Common name: Leach's Spider Crab

General Information

The Leach's Spider Crab (Inachus phalangium) is a fascinating and delicate species of crab found in the northeastern Atlantic Ocean and the Mediterranean Sea. Known for its long, spindly legs and small triangular body, this crab is often admired for its unique appearance and its symbiotic relationship with sea anemones. Its cryptic coloration and ability to camouflage make it a master of disguise in its natural habitat.

This species is not commonly kept in home aquariums due to its specific care requirements and relatively low availability in the trade. However, it is occasionally sought after by advanced hobbyists who appreciate its intriguing behavior and symbiotic tendencies. Its role in the ecosystem as a cleaner and scavenger makes it an interesting addition to specialized setups.

Care

Leach's Spider Crab requires a well-established marine aquarium with plenty of live rock and hiding spots. These crabs are relatively small and delicate, so they are best suited to peaceful community tanks with non-aggressive tank mates. They thrive in environments that mimic their natural habitats, such as rocky reefs or areas with soft substrates where they can forage.

Stable water parameters are crucial for their survival, as they are sensitive to fluctuations in salinity, temperature, and pH. Providing a variety of small hiding places and ensuring a low-stress environment will help them thrive.

Diet and Feeding

In the wild, Leach's Spider Crab is an opportunistic feeder, consuming detritus, small invertebrates, and organic matter. In captivity, they can be fed a diet of finely chopped seafood, sinking pellets, and frozen foods such as mysis shrimp. They may also graze on algae and other biofilm present in the tank.

Feeding should be done sparingly, as overfeeding can lead to water quality issues. Offering food once every 1-2 days is generally sufficient to meet their nutritional needs.

Behavior and Compatibility

Leach's Spider Crab is a peaceful and shy species, often seen clinging to rocks or hiding among anemones. They are not aggressive and can coexist with a variety of reef-safe fish and invertebrates. However, they should not be housed with aggressive species that may harm them.

One of the most captivating aspects of their behavior is their symbiotic relationship with sea anemones. These crabs often carry small anemones on their carapace, which provide protection from predators. In return, the anemones benefit from increased mobility and access to food particles.

Symbiosis

Leach's Spider Crab is well-known for its mutualistic relationship with sea anemones, particularly species like Anemonia viridis. The crab carefully places the anemones on its carapace, using them as a shield against predators. This relationship is a prime example of mutualism, as the anemones gain mobility and access to food scraps while the crab gains protection.

In captivity, replicating this symbiosis can be challenging but rewarding. Providing compatible anemones and observing their interaction can be a fascinating experience for advanced hobbyists.

Health and Common Issues

Leach's Spider Crab is relatively hardy but can be susceptible to poor water quality and stress. Maintaining stable water parameters and avoiding aggressive tank mates are key to their health. They are also prone to molting issues if their diet lacks essential nutrients, so a varied and balanced diet is important.

When selecting a specimen, look for active individuals with intact legs and a healthy carapace. Avoid crabs that appear lethargic or have visible signs of damage or disease.

Habitat

Leach's Spider Crab is native to the northeastern Atlantic Ocean and the Mediterranean Sea, where it inhabits rocky reefs, seagrass beds, and areas with soft substrates. They are often found at depths ranging from shallow waters to about 50 meters (165 feet).

Their natural environment is characterized by moderate water flow and plenty of hiding spots, which can be replicated in captivity with live rock and a carefully designed aquascape.