Green brittle star

Geographical Origin and Habitat: The Green Brittle Star is widely distributed across the tropical waters of the Indo-Pacific region, from East Africa and Madagascar to northern Australia, the Philippines, Indonesia, and East to Fiji. It inhabits coral reefs, shallow lagoons, and rocky crevices at depths of 1 to 30 meters, hiding during daylight.

Taxonomy: Belonging to the class Ophiuroidea, order Ophiurida, family Ophiomyxidae, and genus Ophiarachna. Scientifically described as Ophiarachna incrassata. It is one of the largest brittle star species kept in aquariums, with a central disc diameter up to 5 cm and legs reaching 25 cm.

Social Behavior: Solitary, nocturnal, and predatory. While often sold as a simple cleanup crew member, it is an active hunter. At night, it will form a dome-like cage with its arms over sleeping or slow-moving fish, trapping and consuming them under its central mouth disc.

Coloration and Sexual Dimorphism: The central disc and long, spiny arms are bright olive green to dark green, patterned with light yellow or white dots outlined in black. The arm spines are pale or light-colored. There is no visible sexual dimorphism, and sexes are indistinguishable without microscopic analysis.

Tank Setup: A minimum aquarium volume of 150-200 liters (approx. 40-50 gallons) is recommended. Provide a large amount of mature live rock, structured to create dark caves and crevices where the brittle star can securely hide its central body during the day.

Diet and Feeding: Voracious carnivore. To prevent it from hunting tankmates, feed it directly and regularly. Offer pieces of fresh shrimp, fish fillet, clam meat, mysis shrimp, and large sinking carnivore tablets. Feed near its hiding spot using feeding tongs.

Water Quality: Extremely sensitive to sudden changes in salinity, pH, or temperature, which can cause autotomy (shedding of limbs). Maintain stable parameters: temperature 23-26°C (73-79°F), pH 8.1-8.4, specific gravity 1.023-1.025, and zero copper. Keep nitrates low.

Compatibility and Tankmates: Keep with caution. It is reef-safe for corals but unsafe for small, slow, or ground-dwelling fish (such as small gobies, dragonets, and firefish). Best housed with large, active fish like tangs, angelfish, or triggerfish.

Aquarium Breeding: Spawning in captivity is exceptionally rare. They release gametes into the water column where fertilization occurs. The resulting planktonic ophioplutei larvae are extremely delicate and generally do not survive mechanical filtration systems.

Risks and Diseases: Highly prone to osmotic shock during acclimation; a slow drip acclimation of at least 2 hours is mandatory. Poor water quality or stress will cause tissue necrosis and arm disintegration, which can be fatal if the central disc is affected.