Boxer Crab

Geographical Origin and Habitat: Lybia plumosa is widely distributed throughout the tropical waters of the Indo-Pacific region. It is commonly found among coral rubble, crevices in live rocks, under stones, and in shallow sandy flats of intertidal and subtidal zones at depths of 1 to 15 meters, preferring areas sheltered from strong wave action.

Taxonomy: Belonging to the family Xanthidae. It is a tiny crab species, with adults rarely exceeding 1.5 cm in carapace width. Its chelipeds (claws) are highly modified with specialized, inward-pointing denticles designed specifically to hold and carry small stinging sea anemones, typically from the genus *Bunodeopsis* or *Triactis*.

Social Behavior: It is a shy, peaceful, and cryptic species that spends most of the day hiding under rocks. When threatened by a predator, it waves its claws, presenting the stinging anemones like boxing gloves to deter the attacker. This is one of the most famous examples of obligate mutualism in the ocean.

Coloration and Sexual Dimorphism: The body features a light brown, cream, or pinkish background color, decorated with a distinct mosaic pattern of thin dark lines. The walking legs are banded. The anemones held in its claws are translucent white or light pink. Gravid females carry a conspicuous orange egg mass beneath their abdomen.

Tank Setup: Due to its tiny size, it is highly suited for nano-reef aquariums of at least 20 liters (5 gallons). The tank should be furnished with plenty of live rock arranged to create micro-crevices and caves where the crab can hide. A substrate of fine or medium coral sand is preferred.

Diet and Feeding: Omnivorous and detritivorous. It uses the tentacles of its anemones to mop up organic detritus, microalgae, and food particles from the sand and rock surfaces. In captivity, it feeds on leftovers, crushed flakes, sinking micro-pellets, and fine frozen foods like cyclops or baby brine shrimp.

Water Quality: Keep marine parameters stable: temperature 22-28 °C, pH 8.1-8.4, and salinity at SG 1.023-1.025. Proper levels of iodine and calcium are vital to support successful molting. It is highly sensitive to copper-based treatments, ammonia spikes, and rapid salinity drops.

Compatibility and Tankmates: 100% reef safe. It will not harm corals. Do not house with large, aggressive, or predatory fish (such as hawkfish, dottybacks, puffers, or large wrasses) that might prey on it or stress it into dropping its anemones. Best kept with small, passive species like gobies.

Aquarium Breeding: Breeding in home aquariums is extremely difficult. Mated females regularly carry orange egg masses under their abdomen until they hatch. The pelagic larvae require specialized rearing conditions and micro-phytoplankton food, and are typically lost to mechanical filtration.

Risks and Diseases: The primary risk is the loss of its symbiotic anemones due to stress or physical harassment. If it loses them, it may split a remaining anemone into two halves (which will clone) or find pest aiptasia anemones as replacements. It is highly vulnerable during its molt, requiring safe hiding spots.