Arrow Crab

Arrow Crab: The Bristleworm Hunter

The Arrow Crab (Stenorhynchus seticornis), also known as the Yellowline Arrow Crab or Spider Crab, is a popular and instantly recognizable marine invertebrate. It is easily identified by its long, thin, spider-like legs and its distinctively triangular, arrow-shaped carapace (body) that tapers to a long, pointed rostrum (snout).

Native to the Western Atlantic, including the Caribbean, this crab is often sought after for its appetite for nuisance pests, particularly bristleworms, which it actively hunts and consumes. Its coloration typically consists of a whitish or tan body covered in fine dark lines, with its long legs sometimes banded with red, yellow, or brown, and its claws tipped with striking blue or violet.

The Arrow Crab is a relatively hardy and long-lived addition to a mature saltwater system, but its opportunistic and territorial nature requires careful consideration when selecting tankmates.

Diet & Compatibility:

• Diet: The Arrow Crab is an opportunistic Carnivore / Scavenger. Its natural diet includes small invertebrates, detritus, and worms. Its most desirable function in the aquarium is its effective control of unwanted Bristleworms and small feather duster worms.
• Feeding: While it will scavenge for leftovers and pests, it should be spot-fed meaty foods several times a week to prevent it from preying on desirable tankmates. Offer pieces of frozen shrimp, squid, clam, or sinking invertebrate pellets.
• Reef Compatibility: It is generally considered Reef Safe With Caution. It will not consume most corals, but a hungry or large specimen may pick at soft corals, zoanthids, or mushroom polyps while searching for small prey or detritus. Provide ample food and hiding spaces to mitigate this risk.
• Temperament: It is Semi-Aggressive and highly Territorial, especially towards its own species. Do not house two Arrow Crabs together in tanks under 75 gallons, as they will often fight to the death. It may pose a risk to ornamental shrimp (like Cleaner Shrimp) and small, slow-moving fish, especially at night when it is most active.
• Aquarium Requirements: Provide plenty of live rock with caves, crevices, and ledges for hiding during the day, as this species is primarily nocturnal.

Quick Facts

• Scientific Name: Stenorhynchus seticornis
• Primary Common Name: Arrow Crab
• Other Common Names: Yellowline Arrow Crab, Spider Crab, Decorator Arrow Crab
• Origin: Western Atlantic (Caribbean, North Carolina to Brazil)
• Max Size (Leg Span): 6-10 inches (15-25 cm)
• Temperament: Semi-Aggressive / Territorial (Predatory toward small inverts/fish)
• Diet: Carnivore / Scavenger (Excellent Bristleworm hunter)
• Minimum Tank Size: 30 Gallons (75+ Gallons for multiple crabs)
• Reef Compatibility: With Caution (May pick at corals if underfed; predatory toward small shrimp)
• Care Level: Easy