Long Tentacle Anemone

The long tentacle anemone is a species that lives on sandy bottoms and buries its foot deep in the sand. Its wide oral disc has radiating pale lines; its tentacles are sparse, very long and often twisted like a corkscrew. Its column is usually orange, red or purple. The tentacle crown can reach 20–30 cm in the aquarium and over 40 cm in the wild. It was long known as Macrodactyla doreensis and was moved to the genus Radianthus in the 2019 revision.

In the wild it hosts several clownfish species, above all Clark's clownfish; in the aquarium ocellaris and percula sometimes accept it and sometimes show no interest at all. Living in the sand reduces its tendency to climb rocks and wander among the corals; in this respect it is one of the easier anemones to manage in a reef. Specimens in the trade are wild-collected.

It lives on shallow sandy and muddy flats at the edges of reefs from Japan to Indonesia, the Philippines, New Guinea and northern Australia. It attaches its foot to a stone or piece of shell beneath the sand; when threatened it can pull its whole body into the sand.

• Volume: at least 200 liters; a mature, stable reef.
• Sand: fine to medium-grained sand at least 10 cm deep; flat stones beneath the sand where it can attach its foot. Large, sharp coral rubble injures its foot.
• Water: salinity 1.024–1.026 specific gravity, pH 8.1–8.4, temperature 24–27°C; nitrate and phosphate should be low.
• Light and flow: moderate to strong lighting and moderate flow; pump intakes should be covered with sponges.
• Reef compatibility: Reef-safe with caution. Its long tentacles sweep a wide area; corals on the sand or on nearby rocks should be placed with a gap in between.
• Acclimation and medication: Acclimate by the drip method for at least 1 hour; copper-based medications are lethal.

Carnivorous. In addition to the nutrition it gets from light, it should be given mysis, chopped shrimp or mussel 1–2 times a week. The morsel is placed on the tentacles or near the mouth; very large morsels are regurgitated.

If it does not like its spot, it moves by sliding slowly across the sand. At night it partially draws in its tentacles. Its tentacles are sticky and stinging; it can catch small fish swimming past.

Good companions: Clark's, pink skunk and orange-fin clownfish; ocellaris and percula; sexy shrimp, peaceful reef-safe fish.

Avoid: butterflyfish and angelfish that pick at anemones; large sand sifters that constantly churn the sand bed; anemones of other species.

Start the aquarium with a single individual. In large aquariums a second individual can be added only if a wide stretch of sand is left between them.

In the wild the sexes are separate and it releases eggs and sperm into the water; the larvae develop in the plankton and settle on a sandy bottom. No offspring are obtained this way in home aquariums.

• Bleaching: loss of color is the loss of its symbiotic algae; light, temperature and feeding should be checked.
• Leaving the sand: an anemone that keeps pulling its foot out of the sand and wandering is unhappy with the grain size or depth of the sand.
• Death: a dead anemone rots quickly and poisons the water; it must be removed immediately.

Cannot be told apart externally.