Arrow Crab

Arrow Crab (Stenorhynchus seticornis)

Appearance & Behavior

Long thin legs and a pointed body give this crab a spider-like outline. It actively hunts and scavenges; small body size understates the space needed for its legs.

Quick Care Guide

• Care level: moderate; compatibility and food availability require monitoring.
• Adult size: approximately 2–3 inches body length, with a much greater leg span.
• Minimum aquarium: At least approximately 30 gallons with room for the full leg span.
• Diet: predatory omnivore.
• Reef compatibility: with caution; may prey on or disturb livestock.
• Temperature: approximately 72–78°F for suitable tropical stock; confirm source conditions.
• Specific gravity: approximately 1.023–1.025 for suitable marine stock; match confirmed species requirements and maintain stability.
• pH: 8.1–8.4.
• Alkalinity: 8–12 dKH; prioritize stability.
• Habitat needs: stable rockwork, sheltered molting sites, and protected equipment.

Aquarium Setup & Compatibility

Provide a fully cycled marine system with stable salinity, effective filtration, good oxygenation, and guarded intakes. Provide crevices appropriate to the adult and secure rocks so digging or climbing cannot destabilize them. Use secure containment and avoid narrow equipment gaps.

Keep a realistic separation plan for territorial behavior or predation. Avoid triggers, puffers, predatory wrasses, and other crab-eating animals. Keep stocking conservative and do not assume unfamiliar individuals form a compatible pair.

Reef & Invertebrate Compatibility

May consume worms, small crustaceans, and other vulnerable animals; small fish can also be at risk. Bristleworm predation does not make it safe for all beneficial organisms or guarantee pest control.

Feeding

Offer varied appropriately sized marine shrimp, clam, mussel, and suitable sinking marine carnivore or omnivore preparations. These crabs are not dependable algae-only clean-up animals. Avoid freshwater feeder fish and a single-food diet.

Offer controlled amounts at a frequency suited to the species and condition, and confirm actual intake rather than assuming scavenging supplies enough food. Deliver food near shelter when needed and remove leftovers promptly. Do not overstock a clean-up crew according to a fixed number per gallon or add excess food simply to support unnecessary animals.

Introduction & Long-Term Care

Acclimate carefully to temperature and salinity using a method suited to transport conditions. Transfer in a suitable container where practical, avoiding damage to legs and appendages. Do not pull an animal from its shell or refuge, and keep fingers clear of claws.

Allow undisturbed molting shelter and do not remove an old exoskeleton from the animal by force. An empty molt can resemble a dead crab; check before assuming a loss. Monitor feeding, movement, injuries, and the ability to reach food and refuge. Seek experienced aquatic-veterinary guidance for persistent weakness, food refusal, or repeated molting problems.

Maintain appropriate mineral balance through testing and balanced marine care. Do not dose iodine or other additives blindly. Avoid copper-based treatments and verify medication suitability for the animal before use. Stable water quality and appropriate long-term nutrition matter more than a clean-up crew label.