin

Tropical oceans and reefsCentral America and CaribbeanNorth America

Invertebrate profile

Diet
Photosynthetic
The diet of Phymanthus crucifer typically consists of organic detritus, microalgae, or specific planktonic particles. In a home aquarium, they constantly forage along the substrate or rockwork looking for nourishment. Supplemental feeding with specialized invertebrate pellets or liquid foods may be necessary. Ensuring a varied and nutritious diet will promote vibrant colors and long-term health. Overfeeding should be avoided to maintain optimal water quality.
Ecological role
Symbiont
In the wild, Phymanthus crucifer plays a crucial role in maintaining the balance of its native ecosystem. They often act as natural cleaners, breaking down waste materials and unconsumed food. Their constant movement helps aerate the sand bed and prevent the buildup of toxic gases. By managing algae growth, they create space for slow-growing corals and sponges to thrive. A balanced aquarium ecosystem relies heavily on their diligent cleaning efforts.
Shock sensitivity
Medium
This invertebrate is highly sensitive to rapid fluctuations in water parameters. Sudden changes in temperature, salinity, or pH can cause severe osmotic shock and death. A slow and careful acclimation process, preferably drip acclimation, is absolutely necessary. Maintain stable aquarium conditions through regular monitoring and automated top-offs. Avoid performing excessively large water changes at once.
Calcium and minerals
Low
Proper calcium levels are absolutely vital for the structural integrity and growth of this species. They continuously extract calcium carbonate from the water to build their shells, skeletons, or protective tubes. Maintaining calcium levels between 400 and 450 ppm ensures they remain healthy. It is also important to balance alkalinity and magnesium alongside calcium supplementation. Regular testing is required in heavily stocked reef aquariums.
Molting
Yes
If applicable to its morphology, this invertebrate undergoes periodic molting to facilitate growth. During the molting process, the organism becomes extremely vulnerable to predation and stress. It is crucial to provide ample hiding spaces, such as caves or crevices, where they can retreat safely. Do not remove the discarded exoskeleton, as they often consume it to quickly replenish essential minerals. Disturbing them during this delicate phase can lead to fatal complications.
Reproduction
Variable
Reproduction in the home aquarium is often challenging and rare for many invertebrate species. Most require highly specific environmental triggers, such as temperature shifts or lunar cycles. The resulting larvae usually have a prolonged planktonic stage, making them difficult to rear. Specialized food sources like phytoplankton are needed to sustain the offspring. Consequently, most specimens available in the hobby are wild-caught or professionally aquacultured.
Compatibility & tankmates
Verify
Compatibility varies largely based on the specific species and tank mates. They are generally peaceful but can fall prey to aggressive or predatory fish. Ensure they are housed with calm tank mates that will not nip or harass them. Research individual species requirements to avoid territorial disputes. Always monitor new additions carefully to ensure harmonious interactions.

Image gallery

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Last updated: 06/30/2026