News / Species Spotlight / Species Spotlight - Green and Yellow Brittle Stars (Ophiarachna sp.) (01/05/17)

Species Spotlight - Green and Yellow Brittle Stars (Ophiarachna sp.)

Species Spotlight - Green and Yellow Brittle Stars (Ophiarachna sp.)
One of the more diabolical of marine creatures have to be the seemingly benign brittle stars of the genus Ophiarachna. These are commonly seen in the aquarium trade and are often sold to unwitting aquarists to help clean tanks of unwanted detritus. But, unlike most other members of the Class Ophiuroidea, this genus is highly predatory and capable of taking down some surprisingly large prey.

While they will absolutely help in scavenging bits of uneaten food from an aquarium, their specialized hunting behavior always has to be taken into account. During the day, when Ophiarachna is hiding within the holes and crevices of a tanks hardscape, these brittle stars are of little concern. But, when the lights go off and they proceed to move about, smaller fish and shrimp move onto the menu. The feeding strategy is particularly aimed at smaller fishes that move about at night (cardinalfishes are probably high on the list). The brittle star raises up on its five legs, holding its central disk just slightly off the ground. As soon as a fish swims underneath the trap is sprung and the legs twist as the body raises up. This creates a prison, with the prey encapsulated now by the interlocking spiral of the legs. The fate of such fish is a gruesome one, as they slowly begin to be digested by the brittle star headfirst.

To keep this species, it is important that any tankmates be sufficiently large, lest they meet such a grisly demise. This means that smaller gobies, blennies, cardinalfishes, angelfishes and the like are poor choices. For those keeping larger predatory species in a fish-only aquarium, Ophiarachna can make for a perfect tankmate, though be sure to avoid groups that might attempt to nibble on this echinoderm, such as triggerfishes and pufferfishes.

Most of the time, there is no great imperative to directly feed these brittle stars in captivity, as they can usually fend for themselves quite well in a well-fed system, but, as it is admittedly quite fun watching the contortions they make while consuming large pieces of chopped fish and shrimp, these can absolutely make for a highly interactive invertebrate. If handled carefully, this prickly animal can even be briefly held without much issue, which small children tend to find endlessly amusing.

Two color forms exist, one being bright green and the other, from the Central Pacific, being more yellow in appearance. Both can reach upwards of a foot across, making these some of the most visually impressive brittle stars around. For a truly offbeat pet, theres nothing quite like Ophiarachna just be sure to keep those small fishes away.